Important notes(1) Even where a ductwork job specification calls for the systemto be wholly in accordance with DW/142, it will still be necessaryfor the designer, in addition to providing drawings showing detailsand dimensions of the ductwork, to identify his particularrequirements.The Technical Information to be Provided by Designer istherefore set out in detail on the reverse of this flap.

(2) While it shall be mandatory for high-pressure ductwork (asdefined in this specification) to be tested for air leakage inaccordance with the procedure set out in Appendix B, no suchtesting of low- or medium-pressure ductwork is required unless sostated in the job specification (see 6.4).

Part One- Technical Informationto be provided by designer

For each ductwork system, the designer shallprovide the information covered by 1.1 and 1.2,and shall also state any departure from thestandard specification in respect of 1.3, 1.4 and1.5.

1.1 Pressure classification (Table 1)1.2 Leakage classification (Table 2)1.3 Materials (Section 7)1.4 Negative pressures (Table 1)1.5 Variable air volume (Section 9.2)

The designer shall (where relevant andpracticable) provide information in respect oftheitems 2.1 to 2.5.

2.1 Access openings (Section 21)Number and location of all access doors, accesspanels, test holes and instrument openings, .other than those regarded as standard practice.2.2 Control dampers (Section 22)Details and location of all control dampers.2.3 Fire dampers (Section 23)Specification and location of all fire dampers tomeet the requirements ofthe Authority directlyconcerned with fire regulations.2.4 Bendable/flexible ducts (Sections.24 and 25) '.Details and location of any flexible ducts andconnections.2.5 Flexible joints (Section 26)Details and location of any flexible joints.

The designer shall also (where relevant andpracticable) provide information in respect of theitems 3.1 to 3.10.

3.1 Air leakage testingThe extent of any leakage testing required forductwork other than high-pressure (see 6.4);and the method of testing if different from thatset out in Appendix B (page TI).3.2 Protective treatments (Section 28)Details and specification of any fire resistant orother special protective treatment.

3.3 Special finishes (Section 28)Details of any special finishes required, e.g.galvanizing after manufacture, metal spraying,plating, anodizing, special paints.

3.4 Thermal insulation (Section 31)The extent (if any) to which the ductwork is tobe insulated and details of the type of insulationto be applied.

3.5 Vapour sealing (Section 19.6)The extent (if any) to which vapour sealing is tobe applied to insulated ductwork; and if so,whether to be to Method 1 or Method 2.

3.6 Acoustic treatment (Section 30)The extent (if any) to which any acoustic liningor any other treatment is to be provided for theductwork; and by whom, with detailedspecification.

3.7 Attachment to building structure (Sections19 and 29)Details of any limitations on the attachment ofthe ductwork to the building structure(including any special provisions designed toprevent the transmission of vibration; or of anyspanning steelwork or special ductworksupports not covered by this specification.

3.8 Variable air volume systemsIdentification of any part of the ductworksystem requiring modified construction, e.g. tocounteract exceptional changes in pressurewhen the system is in operation which mightotherwise give rise to an 'oil-canning' effect.

3.9 Negative pressuresAny exceptional stiffening required to preventunacceptable panel distortion and excessive airleakage if negative pressures are likely toexceed the limits set out in Table 1 (page 13).

3.10 Other requirementsDetails of any requirements for the ductworknot in accordance with the provisions of thisspecification, including any modifiedconstruction required to conform with anyregulations concerning external ductwork or tomeet the requirements of a local authority orother controlling body.

·~·~DW/142·.:-. ·Specificationfor sheet metal ductwork.~.~ Low, medium and high ... -.pressure/velocity air syStems 1982

COPYRIGHT © 1982by theHeating and VentilatingContractors' Association

All rights reserved

HEATING AND VENTILATINGCONTRACTORS' ASSOCIATION

Esca House, 34 Palace Court,London W2 4JGTelephone: 01-229 2488

Telex: 27929

Obtainable from: HVCA Publications,Old Mansion House, Eamont Bridge, Penrith,Cumbria, CAIO2BXTelephone: P~nrith (0768) 64771 Telex: 64326Price: £20 (including inland postage)Overseas: Surface mail £22 Air Mail £27

Previous sheet metal ductwork specificationsDuctwork Specification for High-Velocity AirSystems (Circular) 1963Standard Range of Rectangular Ducting 1967

DW/131 Sheet Metal Ductwork Specification for High-Velocity Air Systems (Rectangular) 1968

DW/121 Specification for Sheet Metal Ductwork (Low-Velocity Low-Pressure Air $ystem~)(Rectangular and Circular) - Metric 1969

DW/122B Specification for Sheet Metal Ductwork (Low-Veleocity Low-Pressure Air Systems)(Rectangular and Circular) - British 1969

DW/112 Standard Range of Rectangular Ducts andFittings - Metric and British Units 1970

DW/132 Specification for Sheet Metal Ductwork (High-Velocity High-Pressure Air Systems)(Rectangular, Circular and Flat Oval) - Metric 1970

DW/141 Specification for Sheet Metal Ductwork (Low-and High-Velocity/Pressure Air Systems)(Rectangular, Circular and Flat Oval) - Metric 1977

THIS SPECIFICATION was prepared by a Drafting Panel representing awide range of interests - ductwork contractors, general mechanicalservices contractors, consulting engineers, quantity surveyors,research associations, hospital authorities, equipment manufacturersand others. In key areas, extensive testing was carried out by theBuilding Services Research and Information Association to establishthe reliability of the provisions contained herein.

While therefore the greatest care has been taken to ensure thevalidity and reliability of the provisions in the specification, theHeating and Ventilating Contractors' Association accepts no liabilityfor the operation or performance of any of the materials, devices ormethods described herein.

In particular, HVCA does not assume any responsibility for thequality, integrity or performance of any proprietary device referredto herein.

The HVCA records its appreciation and thanks to the many personsand organisations who have freely given information on variouSaspects of this work, and in particular to the members of the DraftingPanel, who contributed ~stintingly of their knowledge andexperience.

DW1142 Drafting PanelJ. H. G. Gardner (Chairman)K. AngoodJ. Barker (part time)D. Blackstone (part time)K. J. Eatwell

OK. ElphickC. R. HiltonG. P. ManlyR. J. PittP. ScurryA. J. SimpsonH. ThomasK. T. Wheatley

W. R. Cox (Technical Consultant)J. M. Paynton (Secretary, Duct Work Group)

Contents

Part One TECHNICAL INFORMATIONTO BE PROVIDED BY DESIGNER

1 STANDARDS 22 COMPONENTS 23 SPECIAL REQUIREMENTS 2

Preface 9Foreword 10

Part Two STANDARDS4 APPLICATION 135 DUCTWORK CLASSIFICATION 136 AIR LEAKAGE STANDARDS 137 MATERIALS 14

Part Three RECTANGULAR DUCTS8 STANDARD RA!"lGE OF

RECTANGULAR DUCT SIZES 158.1 Standard range 158.2 Unusual aspect ratios 15

9 CONSTRUCTIO!"l 159.1 General....................................... 159.2 Variable airvolume systems 159.3 Sealants and gaskets 159.4 Sheet thicknesses 169.5 Longitudinal seams 169.6 Cross joints 169.7 Stiffeners 169.8 Ductwork galvanized after manufacture 219.9 Fastenings 21

10 PLAi''T CONSECTIONS 21

11 FITTINGS 3511.1 Standardisation of fittings 3511.2 General constructional requirements 3511.3 Stiffeners 3511.4 Splitters 3511.5 Turning vanes 3511.6 Twin bends 3511.7 Branches 3511.8 Change shapes 3511.9 Expansions and contractions 3511.10 Sealant 35

Part Four CIRCULAR DUCTS12 STANDARD SIZES 3913 CONSTRUCTION 39

13.1 Spirally-wound ducts 3913.2 Straight-seamed ducts 3913.3 Longitudinal seams 3913.4 Cross joints 3913.5 Fastenings 41

14 FITTINGS 4114.1 Standardisation of fittings 4114.2 Nominal diameters 4114.3 Sheet thicknesses 4114.4 Socket and spigot joints 41

Part Five FLAT OVAL DUCTS15 STANDARD SIZES AND

SHEET THICKNESSES 4916 CONSTRUCTION (SPI~~~~:~:o~;:n)······· 50

16.1 General................ • ···so16.2 Longitudinal seams .:::::::::::::::::::::: 5216.3 Cross joints 5216.4 Stiffening 52

17 CONSTRUCTION(STRAIGHT.SEAMED) .... 5118 FITTINGS

18.1 General constructional requirements. 5218.2 Standard fittings for flat oval ducts .... 52

Part Six HANGERS AND SUPPORTS(9) .. 55

Part Seven GENERAL10 ALUMINIUM DUCTWORK 6321 ACCESS OPENINGS 6422 CONTROL DAMPERS 6523 FIREDAMPERS ....•................................. 6624 BENDABLE ANDFLEXIBLE DUCTS-

METAL ........••..•........................................ 6725 FLEXIBLE DUCTS-FABRIC 6826 FLEXIBLE JOINTS 6827 SEALANTS, GASKETS AND TAPES 6928 PROTECTIVEFI1'lSHES 7029 CONNECTIONS TO BUILDER'S WORK 7130 ACOUSTIC LININGS 7131 mERMALINSULATION 71

Part Eight APPENDICESAPPENDIX A AIR LEAKAGE FROM

DUCTWORK 73APPENDIX B AIR LEAKAGE TESTISG

PROCEDURE 77APPENDIX C IDENTIFICATION OF

DUCTWORK 80APPENDIX D TRANSPORT, HA1'll>LING

ANDSTORAGE OFDUCTWORK 82

APPENDIX E DUCTWORK SYSTEMSANDFIRE HAZARDS 81

APPENDIX F GALVAi'lZING AFTERMANUFACTURE 83

APPENDIX G STAINLESS STEEL FORDUCTWORK 84

APPENDIX H PRE-eOATED STEELFOR DUCTWORK ...............• 86

APPENDIXJ ALUMINIUM Dl1CTWORK ...• 87APPENDIX K EUROVENT .........•.............. 87APPENDIXL SUMMARY OF BS2989: 1982 .. 88APPENDIX M 'DESIGN NOTES FOR

DUCTWORK' ..•................... 90APPENDIX N BIBLIOGRAPHY 90APPENDIXP CONVERSION TABLES ........• 92

Part Two STANDARDSDuctwork classification .Air leakage limits .

Part ThreeRECTANGULAR DUCTSStandard sizes .Minimum sheet thicknesses .Constructional requirements-low-pressure (up to 500 Pal .Constructional requirements-medium-pressure (up to 1000Pal .Constructional requirements-high-pressure (up to 2000 Pal .Constructional requirements-high-pressure (up to 25(0) .Ductwork galvanized aftermanufacture .Fastenings .Examples of the appl1catlon of theJoint rating system (Tables 5 to 8) ••.••.•••Fittings - standard names anddescriptions .Number of turning vanes wherer = 5Omm .

Part Four - CIRCULAR DUCTSStandard sizes .Constructional requirements-spirally·wound .Constructional requirements-straight-seamed .Permitted fastenings and maximumspacings .F!"!ngs. - sh~et thicknesses .Flttmgs - spIgots .Fittin.gs:- standard names anddescnptlons .

Part Five FLAT OVAL DUCTSStandard sizes and sheet thicknesses ....Stiffening requirements-low- and medium-pressure .Stiffening requirements -high·pressure .Fittings - standard names anddescriptions .

Part Six HANGERS ANDSUPPORTSSupports for horizontal ducts-rectangular .S~pports for horizolltal ducts - .cIrcular .Supports for horizontal ducts-flat oval .

Part Seven GENERALAluminium ducts - rectangular-constructional requirements .Aluminium ducts-circuiar-constructional requirements .Protective finishes for ductwork .Protective finishes for supportingmembers. etc .

Part Eight APPENDICESAir leakage rates .Recommended test pressures (withleakage rates) .Recommended duct identification .Examples of further identificationsymbols ..............•..........................

CIRCULAR DUCTSLongitudinGl seam

74 Grooved seam (straight-seamed ducts)

Cross joitrIs75·81 Spirally.wound duets .82-86 Straight-seamedducts .

Futings87·93 Bends .94-100 Bl"lU1chcs .

101·102 Change shapes .103·104 Transformations .105·106 Offsets •........................................107·108 Connectors .109·110 Closures .

111·113

114-117

118·120

130·131132·133

134135136

RECTANGULAR DUCTSLongitudinal seams ....•.....................Illustrations of panel stiffening .

CrossjoinuSocket and spigot (ctOSSsectional) .~ke:t and spigot (comers andJUnc:t1Ons)........••.••.•....•.....•.....•......Cleated (cross sectional) .Cleated (comers and junctions) .FlanJed (~ sectional and cornersand JIOnc:t1Ons) .Single stiffeners •..............................TIC rods .•..•.................•.................

FittingsExamples of 'hard' and 'easy' .Bends ..•........................................Branches .Offsets .Tapers .Transformations .Change shapes ..•.............................

9·1213-19

·26-242.5·323J.4J

44-4950

5152·5960-6364-6667-6976-7172·73

FLAT OVAL DUCTSStiffening (tie rod positioning)-low- and medium-pressures .S~iffening(tie rod positioning)-htgh-pressure _ .Tie rod fastening methods .

FittingsBends .....•..•.•....••..•.......................BranchD - for branches off Oat pronte.see rtcttlllgular dllClfittings. Figs. 60-62Brancha -for branches off semi·"irc:ular profile. see circular fittings.Figs. 94-/00Tapers .Transformations .Offsets .CoupliDgs ...•.................................CIosIIIa ...•......••...•.•......................

HANGERS AND SUPPORTSHorizontal duclS

137·139 Attachment to structure .140·145 Hangers .............••........................146·158 Duct supports ..•.....•.......................

159·160 VerricGl duclS ...••••••••••..•••....•....•.....

GENERAL161·166 Fire dampers ...•..............................167·168 Flexible joint connections .

APPENDICES169 Permitted leakage at various

pre5Sllla •••••.••••••.••••••••.•••••••••••..••••170 Leakage as perceinage of airflow .171 Typical leakage test apparatus .172 Example of duet identification symbol

24

2.5·2728

29·30

31·333434

424344-45

5859

59·60

61

66-6769

In our rapidly changing environment, engineering specifications needfrequent reassessment. The specification DW/141 (published in 1977) wasno exception.

This new specification DW/142 in no way minimises the wid~spreadacceptance of its predecessor as the yardstick for the manufacture andinstallation of ductwork. Constructional principles have changed little, but inorder to meet the needs of designers, a medium-pressure class has beenintroduced. Further, the requirements of energy-conscious users havenecessitated the introduction for the first time of performance levels in termsof air leakage for all classes of ductwork.

The establishment of such leakage limits does not imply that all installedductwork needs to be pressure tested. This new ~pecification ifconscientiously followed during construction and erection will produce low-leakage ductwork and will in general obviate the need for costly site testing.

The Duct Work Group of HVCA has for well over twenty years beenengaged in the compilation of specifications for the construction andinstallation of ductwork. The principles underlying this work have ever beenthat the client should obtain a reliable product, made in accordance with thebest technology available at the time, and that the specification should makeit possible for good ductwork to be made by the small firm using traditionalmethods as well as by the large firm using computers and automatedmachinery. I believe that we have succeeded in these aims, and the evidenceto support that claim is to be found in the growing acceptance and statusworldwide of the HVCA's ductwork specifications.

I would like to emphasize an important point. Just as DW/142 throws moreresponsibility on the ductwork contractor, so it does also on the designer tospecify his requirements in greater detail than he has in many instances in thepast, for both technical and contractual reasons.

It was a conscious policy of the Executive Committee of the Duct WorkGroup to consult widely in the compilation of DW /142, and the DraftingPanel therefore included not only representatives of ductwork contractors,but also of general mechanical services engineers, the hospital authorities,consulting engineers and of the industry's research association. A largenumber of other individuals and firms were consulted on specific matters.Our thanks are due to them for their interest in the work and for theirvaluable contribution to making this new ductwork specification theoutstanding work 'that it is.

My special thanks are due to Mr. W. R. Cox, our technical consultant,and to Mr. 1. M. Paynton, the Secretary of the Duct Work Group. Togetherthey have reduced to order a vast amount of raw material. As before,Mr. Paynton has been responsible for the planning, typography and designof the book itself.

R. J. Pitt,Chairman, Executive Committee,Duct Work Group, 1981/82

Since the publication of ductwork specificationDW/141 in mid-1977, the need for energy con-servation has been universally recognised, and inrespect of the HVCA ductwork specification thishas been expressed in an emphatic demand frommany quarters for ductwork with a known rate ofair leakage. This new specification therefore pro-vides leakage limits for all the ductwork coveredby it.

Enquiries among designers have shown that theclassification of ductwork used in DW/141 nolonger accords with practice, as the low-pressurespecification was being used for systems in part ofwhich maximum operating pressures exceeded 500Pa, and operating pressures above 1500 Pa werebeing avoided because of high energy cost. Theclassifications in DW/142 have therefore been ex-tended and now cover constructional require-ments and leakage limits for low-, medium- andhigh-pressure ductwork, with the high-pressureclassification in two parts so that the standard ofairtightness can be matched more closely to theoperating pressure.

Testing for air leakage remains mandatory forhigh-pressure ductwork, but is not for low- andmedium-pressure ductwork. (The testing pro-cedure in DW/142 now covers all the pressureclasses.)

Pressure the main factorPressure rather than velocity is the basis of class-

ification used in DW/142, because air leakage isalmost entirely a function of pressure, and pres-sure, not velocity, is the main factor in determiningduct strength and panel deflection.

Reappraisal of constructional and erectionrequirements

The new approach described above has necessi-tated a reappraisal of constructional and erectionrequirements in relation to performance underworking pressures.

The constructional tables in DW/141 were basedon practical experience, supplemented by the re-sults of tests commissioned by HVCA or madeavailable from other sources; and on the informa-tion provided by manufacturers of proprietarymaterials.

With the introduction of leakage limits for allclasses of ductwork, more precise information wasneeded on leakage from ductwork under pressure.In 1979 the Building Services Research andInformation Association carried out on behalf of

HVCA a series of tests designed to establish normsfor the types of longitudinal seams and cross jointsincluded in DW/141, and this work confirmed thatthe leakage limits proposed by EUROVENTcould be accepted for ductwork manufactured anderected to the requirements of DW/142.

The leakage limits for EUROVENT classifi-cations A, Band C, as set out in their Document2/2 (Air Leakage in Ductwork), have thereforebeen adopted for the low- and the medium- and forthe high-pressure Class C classifications inDW/142. Document 2/2 has no standard for aleakage class equivalent to our Class D, for whichDW/142 retains the leakage limits used in DW/141for high-pressure ductwork.

The new range of pressures required furtherinvestigation of the rigidity of cross joints and stif-fening. By using the results of tests carried out in1966by the then Heating and Ventilating ResearchAssociation (now BSRIA) on high-pressure rec-tangular ducts, the stiffness under operating condi-tions of all the I-section cross joints could be com-pared by a relatively simple testing procedure.BSRIA carried out such tests on behalf of HVCAin 1980.. With this more precise information available,

the constructional tables have been rearranged togive the limits, in terms of duct size and stiffenerspacing, for all the pressure classes.

Design function facilitatedThe inclusion ofleakage limits in relation to duct

surface area will enable the designer to allow forleakage more precisely in his calculations. This inturn will reveal what level of airtightness is neededto maintain the terminal air flow. For the air handl-ing system where the ratio of duct area to air flowfalls within the normal range, the pressure classifi-cation will establish the degree of airtightness, andthe designer will only need to specify the class. Butwhere the duct area is disproportionately large inrelation to air flow, the designer may need to callfor a higher class in order to keep total air lossthrough leakage within an acceptable figure.

Leakage limits resulting from the application ofthe formula used in the EUROvENT Document2/2 are set out in Table 2 for the three classes ofductwork A, Band C, and also for D, for whichDocument 2/2 has no equivalent. These pressure/leakage relationships are shown grap~ically onpage 75, and air loss as a percentage of air flow onpage 76. .

Contractual implications of DWI142It is necessary for all concerned with ductwork

installation to appreciate the contractual impli-cations of DW/142.

It will serve no one's interest for the specifier toshelve his responsibilities by stating: 'Ductwork tobe to DW/142' and to leave it at that. DW/142 haspedormance levels for all the pressure .bandscovered by it. The specifier must therefore clearlystate at what pressure level or levels the system isdesigned to operate, so that the ductwork con-tractor may select the appropriate constructionaldetails and not incur unnecessary manufacturingcosts. Further, as the leakage testing of low- andmedium-pressure ductwork is not mandatory, thespecifier must positively state his requirements inthis respect, as the additional complexity in rela-tion to the installation process, and the significantadditional cost, of the testing operation must beprovided for by the ductwork contractor.

DW/142 specifies a pedormance level in respectof air leakage for the ductwork alone. It does notand in the circumstances cannot specify a pedor-mance requirement for the whole of the air distri-bution system, as the numerous items of equip-ment forming part of the total air distributionsystem are not manufactured by the ductwork con-tractor, who frequently has no voice in choosingsuch equipment or knowledge of or control over itsair containment characteristics.

The ductwork contractor will therefore usuallyhave fulfilled his obligations if he is able to demon-strate that air leakage from the ductwork is withinthe limits relevant to the pressure class.

General updatingIn preparing DW/142, the opportunity has been

taken to incorporate modifications and additionsarising from the experience gained in the applica-

tion of DW/141 and of technical developmentssince the latter was published.

In order to help the designer to provide as soonas possible all the information relevant to the duct-work contract, the section 'Technical Infonnationto be Provided by Designer' has been lifted out ofthe body of the specification and transferred to aflap att&ched to the front cover.

The standardisation of names and descriptionsof duct fitting will prove of value to all concernedwith ductwork design and fabrication, particularlythe increasing number of £inns using computers intheir work. .

The provisions covering hangers and supports(Part Six) have been updated and expanded tobring this important aspect of ductwork instal-lation into line with contemporary practice.

The appendices on stainless and pre-coated steelductwork and aluminium ductwork will prove ofvalue in cases where the conditions are such towarrant the use of ductwork made therefrom.

Advice on transport, handling and storage ofductwork has been included in an appendix.

Finally, mention should be made of the newpublication of the Chartered Institution of Build-ing Services - the Design Notes for Ductwork.This for the first time has codified the availableinformation on duct design, and is a worthy com-plement to the practical constructional and install-ation provisions in DW/142.

J. H. G. Gardner,Chairman, DW1142 Drafting Panel

In this document:(1) The expressions 'low-pressure,' 'medium-pressure' and 'high-

pressure' relate to the pressure/velocity classes set out in Table 1.(2) 'Mean air velocity' means the design volume flow rate related to

the cross-sectional area.(3) Reference to the air distribution system pressure relate to the

static pressure of the relevant part of the ductwork system and notto the fan static pressure. .

(4) The symbol for litres is 'L': 1000litres per second is equivalent to 1cubic metre per second.

(5) The pascal (Pa) is the internationally agreed unit of pressure. Therelationship of the pascal to other units of pressure is: 500 pascals= 500 Newtons per square metre = 5 millibars =approximately 2inches water gauge.

(6) All dimensions quoted in this specification refer to the nominalsizes, which are subject to the normal relevant commercial andpublished tolerances.

(7) This specification includes a number of proprietary devices.Where in respect of any such device there is divergence betweenthe requirements of DW/142 and the manufacturer'srecommendations for use, the former shall take precedence.

Duct pressure classification

As the static pressure in a duct system progressively changes from the fan,economic advantage can be obtained by changing tHe duet pressureclassification to match more closely the duct distribution static pressure.

For example, some large systems could well be classified for leakagelimits as follows:

Plant rooms and risers

Main floor distribution

Low-pressure outlets

ClassC

ClassB

OassA

4 APPLICATION4.1 This specification sets out minimum require-ments for the manufacture and installation of duct-work for air distribution systems, made from anyof the materials listed in Section 7 and being withinthe limits of size and/or metal thicknesses specifiedin the relevant tables and operating at normaltemperatures within the pressure and velocitylimits specified in Table 1. The specification alsoprescribes (Table 2) the limits of air leakage for thevarious pressure classes.4.2 Unless stated otherwise, the methods and de-vices described herein apply to all the pressureclasses set out in Table 1.4.3 This specification is not intended to apply toductwork handling air which is polluted or is other-wise exceptional in respect of temperature orhumidity (including saturated air); nor is it suitablefor ductwork exposed to a hostile environment,e.g. contaminated air, off-shore oil rigs, etc. Thedesign, construction, installation, supports andfinishes in such cases should be given special con-sideration in relation to the circumstances of eachcase. This specification is also not intended toapply to domestic warm air installations.

5 DUCTWORK CLASSIFICATION •5.1 This specification is based on the pressureclasses set out in Table 1.

Duet Staticpressurelimit Mean air Airpressure velocity leakageclass Positive Negative (maximum)

1 2 3 4 5Pa Pa m/sec

Low 500 500 10 OassA

Medium 1000 750 20 OassB

2000 750 40 OassCHigh

2500 750 40 OassD

6 AIR LEAKAGE STANDARDS6.1 Limits for each pressure classPermitted air leakage is related to four standardsof airtightness, as set out in Table 2.6.2 Compatibility with EUROVENTThe leakage factors used in Table 2 for Classes A,B and C are the same as those used for the classessimilarly designated in the EUROVENT Docu-ment 2/2 (Air Leakage in Ductwork).6.3 Leakage at various pressures; and otherrelationshipsApplying the limits specified in Table 2, AppendixA (Table 31) sets out the permitted leakage at eachof a series of pressures up to the maximum for eachclass. Included in that appendix is a graphical pre-sentation of the pressure/leakage relationship; andalso charts from which may be determined leakageas a percentage of airflow for classes A, B or C.Appendix A also gives details of the basis for theleakage limits specified in Table 2.

Air leakage Leakage limit1 2

litres per second per squaremetre of duct suiface area

Low-pressur~ 0.027 x pO.6SOassA

Medium-pressur~ 0.009 x pO.6SOassB

~-pressur~ 0.003 x pO.6SassC

~-pressur~ 0.001 x pO.6SassD

6.4 Testing for air leakageAll ductwork operating at pressures classified inthis specification as 'high pressure' shall be testedto establish conformity with the relevant leakagelimits set out in Table 2. .Testing for leakage of ductwork operating withinthe low and medium ranges of pressure in thisspecification will not form part of the ductworkcontract unless this requirement is set out in thejob specification - see also Note (2) on page 1.

7 MATERIALS7.1 AppUcabilltyThis specification applies to ductwork made frommaterials as defined below, or equal. ('Sheet' is tobe understood to include coil.)7.2 Zinc-e:oated steel

7.2.1 Ductwork will normally be made fromhot-dip galvanized sheet to BS 2989, Grade Z2,coating type, or equal. If this is not available,alternative types are:7.2.2 Hot-dip galvanized sheet to BS 2989,Grade Z2 or Grade Z3, with iron-zinc alloycoating type IZ.l00 or IZ.I80, or equal.7.2.3 Cold-reduced sheet to BS 1449, GradeCR4, having a zinc coating applied by electro-plating (coating thickness 2.5 microns), orequal.

7.3 Black steelWhere black sheet is specified, it shall be cold-reduced steel sheet to BS 1449: Part 1, Grade CR4GP, or equal.7.4 Stainless steelWhere stainless steel sheet is specified, it will be

the responsibility of the designer to indicate thetype most suitable for the conditions in which theductwork will be exposed. In doing so, it is recom-mended that the factors set out in Appendix Gshould be taken into account. In this connection,regard should be had to BS 1449: Part 2, whichincludes stainless steel sheet and strip.7.5 Pre-coated steelIf the designer for aesthetic or other reasons speci-fies the use of pre-coated steel for the ductwork, heshould consider the availability of the material andthe restrictions on fabrication methods - seeAppendixH.7.6 AluminiumWhere aluminium sheet is specified, it will be theresponsibility of the designer to indicate the typemost suitable for the conditions to which the duct-work will be exposed. In so doing, regard shouldbe had to BS1470 for aluminium sheet and BS1474 for aluminium section. (See Section 20 hereinfor constructional requirements for ductworkmade from aluminium sheet, and Appendix J forsome general notes on the ml!-terial.)

Part Three - Rectangular Ducts

8 STANDARD RANGE OF RECTANGULARDUCT SIZES8.1 Standard rangeTable 3 represents the range of standard sizes ofrectangular ducts which at the time of preparingDW/142 were being processed by the InternationalStandards Organisation as an ISO Standard.(Note. - The sizes in Table 3 are the same as thosein Table 10fDW/141.)8.2 Unusual aspect ratiosDuct sizes with an aspect ratio greater than 4:1 arenot recommended. Although they offer no pro-blems of construction, they increase frictional re-sistance and the possibility of noise.

gular ductwork have been established following.independent tests, the limits of use being related tothe characteristics of rolled steel angle. (See 9.5 forlongitudinal seams, 9.6 for cross joints and 9.7 forstiffeners. )9.2 Variable air volume systemsThe requirements for sheet thickness and stif-.fening set out in the relevant tables shall, unlessotherwise specified by the designer, apply to duct-work for YAY systems (see also 3.8 in Part One-Technical Information to be Provided by Designer- inside flap).9.3 Sealants and gasketsSpecial attention is drawn to the requirements forthe use of sealants and gaskets, as the case may be,in relation to the various longitudinal seams andcross joints included in this specification. (Section27 sets out the desirable characteristics of sealants,gaskets and tapes.)

9.1 GeneralThe main constructional requirements for rectan-

Long side Short side (mm)(mm) 100 150 200 250 300 400 500 600 800 1000 1200

150 0.50 0.60

200 0.60 0.70 0.80

~0.70 0.80 0.90 1.00

" 300 " 0.80 0.90 1.00 1.10 1.20I 400 1.00 1.10 1.20 1.30 1.40 1.60

500 1.30 1.40 1.50 1.60 1.80 2.00

600 1.50 1.60 1.70 1.80 2.00 2.20 2.40

800 2.00 2.10 2.20 2.40 2.60 2.80 3.20

1000 2.50 2.60 2.80 3.00 3.20 3.60 4.00

1200 3.00 3.20 3.40 3.60 4.00 4.40 4.80

1400 3.60 3.80 4.00 4.40 4.80 5.20

1600 4.00 4.20 4.40 4.80 5.20 5.60

1800 4.60 4.80 5.20 5.60 6.00

2000 5.00 5.20 5.60 6.00 640

9.4 Sheet thicknessesMinimum sheet thicknesses related to duct longerside and to pressure classification are given inTable 4. (This information is also included inTables 5 to 8.)

Table 4 Minimum sheet thicknesses -Rectangular ducts

Maximum Sheetthicknessduct size Low-and(longerside) medium- High-

pressure pressureducts ducts

1 2~OAl 3 \\.\>'i.tlfl"2..i\oo 'Qi

mID mm mID400 0.6 0.8

600 0.8 0.8800 0.8 0.8

1000 0.8 0.8

1250 1.0 1.0

1600 1.0 1.0

2000 1.0 1.2

2500 1.0 1.2

3000 1.2 -

9.5 Longitudinal seams9.5.1 Types availableLongitudinal seams are illustrated in Figs. 1 to7. The limits of use, if any, are given with theindividual illustrations.9.5.2 Sealant in longitudinal seamsSealant shall be used with aU longitudinalseams, irrespective of the pressure class. Thesealant may be included in the seam during.manufacture or be applied as edge sealant.9.5.3 Welded seamsAs the exception to the requirements of9.5.2, awelded seam is acceptable without sealant, pro-vided that the welding is continuous.

9.6 Cross joints9.6.1 Cross joint ratingsFor cross joints, a system of rating has beenused to define the limits of use. The rating foreach cross joint is given with its drawing, andthe limits applying to that rating, in terms ofduct size longer side and maximum spacing, aregiven in Tables 5 to 8. Other limits on use aregiven with the individual drawings.

The system of ratings is as follows:Socket and spigot joints - Al to A3 (Figs. 9to 12)Cleated joints - Cl to C4 (Figs. 20 to 24)Flanged joints - Jl to J6 (Figs. 33 to 43)

9.6.2 Comers and junctionsSocket and spigot joint comers and junctions

are illustrated in Figs. 13 to 19.Cleated joint comers and junctions are illus-trated in Figs. 25 to 32.Details of the comer treatments of flangedjoints are included with their illustrations- Figs.33 to 43.9.6.3 Sealant in cross jointsSealant shall be used between sheet and sectionin all cross joint assemblies.With cleated joints, the sealant shall be appliedduring or after the assembly of the joint.With socket and spigot joints made on site,sealant shall be applied during or after assemblyof the joint. It is permissible to use chemical-reaction tape or heat-shrink strip (but not con-tinuous band) as alternative methods of sealing,provided that close contact is maintained overthe whole perimeter of the joint until the joint iscompleted.With all ft8nged joints, the sealant betweensheet and section should preferably be incor-porated during construction at works, but edgesealant is acceptable. The joint between sec-tions of ductwork is then made, using an approv-ed type of sealant or gasket (see Section 27).

9.7 Stiffeners9.7.1 GeneralStiffeners shall be applied so that the truerectangular cross-section of the duct ismaintained.9.7.2 External stiffenersThe sections (including proprietary flanges)suitable for use as single stift'eners have beengiven a rating from S1 to S6 in terms of duct sizelonger side and maximum spacing. The ratingsare specified with the illustrations of the stif-feners, Figs. 44 to 49, and the limits of use aregiven in Tables 5 to 8. The girth stiffeners forsocket and spigot joints covered in Fig. 12 arealso applicable to girth stiffeners in general.9.7.3 Internal stift'enersTie bars connecting the flanges of cross joints orintermediate stiffeners are the only form ofinternal stiffening for rectangular ductworkcovered in this specification. (For the use of tiebars in flat oval ductwork, see 16.4.) Otherforms of internal stiffening or bracing are notrecommended.The use of tie bars in rectangular ducts shall beauthorised by the designer; and if circumstancesrequire the use of internal stiffening in any otherform, the method to be used shall be approvedby the designer.Alternative methods of attachment of tie barsare shown in Fig. 50.

Examples of the appUcationof the joint and stiffenerrating system are given onpages 21and 23.

Longitudinal seams

For permitted fastenings (typesand spacing), see Table 10 (page 21)

Alternative sealant locations

\1 I.rH····I~

Fig. 2 Grooved corner seam\

Alternativesealantlocations

~Alternativesealantlocations

Fig. 4 Button punch snap lock seam

Alternativesealant locations

INote.-Thisseam is accept-able for useon low-andmedium-pressureducts only

Fig. 5 Standing seam (intemal or external)Minimum height IS mm

Alternativesealant Fasteninglocations ./

~-'-Fig. 6 Capped standing seam (internal or

extemal)Minimum height ISmm

Alternative sealantlocations

Note. - This seam is acceptablefor use on low- and medium-pressure ducts only

Constructional Requirements - Rectangular DuctsTable 5 LOW PRESSURE (up to 500 Pal

Maximum duct size(Ionger"side)or--+ 400 600 800 1000 1250 1600 2000 2500 3000length of stiffeners •

Minimum sheet 0.6 0.8 1.0 1.2thickness--+Type Rating Sheet Maximum spacing between jointsand stiffenersI 2 3 4 5 6 7 8 9 lO II 12III PS 3000-=-= Al ......_- .............. ..............••....... _ ...., ~ SS 3000-=CoD PS 3000 2000 1600 1250'a, :\2 ...•.................... .... _ .................... ..-.....................• ............ _ ............ ........................... ~C/) SS 3000 3000 1600 1250~- PS 3000 2000 1600 1250 jlooo 1 800~~~ A3 ........................ ....................- ..__ .-......._ ...... ..._ .....................

SS 3000 3000 2000 1600 1250 800PS 3000 1600 I I ICl ........ _ .............. .................. __ .. ....._ .........•.........SS 3000 3000

III PS 3000 2000 1600 1250-='S C2 .........•.......•...... .................... _-- ..._ ....•................ .......................... ............................., SS 3000 3000 2000 1250~~ PS 3000 2000 1600 1250 1000C;~ C3 _ ................ -.- .__ .....-.......- -_..._ ................ ........•.•..........•.... ......•................... ...........................u SS 3000 3000 1600 1250 1000

PS 3000 3000 1600 1250 1000 800C4 .•...•.......••..•...••. ....-...__ ..-...... ......__ ................ .......................... .......................... .......................... ........ _ ...._ ...........

SS 3000 3000 2000 1600 1250 800PS 3000 1600 1250 625

JlISI ........................ ...........•...__ .. .......................... .......................... ...........................·SS 3000 3000 1250 625

~ PS 3000 2000 1600 1250 625J2IS2 ........................ ......_ ............ -._. ..-...._ ....._ ....._ .. .......................... .......................... ..........................~ SS 3000 3000 1600 1250 625=

~ PS 3000 2000 1600 1250 1000 800-C/) J3/S3 .........._ ..........•. •........••_ ......._ .... .......................... .......................... .......................... ............ _ ............ ........_ ................~ SS 3000 3000 2000 1600 .1250 800III-= PS 3000 2000 1600 1250 1000 800 800Q J4/S4 ..................•..... ........__ ........_ .. _ ........................ ...........•........•..... .......................... .................... _ .... ........_ ................ .................... -.......,

SS 3000 3000 2000 1600 1250 1000 800~~CoD PS 3000 2000 1600 1250 1000 800 800 800 625=••~ J5/S5 ........................ ..............._-_ .. ..._ .........-...._ .... .......................... .•........................ ._ ................. -.... ......................•... ......_ ...._ ........•... ...•............-._ .... _ .._ ..--SS 3000 3000 2000 1600 1250 1000 800 800 800PS 3000 2000 1600 1250 1000 800 800 800 800

J6/S6 .................•.. _ .. ............._.__ .. ..._ .••.............•..- . ....................... .......................... .......................... ........_ ................ .......... __ ............ ..._._ ......._ ...._ .. ....__._-SS 3000 3000 2000 1600 1250 1000 800 800 800

NotesIn the constructional tables 5 to 8:(l) The joints and stiffeners have been rated in terms of duct longer side and maximum spacing - see 9.6.1 for

joints and 9.7.1 for stiffeners.(2) In CoI. 3:

'PS' = plain sheet;'SS' = stiffened sheet, by means of:(a) beading at 400 mm maximum centres: or (b) cross-breaking within the frame fonned by joints and/or.stiffeners: or (c) pleating.

Constructional Requirements - Rectangular DuctsTable 6 MEDIUM PRESSURE (up to 1000Pal

Maximum duct size(longerside)or - 400 600 800 1000 1250 1600 2000 2500 3000lengthofstiffeners

•l\'finimumsheet 0.6 0.8 1.0 1.2thickness-Type Rating Sheet Maximum spacing between jointsand stiffeners

1 2 3 4 5 6 7 8 9 10 11 12:II P5 3000~ Al ......••...•.•...... _ .. .................... -....., SS 3000-~ PS 3000.s.:I'l A2 ............ -........•.. .................... _ ...~ SS 3000;:: PS 3000 1600 1250 1000 800.:.lit A3 ...-..............••••.. .......... ............... .....•...............•.• - .•........................ ..........•..•__ ..-.. ...._-_._-~ SS 3000 3000 1600 1250 800

PS 3000CI ........................ ....~....................

55 3000~ PS 3000 1600.: C2 ........................ ................ _ ........ ............. _ ...........~ S5 3000 3000·'1:l~ PS 3000 1600 ••-;~ C3 .... -................... ...._.- ...__ ....-.... .............•............0 5S 3000 3000

PS 3000 1600C4 ........................ .................... -.... ........-.•..............

S5 3000 3000P5 3000 1250 625

J1I51 ........•............•.. ........•..........•...... .............•............ ..........................S5 3000 1250 625

'" PS 3000 1250 1250 625~ J2/52 .............. _ ........ ...._ •....•.............. ........................ - .......................... ............••.•••........~= SS 3000 1600 1250 625~~ P5 3000 1600 1250 1000 800:I'l

~ J3/53 .............. _ ......•. ...._ .................... ........... __ ........... .......................... ......•.......•.._ ...... ...._-_.~ 55 3000 3000 1600 1250 800.; P5 3000 1600 1250 1000 800 800.:; J4/54 ........................ .... _ ........•...•....•.. ........_ ................ .......................... .......................... ...._.__ ._.._ .. ."-"'-_._''1:l S5 3000 3000 1600 1250 1000 800~:£= P5 3000 1600 1250 1000 800 800 800 625~,... J5/55 ........................ .......•.................. .......................... .......................... .......................... ...._ ....._._.__ .. ........ _ ...._ .......... ..........._._-- .. ................. \ .........•. 55 3000 3000 1600 1250 1000 800 800 800

PS 3000 1600 1250 1000 800 800 800 800 625J6/56 ......................•. ...........•.•..••........ .......................... .......................... .......................... ...._ ...__ ......_ .... .......................... ......•••........•.••..... .......................... ............••...........

S5 3000 30QO 1600 1250 1000 800 800 1100 625

(3) Limits of length of single stiffeners apply to opposed side (transverse) stiffeners and to longitudinalstiffeners: also to girth stiffeners, irrespective of comer treatment. .

(4) With longitudinal stiffeners, maximum spacings apply both between stiffeners and ~m stiffeners toduct edges.

(5) The choice of lagging may be limited with stiffened panels.(6) For ductwork galvanized after manufacture, see 9.8 and Table 9.

Constructional Requirements - Rectangular DuctsTable 7 HIGH PRESSURE (up to 2000 Pal

Maximum duct size(lonfhr side) or-+ 400 600 800 1000 1250 1600 2000 2500lengt of stiffeners

Minimum sheet 0.8 1.0 1.2thickness_

Type Rating Sheet Maximum spacing between joints and stiffeners

1 2 3 4 5 6 7 8 9 10 JJCIl Al PS/SS 3000-~.=_Q~., A2 PS/SS 3000..:.c-

~~ .CI)'Q. A3 PS/SS I 3000CI)-

~ JIISI PS/SS 3000 625~=5 J2/S2 PS/SS 3000 1250 800-CI)

~ J3/S3 PS/SS 3000 1250 1250 800CIl- 1250/= J4/S4 PS/SS 3000 1250 1250 800'S.,'C J5/S5 PS/SS 3000 1250 1250 1250 800 800 625~

CIQ=~J6/S6 PS/SS 3000 1250 1250 800 800 800~ 1250 . 625

Constructional Requirements - Rectangular DuctsTable 8 HIGH PRESSURE (up to 2500 Pal

Maximum duct size(lonfhr side) or - 400 600 800 1000 1250 1600 2000 2500lengt of stiffeners

Minimum sheet 0.8 1.0 1.2thickness_

Type Rating Sheet Maximum spacing between joints and stiffeners

1 2 3 4 5 6 7 8 9 10 JJCIl Al PS/SS 3000-~.=_Q~ ., A2 PS/SS 3000.:.c _

~~CI) .- A3 PS/SS 3000c.

CI)

~ JIISI PS/SS 3000 625~=~ J2/S2 PS/SS 3000 1250 625~-CI)

~ J3/S3 PS/SS 3000 1250 1000 625CIl

-= J4/S4 PS/SS 3000 1250 1000 800 625'S.,'C J5/S5 PS/SS 3000 1250 1000 800 625 625~

CIQ=~ J6/S6 PS/SS 3000 1250 1000 800 625 625 625 500ti:

9.8 Ductwork galvanized after manufactureTable 9 (which is applicable to' the low- andmedium-pressure classes only) sets out the recom-mended sheet thicknesses and stiffening for duct-work galvanized after manufacture. (See alsoAppendix F.)Table 9 Ductwork galvanized after manu-

facture (low- and med. pressureonly)

Maximum Recom- Fig.33 F~.44 Maximumduct size mended joint sti ener spacing(longer sheet rating rating filij0intslside) thickness s eners

1 2 3 4 5mm mm nun nun nun

400 1.2 13 S2 3000-

1000 1.6 J4 S3 1250

1600 1.6 J5 54 800

2000 1.6 J6 S5 800

9.9 Fastenings9.9.1 Permitted types and maximum centresTables 10 sets out the permitted fastenings andthe maximum spacings for lowe, medium- andhigh-pressure rectangular ducts. All duct pene-trations shall be sealed.9.9.2 RivetsManufacturers' recommendations as to use,size and drill size are to be followed. Rivetsresulting in an unsealed aperture shall not beused.9.9.3 Bolts and nutsBolts and nuts shall be of mild steel, protected

Table 10 Fastenings - Rectangular Ducts

by electra-galvanizing, Sherardizing, cadmiUm-plating, or other equal and approved finish.9.9.4 Self-tapping screwsSelf-tapping screws, while not recommended,are acceptable in circumstances in which the useof other types of fastening is not practicable.9.9.5 WeldlngorsheetThe suitability of welding for sheet-ta-sheetfastening will be governed by the sheet thick-ness, the size and shape of the duet or fitting andthe need to ensure airtightness. Welded jointsshall provide a smooth internal surface and shallbe free from porosity. Distortion shall be keptto a minimum.Areas where the galvanizing has been damagedor destroyed by welding or brazing shall be suit-ably prepared and painted internally and exter-nally with zinc-rich or aluminium paint.

10 PLANT CONNECTIONS10.1 DefinitionThe term 'plant connection' refers to the sheetmetal enclosure joining the components of anair handling assembly and connections betweenthe assembly and the ductwork system.10.2 Constructional requirementsThe maximum operating pressure of the plantshall determine which constructional require-ments and leakage limits are applicable to plantconnections.Where access to plant requires entry into theduct, a floor plate connected to the stiffenersshould be included so as to prevent local over-loading of the sheet metal. If-local conditionsrequire heavier construction, the designershould specify appropriately.

Sheet to sectionSheet to sheet (minimum two per side)

Maximum distance from comers 50 mmType Longitudinal seams Cross Cross joints Angle

of joints stiffeners forfastening socket and

Lap Standing Socket Rolled All slide- spigot jointsand cjfped and spigot steel flanges on flanges and all

stan 109 and flange intermediatecleats stiffeners

1 2 3 4 5 6 7

mm mm mm mm mm mmMechanically

300 60 150 300 150closed rivets 60

Bolts and nuts - - - 150 300 -Lock bolts - 300 - 150 300 300

Spot welds 30 150 - 75 300 150

Dimpling - 150 - - 150 -

EXAMPLES of the application of the joint rating system(Tables 5 to 8)

Fig. 9 - Plain socket and spigot jointThis joint is rated in Fig. 9 as A 1 for all pressureclasses, with duct size limited to 400mm longer side.The tables show that such joints by themselves giveadequate stiffening, whether the sheet itself isplain (P) or stiffened (5), provided that they arespaced at not more than 3000mm.

FIg. 24 - Angle-reinforced double-standing hem-med "S' cleatThis joint is applicable to the low-pressure classonly, and with a 25 x 3 mm angle is rated C3.Table· 5 limits the use of a C3 joint to ducts withlonger side not exceeding 1250 mm, and suchjoints give adequate stiffening at the maximumspacings specified (Cols. 4 to 8 of Table 5), thespacings varying according to whether the sheetitself is plain (P) or stiffened (S).

Figs. 41 and 42 - Slide-on FlangesThese joints are applicable to all the pressureclasses, and with a height of 30 mm are rated as 13.For medium-pressure duets, Table 6 limits the useof a 13joint to ducts not exceeding 1250mm longerside, with joints at 800 mm maximum spacing,whether the sheet itself isplain (P) or stiffened (5).Where joints are more widely spaced, inter-mediate stiffeners with an 53 rating (see Figs. 44 to49) will be necessary to meet the maximum spacingrequirements.

Application to individual ductwork contractor'sworking methodsThe individual ductwork contractor will normallyapply the rating system to his own requirements bymaking up tables covering the joints used by him.The foll<;>wingare some examples.

Duct size MaximumspacingbetweenDuet sheet joints and stiffenersthickness longerside Fig.No.or lengthof Plain Stiffenedstiffener sheet sheet

1 2 3 4 5

mm mm mm mm

0.6 400 9 and 10 3000 3000

0.8 600 11 and 12 2000 300025 mm angle

11 and 120.8 800 25 mm angle 1600 1600

30mm angle 1600 2000

11 and 120.8 1000 25 mm angle 1250 1250

30mm angle 1250 1600

1.0 1250 11 and 12 1000 125030mm angle

1.0 1600 11 and 12 800 80030mm angle

Example 2 FLANGE JOINJ as Fig. 41 or 42 for LOW·PRESSURE DUCTS

Duet Duct size Aanged RS flange ProfileMaximum spacing between

sheet longer side joint (Fig. 44) (Figs. 45 to 4'!t joints and stiffenersthickness or length of (ftange used as used as Plain Stiffenedstiffener Hsize) stiffener (H) stiffener (H) sheet , sheet

1 2 3 4 5 6 7.mm mm mm mm mm mm mm

0.6 400 20 - - 3000 3000-

0.8 600 20 25 30 2000 3000

0.8 800 20 25 30 1600 160030 30 40 1600 2000

0.8 1000 20 25 30 1250 125030 30 40 1250 1600

1.0 1250 20 25 m 625 62530 30 _ 1000 1250

1.0 0600 30 30 40 800 80040 40 - 800 1000

1.0 2000 40 40 - 800 800

1.0 2500 40+ 50 - 800 800tie bar

1.2 3000 40+ 50 - 625 800tie bar

Beading (may alsobe along theduct)

Cross breaking betweenjoints or stiffeners

Socket and spigot cross jointsNote - Particular care must be taken

in the sealing of these joints

Fig. 9 PlainAlternative sealant locations '\ Fastening

I

Fig. 10 AdjustableAlternative sealant locations Fastening" ,

Fig. II Angle reinforced(opposed sides)

FasteninlZ\~ Alternative sealant locations1\

Fasten~Alternative sealant locations

\ \ F;stening

Anglesize

For permitted fastenings (types andspacing), see Table 10 (page 19)

Rating Pressure Nclasses otes

LowAl Medium

High

LowAl Medium

High

LowMedium

LowMedium

Applicable only whereduct shorter side is lessthan400mm

Stiffeners shown inFigs. 4S to 49 arepermissible if providedwith rigid corners

Socket and spigot joints.- corners and junctions

Comers notched and closed by dressing.Alternatively. comers may be indented.

Return cut away at each half seam for lengthof spigot to leave overlap.

Seam compressed at socket to provide a flatside internally.

An adjustable socket and spigot joint asFig. 10 can be formed by extending the lengthand welding all four comers of the spigot.

With high-pressure ductwork, spigotcomers shall be welded.

Comers notched and closed by dressing.Alternatively, the comers may be indented.

Inside of lock form cut back for length ofspigot.

Joggle to accommodate lock form at socketend. Alternatively, the lock form may becompressed to provide a flat side tosocket internally.

An adjustable socket and spigot joint asFig. 10 can be formed by extending the length.and welding all four comers of the spigot.

With high-pressure ductwork, spigotcomers shall be welded.

Comers notched and closed by :iressing.Alternatively, the comers may be indented.

Outside of lock form cut back for length ofspigot.

Joggle to accommodate lock form at socketend. Alternatively, the lock form may becompressed to provide a flat side to socketinternally.

An adjustable socket and spigot joint as Fig. 10can be formed by extending the length andwelding all four comers of the spigot.

With high-pressure ductwork, spigotcomers shall be welded.

Comers notched an.d closed by dressing.Alternatively. the comers may be indented.

Inside of lock form cut back for length ofspigot.

Joggle to accommodate lock form at socketend. Alternatively. the lock form may becompressed to provide a flat side tosocket internally.

An adjustable socket and spigot joint asFig. 10 can be formed by extending the lengthand welding all four comers of the spigot.

With high-pressure ductwork. spigotcomers shaH be welded and lap seamsection sealed.

Comers notched and closed by dressing.Alternatively, the comers may be indented.

Standing double edge cut back andstanding single edge flattened forlength of spigot to provide overlap.

Seam must be positioned so that it cannotcollect or retain water.

An adjustable socket and spigot joint as Fig. 10can be formed by extending the length and weldingall four comers of the spigot if not indented.

With high-pressure ductwork, spigotcomers shall be welded.

Fig. 18 Standing seam (Internal)(see notes to Fig. 17)

Fig. 19 Capped standing seam(internal)

(Notesto Fig. 17also apply)

Cleated cross joints

TypeThick-

Rating Pressure Notesriess classes

Fig. 20 'C' cleat mmUsed on all four sides: or on opposedsides in combination with 'S' cleat.For intersection with grooved seamsee Fig. 25.~ Low For intersection with Pittsburgh lock.0.8 Cl

~7 Medium grooved comer or button punch snaplock seam. see Fig. 27.For folded comer detail.see Figs. 28 and 29.

Sealant

Fig. 21 Standing 'C' cleat I

Fastening Used on all four sides: or on opposed

/ sides in combination with 'S' cleat.- 0.8 C2 Low Fastened at comers and intermediatelyMedium at 200 mm centres maximum spacing.

Sealant Sealant For comer detail. see Figs. 30.31. and 32.~I':!!~

Fig. 22 Hemmed '5' cleatUsed on opposed sides in combinationwith 'C' cleat. May be used on all four-\i;Sui ••• -:J sides if fIxed to duct by mechanicalfasteners at 300 mm maximum centres.

0.6 Cl Low For comer detail. see Figs. 27 and 29.. -r For intersection with grooved seam.see Fig. 26.

Fig. 23 Double standinghemmed '5' cleat Used with 'C' cleat or standing 'C cleat

on opposed sides. May be used on allfour sides if fIxed to duct by mechanicalfasteners at 300 mm maximum centres.

0.8 C2 Low For comer details of 'S' cleat,Sealant Sealantsee Figs. 27.29 and 31.\- " For intersection with grooved seam.

~ see Fig. 26.~

Fig. 24 Angle-reinforceddouble standing 0.8 Used with 'C' cleat or standing 'C cleathemmed '5' cleat with: on opposed sides. May be used on all

~~~LJ25x3 C3 Low four sides if fIxed to duct by mechan\calangle fasteners at 300 mm maximum centres.

For comer details of'S' cleat.4Ox4 C4 Low see Figs. 27. 29 and 31.

Sealant angle For intersection with grooved seam."" see Fig. 26.

iI

'-~:'=O-'

Cleated cross joints - corners and junctions

Sections cut awayto show assembly

Applies aisoto all thestanding 'S'cleats

Sections cut away-to show assembly

Applies also tostanding 'C'deats

Fig. 27 'S' and 'C' cleat with Pittsburgh lock, groovedcorner or button punch snap lock seam

Notes:1. With 'C' cleats on allfour sides, three comersare as (b); the fourthoverlapped as illustratedfor 'S' cleat (c).2. (a) and (c) apply alsoto all the standing 'S' cleats

'C' cleat withextended endturned over andfixed to 'S' cleat

Oeats cut backto show ducttreatment

For comertreatments.see Fig. 27.

Oeats cut backto show assembly

'C' cleat withextended end andturned over, insertedinto adjoining 'C'cleat and fixed

Fig. 29 'S' cleat and 'C' cleat with foldedcomer

Oeats cut backto show ducttreatment

Applies alsoto all thestanding 'S'cleats For comer

treatments.see Fig. 27.

Cleated cross joints - corners and junctions (continued)

Fig. 30 Standing 'C' cleat

(treatment for three comen;for fourth comer; see Fig. 31)Applies also to a combinationof standing and plain 'C' cleats

Fig. 31 Combination of standing 'C' cleatand '5' cleat

Comer sealingclip insenedinto 'C' cleatand fastened to'S'cleat ~

Applies also to allthe standing'S' "1'cleats

"l-tFastening

Fig. 32 Standing 'C' cleat(alternative comer treatment to Fig. 30)Ranges of 'COcleats extendedand fastenedtogetner

i-

fFastening

Flanged cross joints

Fig. 33 Rolled steel angle-flanged joint, with weldedcorners

Gasket orsealant

Fig. 34 Reinforced flangecleat with 'C' cleat

5)Gasket or

/sealantFastening,;

" ;: tAlternative __ ~ ~ __ J'Alternativesealant 'S I' . jI sealantlocations ea mg clips" locations

Fig. 35 Integral flange withspring clips

GaSket/

Fig. 36 Integral standingflanged with 'C' cleat orstanding 'C' cleat

25 x330x44Ox450x5

Withplaincleat

25 high

Withstanding

cleat46 high

J3J4J5·'J6

LowMediumHigh

LowMedium

LowMediumHigh

LowMediumHigh

LowMediumHigh

Duct ends turned up 10 mm.Fixing bolts required ateach comer and intermediatelyat 150 mm centres.

Corners of flangecleats extended toprovide boltedcorner

Cleats cutback to showassembly

Flanged cross joints (continued)·

Type Dimen- Rating Pressuresions classes

Fig. 37 Attached flange

25 xO.8 12LowMedium

~Fastening Fastening

\' I

\ t ISealant Gasket Sealant

Fig. 38 Slide-on flange withintegral gasket

~ ~Alternative Sealant Locations

f tAlternativesealantloc:ations

, \Alternativesealantlocations

Fig. 40 Slide-on flange withintegral sealant

Fastening\. Fastening

i~ 'f ~Alternative Sealant Locations

LowMedium

LowMedium

LowMedium

LowMedium

LowMedium

LowMediumHigh

I

: l

V, I

N' i

~~

Corner piece."'-... ~ locked in

~....-- position by:' ~ ... , indenting

flange section

Comer pieceshape to-:nclose duetcomer

iI· ForducJcd sides overI 4OOmm., intennediateI clamps are

required at4OOmmmaxi-mum spacing

Single stiffenersDimensions and ratings

Hmm

Thicknessmm

S2

S3S4-SSS6

SlS2

S3

S4

I:--40

1.61.61.6

2.0

11 II I I I:-25-:-25-:-25-:

1.21.2

1.61.6

2.0

0.81.01.2

T:' rod.nachcd ~Gasketstiffener or 10one ancaJuIl•••JIefJuIae .1 acbjoont. Welil U'IIlIIIdtie rod imide cIuctloroma'"

11 FITTINGS11.1 Standardisation ornttings .The names and descriptions of rectangular ductfittings as set out in Table 11 are recommended foradoption as standard practice, as being in the inter-ests of designers, quantity surveyors and ductworkcontractors, and of those using computers in duct-work design and fabrication.Bends are designated as 'hard' or 'easy', and theseterms as used herein have the following meanings:

'Hard' signifies rotation in the plane of thelonger side of the cross section.'Easy' signifies rotation in the plane of theshorter side of the cross section.

An example illustrating these terms is given in Fig.51.

Fig. 5 I Bends - examples of 'hard' and'easy'

11.2 General constructional requirementsThe minimum metal thicknesses specified in Table4 apply to duct fittings. In all cases the largerdimension shall determine the sheet thickness andstiffening. Where fittings are to be galvanized aftermanufacture, the requirements of Table 9 willapply.11.3 StiffenersThe flat sides of fittings shall be stiffened in accor-dance with the construction tables 5 to 8. On theflat sides of bends, stiffeners shall be arranged in aradial pattern, with the spacing measured alongthe centre line of the bend.11.4 SplittersSplitters shall be attached to the duct by bolts ormechanically-closed rivets (or by such other fixingas can be shown to be equally satisfactory) at 100mm maximum spacing.11.5 Turning vanesSquare bends shall be fitted with turning vanes,which shall be securely attached at each end eitherto the duct or to internal runners and the runnersfastened to the duct by mechanically-closed rivetsor bolts at 150mm maximum spacing.

For single-skin vanes, the maximum length be-tween supports shall be 615 mm, and for double-skiDvanes the maximum length between supportsshaD be 1250mm.The recommended minimum number of turningvanes is given by the formula:

Nl.SW

o. = -- (see Fig. 55)r

An inner face radius of 50 mm is commonly used,and Table 12 gives the minimum number of suchvanes for the standard widths of rectangular ductsset out in Table 3.11.6 Twin bendsFor examples of twin bends, see Figs. 56 to 58.Turning vanes in twin bends in which the widths ofthe straight section and branch differ shall be set sothat the leading and the trailing edges of the turn-ing vanes are parallel to the duct axes.

11.7 BranchesA branch should be taken off a straight section ofduct, not off a taper. Branches should be con-nected to the main duct as follows:

11.7.1 Branches ror low- and medium-pressureductsConnection of branch to duct may be by cleats,rivets or bolts, and sealant shall be used be-tween duct and branch.11.7.2 Branches ror high-pressure ductsDucts shall be stiffened as necessary to take thebranch connections, and the joints made byrivets or bolts, with sealant between duct andbranch.11.7.3 WeldingAs an alternative to the methods described in11.7.1 and 11.7.2, branch connections may becontinuously welded.

11.8 Change shapesWhere a change shape is necessary to accommo-date the duct and the cross-sectional area is to bemaintained (Fig. 72), the slope shall not exceed221h0 on any side. Where a change in shape in-cludes l\ local reduction in cross-sectional area(FIB. 73), the slope should not exceed 150 on anyside and the reduction in area should not exceed 20percent.11.' Expansions and contractionsWhere these are required, an expansion shall bemade upstream of a branch connection and a con-traction downstream of a branch connection. Theslope of either an expansion or a contractionshould not exceed 221/20 on any side. Where thisangle is not practicable, the slope may be increas-ed, providing that splitters (Fig. 68) are positionedto bisect the angle between any side and the centreline of the duct.11.10 SealantSealant shall be used in all longitudinal seams andcross joints of fittings. Sealant shall be to the re-quirements of Section 27.

Table 11 RECTANGULAR DUCT FITTINGS-STANDARD NAMES AND DESCRIPTIONS

Name and description Fig. No.

1 2

Bends

Shortradius-'W' up to 300 mm all angles .. .. .. .. .. .. .. .. '. .. .. 52{a)Short radius- oW'over 300 mm (all angles) .. .. .. .. .. .. .. .. .. ,. 52(b)

Medium radius (all angles) .. .. .. .. .. .. '. .. ., .. .. .. .. .. 53Long radius (all angles) .. '. .. .. .. .. .. .. .. " .. .. .. .. .. 54Square (with turning vanes) .. .. .. .. .. .. .. .. .. .. .. .. .. .. 55Twin radius - equal (all angles) .. .. .. .. .. .. .. .. .. .. .. .. .. 56Twin radius - unequal (all angles) .. .. .. .. .. .. .. .. .. .. .. .. 57Twin square (with turning vanes) .. .. .. .. .. .. .. .. .. .. .. .. .. 58Branch (all angles) .. .. '. .. .. .. .. .. .. .. .. .. .. .. .. .. 59

BranchesRectangular or circular (90°) " .. .. .. .. .. '. .. .. .. .. .. .. .. 60

Rectangular or circular (all angles other than 90°) .. .. .. ,'. .. .. .. .. 61Shoe (rectangular or circular) .. .. .. .. .. .. .. .. .. .. .. .. .. 62Shoe (high pressure) - rectangular .. .. .. .. .. .. .. .. .. .. .. .. 63

OffsetsAngled .. .. " .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 64

Mitred .. .. .. .. .. .. .. .. .. .. .. .. ,. .. .. .. .. '. .. 65

Radiussed .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 66

TapersConcentric (without splitters) '. .. .. .. .. .. .. .. .. .. .. .. .. 67

Concentric (with splitters) " .. .. .. .. .. .. .. .. .. .. .. .. .. 68Eccentric, , .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 69

Transformations

Rectangular to circular (concentric) .. .. .. .. .. .. .. .. .. .. .. .. 70

Rectangular to circular (eccentric) .. .. .. .. .. .. .. .. .. .. .. .. 71

Change shapesCross-sectional area retained .. .. .. .. .. .. .. .. .. .. .. .. .. .. 72

Cross-sectional area reduced .. .. .. .. .. .. .. .. .. .. .. .. .. .. 73

Part Three - Fittings for rectangular duetsFor sealing requirements, see Sec. 11.10 (page 33)

BendsFig. 52(a) Shortradius - 'W' up to300 mm (all angles)

Fig. 52(b) Shortradius - 'W' over300 mm (Splittersnot applicable tobends under 45°)

Example with a minimumthroat radius (100 mm):

W Number ofsplitters

mmUp to 300 NoneOver 300 ,upt.05~ 1 .Over 500up to 1000 2Over 1000 3

Fig. 53 Medium radius(all ai1gles)

Fig. 54 Long radius(all angles)

Splitters should bepositioned so that the r{Wratio for each air passageis preferably above 1.5,with a minimum of 1.25.

Single skinvane

1/

'I

IarenDediate-1UJIPCIdI;endsaecwedto duct walla

DoUble ski,. ----,),ane

/.,/

/

----- -\,--pi... \.''-,

Table 12 Numberofturningvanes_, 0'-

r-SOmm

Minimum number ofWidth of duet turning vanes:

'W' double or single-skin

1 2

mm250 6300- '- f-- --'-- '9'400'---- .--~__~~____lLSQO ". .-.--

15_. --.- --..600 18800 24

Fig. 56 Twin radius-equal (all angles)·

--;;, /'\ "V

Fig. 57 Twin radius-unequal (all angles)·

Fig. 59 Branch(all angles)

•Splitters inaccordance with Figs.52(a) and (b)

BranchesFig. 60 90°branch

(rectangular orcircular)

....•••••••••c',•••••••.....•

Fig. 67 Concentric- j_.without splitters r~_.

Fig. 61 Angled branch(rect. or circ.)- allangles other than 90°

....,••••••••••cO,••••••••••....•

Fig. 68 Concentric- r·with splitters r~--

Branch duet Dimensionswidth (W) (A)

mm mm

Up to 200 75.. 300 100.. 400 125.. 600 ISOOver 600 200

.--•c'j"•~.-

....•••••;,•••••....•

Fig. 62 Shoe branch(rect. or circ.)

TransformationsFig. 70 Rect. to circ.-eccentric

Main duet Flat baropening backing

(longer side) straps

mmUp to 600 None

Over 600 up Internalto 1000 only

Over 1000 Internal andexternal

r:::: ••••.• [:2j, l...·~~•..... ---_ .....•

Fig. 71 Rectoto circ.- concentricFig. 63 Shoe branch

(rectangular) -high-pressure

:

..::: ~ '~-, l..··~{

•..... ----, ....•

•.......

t.... IS·max......

.....1Fig. 72 Cross-sectional

area retained

:;r•.•.....

•.....Jrt•..••• .....•

;,..•...1 . Fig. 73 Cross-sectional

area reduced

12 STANDARD SIZES12.1 '!\vo size ranges of circular ducts are in use inthe UK: ISO and Imperial. For design purposesthe same surface area, flow rate and frictionalresistance may be used for each correspondingsize.Col. 1 of Table 13 sets out the standard sizes accep-ted by the International Standards Organisationfor conversion into an ISO standard; and Col. 2gives the nearest Imperial size equivalent.

Nearest SurfaceISO standard Imperial area persizes (nominal size metre length

diameter (nominal (ISO sizesdiameter) only)

1 2 3

mm mm Sq. metres

63 64 0.19871 76 0.22380 - 0.25190 89 0.283

100 102 0.314112 - 0.352125 127 0.393140 133 0.440160 152 0.502180 178 0.566200 203 0.628224 229 0.704250 254 0.785280 279 0.880315 305 0.990355 356 1.115400 406 1.257450 457 1,413500 508 1.571560 559 1.760630 610 1.979710 711 2.229800 813 2.512900 914 2.826

1000 1016 3.1421120 1118 3.517125a 1270 3.927

Note. The above sizes are subject to the normal manu-facturing tol.w.ances.

13 CONSTRUCTION13.1 Spinlly.wound ductsThe minimum constructional requirements set outin Table 14 are common to the full range of pres-sures covered in this specification. The method offorming the duct and the specified cross jointsmake additional stiffening unnecessary.13.2 Straight«amed ductsTable 15 gives the differing minimum require-ments according to the pressure classification. Allstraight-seamed circular ducts shall be manu-factured with a swage not less than 40 mm or morethan 7S mm from each end, unless a reinforcingangle ring is fitted.If straight-seamed circular ducts are required to begalvanized after manufacture, the sheet thicknessused for such ducts shall be a minimum of 1.2 mm,irrespective of the size of the duct; and cross jointsshall in all cases be angle flanged.13.3 Lmagitudinal seams

13.3.1 Spirally·wound ductsThe grooved seam used in spirally-wound circu-lar ducts, provided it is tightly formed to pro-duce a rigid duct, is accepted as airtight to therequirements of all the pressure classificationscovered in this specification, without sealant inthe seam.13.3.2 Straight-seamed ductsThe longitudinal seam for straight-seamed cir-cular ducts shall be either the grooved seam(Fig. 74), continued to the extreme end of theduet and sealed during manufacture; or a con-tinuous butt or lap weld, provided this gives asmooth internal finish.

13.4 Cross joints13.4.1 GeneralCross joints for circular ducts, both spirally-wound and straight-seamed, are illustrated inFigs. 75 to 86. They include several proprietarytypes and the limits of use in terms of diameterand pressure classes are noted against each.13.4.2 Sealant/weldingSealant shall be used in all circular duct crossjoints, whether the ducts are spirally-wound orstraight-seamed. Alternatively, such crossjoints shall be continuously welded. (However,the synthetic rubber gaskets incorporated injoints Figs. 80 and 81 are regarded as providingan effective sealant for those joints.)The use of chemical-reaction tape or heat-shrinkable band shall be regarded as aneffective sealant in respect of the socket andspigot joints illustrated.

13.4.3 Socket and spigot joint without gasketWhere the joint is made with sealant, the endsto be joined shall either be carefully cleanedwith a suitable solvent to a length of 100mm andsealant applied to the spigot so as to give a jointlength in accordance with Table 18, or, sealantshall be applied in the alternative position indi-cated in figures nos. 75, 76, 77, 82, 83 and 84.Use of excessive sealant shall be avoided. Thejoint shall be held in place by a minimum ofthree permitted fastenings.

Where the joint is made by enclosure, such aswith a chemical-reaction tape, heat-shrinkableband or strap, or other approved material, themaker's instructions shall be followed.13.4.4 Flanged jointsThe duct end shall be turned up approximately10mm. Alternatively, the duct shall be continu-ously welded inside the angle flange. Sealant orgasket shall be used between the angle flanges.13.4.5 Welded jointsThe limitations for welded joints are given in13.5.5.

Maximum Minimum(nominal) sheet Minimum stiffening requirementsdiameter thickness

1 2 3

- mm mm

205 0.6 None

762 0.8 None

914 1.0 None

None if tube is also helically beaded.Iffacto~ made: Fi~. 75; if site made:

1020 1.0 Fig. 77 angle rein orced) or Fig. 78 or 79(angle flanged) - all at 3000 mm maximumspacing.

1525 1.2 Figs. 78 and 79 at 3000 mm maximum spacing.

Minimum sheet thicknessMaximum(nominal) Low-and High- Minimum stiffeningdiameter medium- requirements

pressure pressure

1 2: 3 4,

mm mm mm

205 0.6 0.8

-510 0.8 0.8 Swaged at both ends of all joints

762 0.8 1.0

1020 1.0 1.2 Swaged at both ends of all joints;30 x 3 mm angle rings at 1250 spacing

1525 1.2 1.2 40 x 4 mm angl~ rings at 1250 mm spacing

13.5 Fastenings13.5.1 Permitted types and maxmum centresTable 16 sets out the permitted fastenings andmaximum spacings for low-, medium- and high-pressure ducts. All duct penetrations shall besealed. .13.5.2 RivetsManufacturers' recommendations as .to use,size and drill size are to be followed. Rivetsresulting in an unsealed aperture shall not beused.13.5.3 Bolts and nutsBolts and nuts shall be of mild steel, protectedby electro-galvanizing, Sherardizing, cadmium-plating or other equal and approved finish.13.5.4 Self-tapping screwsSelf-tapping screws, while not recommended,are acceptable in circumstances in which the useof other types of fastening is not practicable.13.5.5 Welding ofsheetThe suitability of welding for sheet-ta-sheetfastening will be governed by the sheet thick-ness, the size and shape of the duct or fitting andthe need to ensure airtightness. Welded jointsshall provide a smooth internal surface and shallbe free from porosity. Distortion shall be keptto a minimum.Areas where the galvanizing has been damagedor destroyed by welding or brazing shall be suit-ably prepared and painted internally and exter-nally with zinc-rich or aluminium paint. -

14 FiTTINGS14.1 Standardisation oftittingsThe names and descriptions of circular duct fittingsas set out in Table 19 are recommended for adop-tion as standard practice, as being in the interestsof designers, quantity surveyors and ductwork

Table 16 Permitted fastenings andmaximum spacings-circular ducts

Sheet to section(cross joint flanges

Typeof Sheet to sheet and intermediatefastening (cross joints) stiffeningflanges)

Spirally- Straightwound seamed

1 2 3 4

mm mm

Mechanically 300 mm centres 150 150closed rivets (minimum three)

Bolts and nuts - - 300

Lock bol!S. - - 300Spot welds - - 150

contractors, and of those using computers in duct-work design and manufacture. .The requirements for circular duct fittings applythroughout the pressure. ranges covered in thisspecification.14.2 Nominal diametersThe nominal diameter (see Table 13) is the sizeused for design and ordering. With socket andspigot joints, care should be taken to ensure thatthe dimensions of the ducts and fittings are cor-rectly related, so that the joint can be effectivelysealed.14.3 Sheet thicknessSheet thicknesses for circular duct fittings (deter-mined by the largest diameter) shall be not lessthan those quoted in Table 17.14.4 Socket and spigot jointsThe minimum length of spigots are set out in Table18. Fittings larger than 510 mm diameter shall haveswaged ends.14.5 Sealing of jointsSealant shall be used in all cross joints of fittings.Such sealant shall be in accordance with the re-quirements of Section 27.

Table 17 Circular duct fittings-sheet thicknesses

. Maximum Minimum sheetnominal diameter thickness

1 2

mm mm

160 0.6

510 0.7

630 0.8

1020 1.0

1525 1.2

Maximum Minimum lengthduct diameter of spigot

1 2

mm mm

Fittings

160 30

315 40

1525 50

Closures 25

"41

Fig. 74 Grooved seam(straight-seamed ducts)

Circular duct cross joints

Limits of use

Angle Maximum Pressuresize diameter classes

mm mm

lww1020 MediumHigh

Fig. 75 Plain socket and spigot (duct to fitting)Fastening

~

\ \ Iww\ \ 1020 Medium\ \ High\ \\ ,\ ,\ ,\ ,, \\ ,,

\

..: : Altemati~e: :/ position for

: :: angle••_.•.•••.•.: •..•.•..••I

·Where angle rings specified

I I

*2Sx3*30x34Ox4

76210201525 ILow

MediumHigh -

Fastening

\" /:: ~ ~ ~:\ :: ~ :\ ::

Se~lant : : Sealant : :Turn up ::., :: or gasket: :minimum::\ II • I II

,,:: : :oflOmm::\:: • I ::

\ :: : : ::\ " I I ••---'-\~H- I I ...•.•.••1:---

Fig. 79 Angle flanged(internal)

Alternative sealant, locations

\\\\

JIISealantI or gasketI

III

Fig. 80 Socket and spigot with synthetic rubberdouble gasket

IIIII\1

Fig. 81 Socket and spigot with synthetic rUbbersingle gasket

\\\\\\\\\

Anglesize

(025 x3*30x34Ox4

*30x34Ox4

Maximumdiameter

76210201525

*Where flanged jointsare specified

10201525

Pressureclass

ILowMediumHigh

!LOWMediumHigh

*Where flanged jointsare specified

Not suit-able forhelicallybeadedspiraltube

Not suit-able forhelicallybeadedspiraltube

ILowMedium

ILowMedium

Fig. 82 Socket and spigot - ~Iain Alternative~~ sealant

~ locations

'\: FasteningIIIIIII

Fig. 83 Socket and spigot with connectorAlternativesealantlocations

;

Alternative~.sealant astenmglocations~ \

Fig. 85 Angleflanged

~Fastening : Gasket

IIIIIII---r--

l\I Turnup I

I minimum:I oflOmm II II II II I--+---

Limits of use

Angle Maximum Pressuresize diameter class

mm mm

800 l~wMediumHigh

*25x3*30x34Ox4

76210201525

ILowMediumHigh

ILowMediumHigh

*Only where angle ringspecified

*25x330x34Ox4

76210201525 ILow

MediumHigh

*Only where flanged jointspecified

Limits of useStraight-seamed duets Size of Maximum. Pressure

Oat diameter class

Fig. 86 Flatringflanpd

mm mm2Sx3 610 ILow3Ox3 1020 Medium

40xS 1525

Table 19 CIRCULAR DUCT FITTINGS-STANDARD NAME AND DESCRIPTIONS

Name and description Fig. No.

1 2

BendsSegmented - five section 900.. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 87Segmented - four section 60° .. .. .. .. .. .. .. .. .. .. .. .. .. .. 88Segmented - three section 45° .. .. .. .. .. .. .. .. .. .. .. .. .. .. 89Segmented - two section 300.. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 90Pressed - medium radius .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 91Pressed -long radius .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 92Pressed - tw,inradius (all angles) .. .. .. .. .. .. .. .. .. .. '. .. .. 93

BranchesSquare .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ·94Angles (all angles less than 90°) .. .. .. .. .. .. .. .. .. .. .. .. .. .. 95Conical .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 96Bell mouth .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 97Shoe .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 98Tangential .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 99Mitred .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 100

Change shapesConcentric taper .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 101Eccentric taper .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 102

TransformationsCircular to rectangular (concentric) .. .. .. .. .. .. .. .. .. .. .. .. .. 103Circular to rectangular (eccentric) .. .. .. .. .. .. .. .. .. .. .. .. .. 104

OffsetsMitred .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 105Radiussed .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 106

ConnectorsMale .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 107Female .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 108

ClosuresPlug end .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 109Cap end .. .. .. .. .. .. .. .. .. .. .. .•...... .. .. .. .. 110

Part Four - Fittings for circular ductsFor sealing requirements, see Sec. 14.5 (page 39)

Bends (segmented)

ITI

Fig. 87Segmented - five-section 90° (alsoacceptable as a

. four-segment bend)

Fig. 88Segmented - four-section 60°

Fig. 89Segmented-three-section ~5°

Fig. 90Segmented - two-section 30°

Note - All segmented bends shallhave a swage at each end.

Bends (radiussed)(~D or ID throat radius)

Fig. 91 Pressed- medium radius(available up to4OOmm)

Fig. 92 Pressed-long radius(available up to300mm)

Fig. 93 90° twinradius (made frompressed bendsFigs. 91 and 92)

Part Ft;Jur- Circular duet fittings - continued.

Branches (u.connection offdleduetorua separate fitting)

Fig. 94Square

Fig. 95Angled-allangles otherthan 90°

Fig. 96Conical

Fig. 97Bell mouth

Fig. 98Shoe

Fig. 99Tangential

Fig. 100Mitred

----'.,IIII,,i",,, ,

I ,I II II I,,_._-~,

Fir. 101 Taper-concentric

....,.,IIII,,

i", I, ,I ,I II II I,,_ .._~,

Fir. 102 Taper-eccentric

TransformationsFir. 103 Circular torectangular - concentric

·····1 ~J·····lh ~ __ .Fir. 104 Circular to

.rectangular - eccentric·····]_~· ...·l:h.... '---=- .....•

.....,I,A

"I ,, ,~_.. Fir. 105Mitred...~,,,,,,

, II I._.~

.....,I,A,,I ,I'~ ..-

Fir. 106Radiussed

._-~,I,,,,

, II ,.-.~

r· - - ---~- - - - - -:'.Fir. 107 \ ; ! [ )

, • I I'

Male /\ : : 'r'" I. •t , I I •

I , :: II,: :: .:~----- ------~

{-----_ ..•......· .· ., ,· ....•.._--_ ......•.

_··------n\... ...-------,

~

---)I I_._--

Fir. 110 ~- ---JCap end , I

___ .-l.'Fir. 109Plurend•

15.1 Table 20 sets out the standard sizes of spirally-wound oval ducts offered by the manufacturers of ducts ofthis section.

Nominal Surface Depth of duct (minor axis-'D')-nominalsheet area per

thickness metrelength 75 100 125 150 200 250 300 350 400 450 500

I 2 3

mm sq. metres mm mm mm mm mm mm mm mm mm mm mm

0.718 3200.798 360 350 330 3200.878 400 390 370 360

0.8 0.958 440 430 410 4001.037 E 480 470 450 440E

I 490 4801.117 -; 520 505c

1.197 ·s 545 530 5200cI.- .H

1.277 ~ 555 525I1.436 fIl 635 605 580.;(

CIS..1.596 0 715 690 660 630.;-E1.756 - 800 770 740 710 685 655U::I

1.915 "0 880 845 825 790 765 735 705 680'-0.c-0

2.075 ~ "0 960 930 900 875 845 815 785 755- ~2.238 CIS 1040 1010 985 955 925 895 865 835~

CI]

2.394 1120 1090 1065 1035 1005 975 945 9152.553 1200 1170 1145 1115 1085 1055 1025 1000

1.0 2.873 1335 1305 1275 1245 1215 1190 11603.192 146,1.1435 1405 1375 1350 13203.511 1625 1595 1570 1540 1510 14803.830 1785 1760 1730 1700 1670 1640

'1P

16 CONSTRUCTION16.1 General'Flat oval' is the term used to describe a duct ofcross-section with flat opposed sides and semi-circular ends. The duct is formed from a spiraiiy-wound circular duct, using a special former.

Apart from stiffening (for which see Tables 21 and22), flat oval ducts have the same constructionalrequirements throughout the pressure rangescovered in this specification.Flat oval ducts may also be formed from flat sheetwith straight seams (see Section 17).

Table 21 - Flat oval ducts - low- and medium-pressure - stitTening requirements

Tie rodsDepth of duct (minor axis-'D') - nominal

75 100 125 150 200 250 300 350 400 450 5001 2

mm mm mm mm mm mm mm mm mm mm mm

320360 350 330 320

Not required 400 390 370 360440 430 410 400480 470 450 440ee 520 505 490I 480

co= 545 530 520"s0= 555 525I-~ 635 605 580

Fig. III I 715on100 mm centres "=ClJJ) •.. 8000"(i'

e 880 680-1:$Fig. 112 ='"0 960 755-750 mm centres 0m -= 1040 835-"0

~1= 1= I . 1120 915

Fig. 113 1200500 mm centres

et[1J) 1335 1305 1275 1245 1215 1190 1160I II I 1435I I 146j 1405 1375 1350 1329\•••• , = 1= I

1625 1595 1570 1540 1510 1480

1785 1760 1730 1700 1670 1640

Table 22 - Flat oval ducts - high-pressure - stiffening requirements---_ ..- --_ ..__ .

Tie rodsDepth of duct (minor axis-'D') - nominal

75 100 125 150 200 250 300 350 400 450 SOO

1 2

mm mm mm mm mm mm mm mm mm mm mm

320

360 350 330 320400 390 370 360

440 430 410 400

Not required 480 470 450 440

520 505 490 480

e 545 530 520eFig. 114 I 555 5251000 mm centres -;

(~c·s 635 605 5800c

Fig. liS I 715750 mm centres ,....

etlJ) ~ 800I

~ on 880 680'>:e(0

""Fig. 116 0 960 755.•...(0500 mm centres e- 1040 835-uet:tI:D ='I I "0

• I ... 1120 915I 01-1- I -I .c-"0 1200 1000

~Fig. 117 1335 1305 1275 ·1245 1215 1190 1160

ett11J) 1465 1435 1405 1350 1320!;t--~r 1625 1595 1570 1540 1510 1480E 1_ -f- - -1-1-1-,-1~I - :SectlOll AA A1l+-+.J A 1785 1760 11730 1700 1670 1640

~ ::J

16.2 Longitudinal seamsSpirally-wound flat oval duct is accepted as airtightto the requirements of this specification withoutsealant in the seams, provided the grooved seam istightly formed to produce a rigid duct.16.3 Cross jointsCross joints shall be as Figs. 75, 76 or 77, or suchother joint as can be shown to the designer to beequally satisfactory.Sealant, whether mastic, chemical-reaction tapeor heat-shrinkable tape) shall be used in all crossjoints.

16.3.1 Socket and spigot jointsWhere the joint is made with sealant. the endsto be joined shall be carefully cleaned with asuitable solvent to a length of 100 mm and seal-ant applied to the spigot so as to give a jointlength as for the requirements for circular ducts- see Table 18. Use of excessive sealant shall beavoided. The joint shall be fixed with permittedfastenings at 60 mm centres. on the flat surfacesonly.Where the joint is made by enclosure. such aswith a chemical reaction tape. heat shrinkableband or strip, or other approved material, themaker's recommendations shall be followed.Care should be taken to maintain close contactbetween the material and the flat sides of theduct until the joint is completed.16.3.2 Flanged jointsWhere conditions require the use of flangedjoints, they shall be as Fig. 78 or 79. Alterna-tively, the duct shall be continuously weldedinside the angle flange. Sealant shall be usedbetween the duct and the spigot, and sealant orgasket between the angle flanges. The flangedjoint shall be secured by bolts and nuts at 150mmcentr~s.

16.4StiffeningThe larger sizes of flat oval duct are stiffened byswages. as indicated in Table 20. Additionally, tierods (see Figs. 118 to 120) are required. positionedas indicated in the respective tables and illustrations.As an alternative to tie rods, stiffening in the formof external angles may be used to meet the require-ments of the corresponding rectangular duct sizes.

17 CONSTRUCTION (STRAIGHT-SEAMED)17.1 Flat oval ducts with opposed sides andsemi-circular enas may also be formed usingplain sheet and straight seams. Ducts so formedshould follow the metal thicknesses and stif-fening requirements specified for the corres-ponding sizes of rectangular ducts, except thatstiffening is necessary on the flat sides only.Seams and cross joints shall be sealed to ensurethe necessary degree of airtightness throughoutthe pressure ranges covered in this specification.

18 FITTINGS18.1General constructional requirementsSheet thicknesses for flat oval fittings (determinedby the periphery of the larger end) shall be not lessthan those given in Table 20 for the ducts them-selves.With socket and spigot joints, care should be takento ensure that the dimensions of ducts and fittingsare correctly related.All the seams and joints integral to a fitting shall besealed to the same standard as the duct.18.2 Standard Ottings for flat oval ductsTable 23 lists the basic forms and accepted namesfor the flat oval duct fittings; typical illustrationsare given in Figs. 121to 136. The basic forms, usedin combination, will cover the full range of fittingsfor flat oval ducts.

Fig. 118 With internal andexternal nuts

Table 23 FLAT OVAL DUCT FITIINGS-STANDARD NAMES AND DESCRIPTIONS

Name and description Fig. No.

Bends

Segmented - five-section goo (hard) ... .. ., .. .. .. .. .. .. .. .. .. 121Segmented - five-section goo (easy) .. .. .. .. .. .. .. .. .. .. .. .. 122Segmented - three-section 45° (hard) .. .. .. .. .. .. .. .. .. .. .. 123Segmented - three-section 45° (easy) .. .. .. .. .. .. .. .. .. .. .. 124Square (hard) (rectangular body, flat oval ends) .. .. .. .. .. .. .. .. 125

,

Square (easy) (rectangular body, flat oval ends) .. .. .. .. .. " .. .. 126Square (hard) .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ... 127Square (easy) .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 128Twin .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 129

Branches

For fitti~s off flat proIDe, see rectangularfittings, igs. 60, 61 and 62For branches off semJ-clrcular profile, see circularfittings, Figs. 94 to 100

Tapers

Reducer - concentric .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 130Reducer - eccentric .. .. .. .. ., .. .. .. .. .. .. .. .. .. .. 131

Transformations

Flat oval to circular .. .. .. .. .. .. .. .. .. .. .. .. .. " .. .. 132Flat oval to rectangular .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 133

Offset

Mitred (hard or easy) .. .. .. .. .. .. .. ,. .. .. .. .. " .. .. 134

Coupling .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 135Closure - 136.. .. " .. .. .. .. .. .. .. .. .. .. .. ., " .. ..

••

Part Five - Fittings for flat oval ductsFor sealing requirements, see Sec. 18.1 (page 50)

Bends Ie Bends (ctd)Fig. 121 Fig. 129Segmented- Twinfive-section90° (hard) -1 o.f.-

Fig. 122 I-W-lSegmented-T CDfive-section 0 Tapers90° (easy) _t_

Fig. 130 --I D r-Reducer- ~II8concentric

18Fig. 123 fBw,Segmented-Fig. 131 B- a.three-sectionReducer-45° (hard)eccentric-jol--

!-W-j TransformationsFig. 124 t; .,- en Fig. 132 gSegmented-

_./. \,~ 0 Flat oval to {"three-section _t_ circular I,'.

"45° (-:asy) 1 I.•..

Fig. 125 T 8 Fig. 133 [QJSquare (hard) w Flat oval to(rect. body. 1 rectangularflat oval ends)

!--W....-.1 -j0r-OffsetFig. 134Mitred

Fig. 126

~

T OJ (hard or easy)Square (easy) 0

-L(rect. body. I-w-iflat oval ends) f40.-.j

Fig. 127 -t 8 Co~pling

trSquare W Fig. 135

~

T(hard) _! w

-1of- 1I-w-!Closure

.,..Fig. 128

~

T CD Fig. 136

~

Square (easy) 0-L r-w-t

I-D-j

Part Six - Hangers and Supports

19 GENERAL19.1 Principles adoptedSupports are an essential part of the ductworksystem, and their supply and installation are nor-mally the responsibility of the ductwork con-tractor. The choice between the available methodsof fixing will depend on the type of building struc-ture and on any limitations imposed by the struc-tural design. Further, unless the designer hasspecified his requirements in detail, the load to becarried shall be understood to be limited to theductwork and its associated insulation.It is not practicable to deal here with the full rangeof supports available, which increasingly includesproprietary types, so in this section variousmethods of support are dealt with in principleunder the three elements of:(1) the attachment to the structure;(2) the hanger itself; and(3) the duct support;with illustrations of those most commonly used.Speciat"attention has been given to the treatmentof supports for insulated ducts, with and withoutvapour sealing.Supports for ductwork external to the buildinghave been excluded, as these are individually de-signed to suit the circumstances, and also may berequired to meet local authority standards. For thesame reasons, floor supports have not been dealtwith.With a proprietary device, it will, unless thedesigner has specified his requirements in detail,be the responsibility of the ductwork installer toensure that it meets requirements, with a sufficientmargin of overload; and that it is installed in accor-dance with the manufacturer's recommendations.The absence of any method or device from thisspecification does not preclude its use if it can bedemonstrated that it is suitable for the duty assign-ed to it, with a sufficient margin of safety againstoverload; and this will be the responsibility of theductwork installer, unless the designer has .speci-fied his requirements in detail.19.2 Fixing to building structureThe fIXingto the building structure should be of astrength and durability compatible with those ofthe ductwork support attached to it. A fIXing toconcrete or brickwork must be made in such a waythat it cannot loosen or pull out through normalstressing or through normal changes in the build-ing structure.

19.3 Horizontal ductwork19.3.1 Attachment to structureAttachments may be secured to the structure bymeans of an expansion anchor (Fig. 137) orchannel section (Fig. 138). The use of the shot-fired type of bolt in a vertical position is notrecommended as a support for a suspended load.Where duets are supported from walls, thebearing member is normally built into or at-tached to the wall and the duct suspended orsupported therefrom.Attachment to the building frame may be madeby means of beam clamps (Fig. 139) or springclips or books (Figs. 140). In addition, springclips adjustable for height (Fig. 141)can be usedwith rod or studding.While application and loading are the main fac-tors in the choice of attachment, the conse-quences of dislodgement should be consideredif those relying merely on friction, e.g. springclips, are used.19.3.2 The hanger itselfThe hanger itself is usually mild steel plain rodor studding or Oat strap, pre-treated by, e.g.hot-dip galvanizing, Sherardizing, electro-deposited zinc plating or by some other accept-ed anti-corrosion treatment. Other materials,such as stranded wire, may also be acceptable.Projection of a rod or studding hanger throughthe bottom bearer should, where practicable,not exceed twice the thickness of the securingnut.Provided the integrity of the ductwork is main-tained, hangers may be attached to the comersof the flanges as an alternative to the use of abottom bearer.With proprietary devices manufacturers'recommendations for use should be followed.19.3.3 The duct supportThe choice of the lower support will be dictatedby the actual duct section.19.3.3.1 Rectangular ductsTable 24 gives minimum dimensions for thehangers and for angle, channel and profile sec-tions. The angle is shown in Fig. 142, the chan-nel in Fig. 143 a~ the profile sections in Figs.144and 145.Typical arrangements of bottom bearer sup-ports for plain, insulated and vapour-sealedducts are shown in Figs. 146 and 147. Alterna-tive methods of support for such ducts, using

comer cleats, are shown in Figs. 148, and usingstirruP. brackets in Figs. 149 and 150.19.3.3.2 Circular ductsTable 25 gives minimum dimensions for thehanger and for the brackets. The three commonmethods of supporting circular ducts are: thestrap hanger (Figs. 151 and 153 - limited toducts with a diameter not exceeding 300 mm;the half band clip (Figs. 155 and 157); and thesplit band clip (Figs. 152and 154).19.3.3.3 Flat oval ductsTable 26 gives the mininum dimensions for thehanger; and for the bearer, depending onwhether the flat side of the duct is horizontal orvertical.Typical arrangements for flat oval duct supportsare shown in Figs. 156and 158.

19.4 Vertical ductsThe design of supports for vertical ducts is dictatedby site conditions, and they are often located tocoincide with the individual floor slabs, subject toa maxim~m spacing of 4 metres.Vertical ducts should be supported from the stif-fening angle or the angle frame, or by separatesupporting angles fixed to the duct.A typical method of supporting vertical rectangu-lar ducts is shown in Fig. 159 and for circular ductsin Fig. 160. The same methods are applicable tovertical flat oval ducts.

19.5 Heavy loadingsFor ducts "larger than those covered by Tables 24 to26, or where heavy equipment, mechanical ser-vices, ceilings or other additional load is to beapplied to the ductwork, supports shall be design-ed to suit the conditions.19.6 Insulated ductsWhere ductwork is required to be insulated, thismust be clearly specified, so that hangers arespaced to provide clearance for the insulation.Otherwise, supports may be as for uninsulated

ductwork. Where fire regulations apply, approvalof the relevant authority may be needed.

19.6.1 Insulated ducts with vapour sealingWhere the temperature of the air within theduct is at any time low enough to promote mois-ture penetration through the lagging and causecondensation on the exterior surface of theduct, vapour sealing may be called for, and inthis case the most important requirement is tolimit penetration of the seal.The extent of any vapour sealing of ductwork,and the method to be used, must be clearly speci-fied in advance, as follows:Method 1Where the risk of damage due to condensationis slight, the vapour seal can be applied to theinsulated duct and made good round the sup-ports to achieve an acceptable level of proofing.Method 2Where it is essential to keep penetration of thevapour seal to a minimum, supports should beexternal to the insulation, as shown in Figs. 147,150, 154, 156, 157 and 158.The insulation and vapour barrier should beabutted to the insulator incorporated with theduct support. This' insulator shall be non-hygroscopic and shall be capable of carrying theimposed load without significant compression.Typical materials are hardwood or treated soft-wood (in separate block form for circularducts); GRP (glass-reinforced plastics); andhard rubber compounds. Some proprietarysystems of support for vapour-sealed ducts areavailable.19.6.2 Heat transferIt is not normally necessary to make specialarrangements for the limitation of heat transfervia the duct supports. However, there may bespecial cases where the temperature differencejustifies a heat barrier to conserve heat or toprevent condensation.

Hanger Bearing memberMaximum Maximumduct size Rod or Rolled steel Rolled steel Roll formed spacing

(longerstudding Flat strap an~e channel channel of

~:;a:~ (two) (or at) section section profile hangerside) W WHnu Hnu

1 2 3 4 5 6 7

mm mm mm mm mm mm mm

H W H W H W400 6 25 xO.8 25 x25 x 1.5 25x25x 1.5 20x25 x 1.5 3000

(plain or (or 25 x 3 flat)perforated) (plain)

25x3600 8 (plain) 25x25x3 25x25x3 25 x25x 1.5 3000

30x31000 8 (plain) 30x30x3 25x30x3 . 30x25 x 1.5 2500.

40x51500 10 (plain) 4Ox40x3 30x40x3 4Ox25x 1.5 2500

4Ox52000 10 (plain) 4Ox40x4 30x40x4 4OxZ5 x 1.5 2500

4Ox6According to circumstances3000 12 (plain)

Hanger Bearer Maximum spacingMaximum Drop rod

duct or studding Flat strap Stirru~ Wrap-round Spirally- Straight-or split wound seameddiameter ~two~ (two) (Fig. 1 5) clip duct ductdia.

1 2 3 4 5 6 7mm mm mm mm mm mm mm305 - 25 xO.8 - 25xO.8 3000 1800

(plain or (plain orperforated perforated)

--Sf,; 8 25 x3 30x4 25x3 3500 2500(plain)

1016 10 40x5 40x5 - 3500 2500(plain)

1524 10 4Ox5 40i5 - 3500 2500(plain)

Notes to Tables 24 to 26(1) The dimensions included in Tables 24 to 26 are"

to be regarded as minima.(2) The maximum spacings set out in the tables

are related solely to duct weight consider-ations. Closer spacings may be required byreason of the limitations of the building struc-ture or to achieve the necessary duct rigidity.

Table 26 Supports for horizontal ducts - Oat oval

Maximum Hanger Bearerlength

Drop rod Flat Flat Rolled Maximumof or studding strap strap steel spacingmajor

~:a~~(two) Fig.1S4} angle

axis

1 2 3 4 5 6

mm mm mm mm mm mm

400 8 2SxO.8 2Sx3 2Sx2Sx3 3000(plain or (plain)

perlorated)

60S 8 2S x3 30x4 2Sx2Sx3 3000(plain) (plain)

1005 10 30x3 40xS 30x30x3 3000(plain) (plain)

1510 10 40xS - 4Ox40x3 3000(plain)

-m

(b) With flatstraphanger

Fli. 141 SlldlnlIprinldip

Fig. 142Rolled steelangle

Fig. 143Rolled steelchannel

, Ar-, J ~ V r-,I I II I II I I II I II I I II I II I I II I I I

~~------------- ,~--------------~Fig. 146 Rectangularduet-plain or Insulated. Can bevapour sealed to Method I.Also applicable to flatoval duets.,f---l~

"I}II!,\1,',

: \\ I~ .~.\. ,. .IFig. 148 Rectangular duet with

comer brackets - plain orInsulated. Can be vapoursealed to Method I.

bFJFl•• 144Profilechannel(alternatives)

FII. 145 Inverted profilechannel (alternatives)

.Fli. 147 Rectangular duct-Insulated and vapour sealedtDMethod2.

IIIIL _

FII. 149 Rectangular duet withstirrup bracket - plain orInsulated. Can be vapoursealed tD Method I.

4Fl.. ISO Rectangular duct with

stirrup bracket. Insulated andvapour sealed tD Method 2.

Part Six - General- Hangers and Supports - continued.

Not to be usedon duetslargerthan300mmdiameter

Fig. 151 Circular duct withwrap-round strip hanger - plainor Insulated. Can be vapoursealed to Method I.

Fig. 152 Circular duct withipllt clip bracket - plain orInsulated. Can be vapour sealedto Method I.

Fig. 154 Circular Insulated duct with split clipbracket. Vapour sealed to Method 2.

Applies to bothFigs. 156 and 157

Insulatingspacer/'

Insulation'\

Not to be usedon duets largerthan 300mmdiameter

Fig. 153 Circular duct withstrip double hanger - plain orinsulated. Can be vapour sealedto Method I. (Applicable also toflat oval ducts)

Fig. 155 Circular duct withstirrup bracket - plain or insulated.Can be vapour sealed to Method I.(Applicable also to flat oval ducts)

Sheetmetal ---Fig. 156 Flat oval strip

., Flat oval or circular insulated duet with stinup bracket.Vapour sealed to Method 2. For ftat oval insulated duet' .•pour sealed 10 Method 1. see fill. 146. Insulation

\

Insulatingspacer-

Bea~rFig. 158 Flat oval Insulated duct with IIOttom bearer.

Vapour sealed to Method 2.

""- Sheet metalstrip

~ ...' i••,. • II' I I

I I. II II II

,I ,• I

0 0 0 0

Plain or insulated. Can be vapour-sealed toMethod 1.Vapour-sealing to Method 2 is notapplicable with vertical duet supports.

I'... , .i: R.S. flatforangle

Plain or insulated. Can be vapour-sealed toMethod 1. Vapour-sealing to Method 2 is notapplicable with vertical duet supports.

20 ALUMINIUM DUCTWORK20.1 ScopeThis section applies only to aluminium ductworkoperating at low pressure, as defined in Table 1.In general, the requirements of this specificationfor low-pressure galvanized steel ductwork alsoapply to aluminium ductwork, subject to the spe-cial provisions set out below.20.2 MaterialsThe aluminium sheet used should be chosen fromthose mentioned in Appendix J.20.3 Construction - rectangular ductsTable 27 sets out the minimum constructional andstiffening requirements for rectangular aluminiumducts and the permitted types of cross joint.

20.4 SealantThe sealant requirements set out in this specifi-cation for galvanized steel rectangular ductworkalso apply to the longitudinal seams and crossjoints in aluminium ductwork.20.5 Construction - circular ductsTable 28 sets out the minimum constructional and

stiffening requirements for circular ducts madefrom aluminium, and the permitted types of crossjoint.20.6 Fastenings

20.6.1 The types of fastening and the maximumspacings specified in Table 10 (rectangular) andTable 16 (circular) apply to aluminium duct-work, except that such fastenings shall be ofaluminium, stainless steel or monel metal.19.6.2 Some notes on the welding of aluminiumare contained in Appendix J.

20.7 Finishes20.7.1 No protective finishes are required foraluminium ductwork used indoors or outdoorsin normal atmospheric conditions. Appendix Jgives information on the use of protective fin-ishes for aluminium where it is considerednecessary for their application.20.7.2 Mild steel section used with aluminiumductwork shall be protected as specified in Sec-tion 28 (Table 30).

~Rectangular aluminium ducts - constructional requirements

Maximum sfsacing MinimumMaximum Minimum Suitable between joints stiffeners aluminiumduct size sheet cross-joints With cross angle section

(longer side) thickness Plain breaking or for cross-jointssheet pleating and stiffeners

1 2 3 4 5 6mm mm Figs mm mm mm400 0.8 9,10,33 - - -600 0.8 11,12,33 1500 - 2Sx25x3800 1.0 11,12,33 1200 1500 30x30x4

1000 1.0 11,12,33 800 1200 4Ox40x41500 1.2 11,12,33 600 800 4Ox40x42250 1.2 33 600 800 50x50x53000 1.6 33 600 600 6Ox60x5

Table 28 Circular aluminium ducts (spirally-wound and straight-seamed) -constructional requirements

Spiral-wound duct Straight-seamed duct Minimum anglesection for cross joints

Normal Minimum· Normal Cross Minimum and stiffenersCross

sheet joints stiffening sheet joints stiffening Ductthickness requirements thickness requirements diameter angle

mm mmas for figs as for as for figs as for· 510 25x25x3

galvanised 75 - 81 galvanised galvanised 82 - 86 galvanised 1020 30x30x4duct withLP duct duct withLP ductTable Limits Table Table 15 limits Table 1525 50x50x5

14 14 Co!. 2 15

21 ACCESS OPENINGS21.1 GeneralAll access openings shall be rigidly framed, withairtight covers designed so that they can be speed-ily removed and refixed. Multiple set screws arenot recommended, and self-tapping screws are notacceptable, as a method of fixing.

21.2 Access and inspection covers2-1.2.1 Subject to the restrictions imposed byduct dimensions, openings for access should notbe smaller than 375 x 300 mm or larger than 45Q..x 375 mm.i andopenings for inspection shouldhave a minimum diameter of 100mm.21.2.2 It shall be standard practice to provideaccess covers for the inspection and servicing ofplant and equipment as follows.

21.2.2.1 Fire dampersCover to be so located as to give access bothto the damper and fusible links.21.2.2.2 Control dampersCover to be so located as to give access toblades and linkages on ducts with diameteror side larger than 400 mm. In branch ductssmaller than 400 mm diameter or side,inspection openings for dampers, not smallerthan 100 mm by 100 mm, shall be used, withairtight cover as 21.1. .21.2.2.3 FiltersCover to be located upstream. (Note:Dimensions of access openings may need tobe changed to suit filter elements of the frontwithdrawal type.)21.2.2.4 Cooling coils, beater batteries andhumidifiersCover to be located upstream.

21.3 Hinged access doorsIt shall be the designer's responsibility to indicateon the drawings the location of any hinged accessdoors required. Unless otherwise specified by the

designer, openings sbould not be larger tban 1350mm high by 500 mm wide. Doors shall openagainst the· air pressure. Both the opening in theduct and the access door itself should be adequate-ly reinforced to prevent distortion. A suitable seal-ing gasket shall be provided, together with suffi-cient clamping type latches to ensure an airtightand watertight seal between the door and the duct. ,The latches shall have handles which can be oper-ated from both the inside and the outside of thedoor..For safety reasons, the designer should incorporate ftmeans to prevent personnel being trapped inside l\the duct, e.g. with operating handles both insideand outside the duct.

21.4 Test holes for plant system commissioningIt shall be standard practice to provide test holes,normally 13 mm diameter and fitted with an effec-tive removable seal, at the following locations: atfans (in the straightest section of duct near to thefan outlet); at cooling coils and heater batteries(both before and after tbe coil or battery). Thelocation of these holes shall be confirmed by thedesigner.Cl.S Access openings in insulated ductsWhere ducts are to be thermally insulated, it isrecommended that the frame of the access door orcover be extended beyond the face of the duct by ameasurement equal to the thickness of the insula-tion and be so arranged that the insulation andfinish can be 'dressed' into the frame, therebyensuring that the opening is not concealed and thatthe edges of the insulation are protected from acci-dental damage. If it is necessary to insulate theaccess door or cover, it should be dished to containthe insulation.

21.6 Hand holesHand hol~s to permit proper joining of duct sec-tions shall be provided at the manufacturer's dis-

cretion, but should be kept to a minimum andmade as small as practicable. They shall be render-ed airtight with sealant and securely 'fastened.21.7 Instnunent connectionsInstrument connections shall be provided where

22 CONTROL DAMPERS22.1 FunctionControl dampers used in ductwork have threefunctions:

22.1.1 IsolationTo act as a shut off.· Normally, the damper willbe fully open, or fully closed. In the fully-openposition, the damper should have minimumresistance to air flow, and when closed,maximum shut off. This type of damper is eitherhand- or power-actuated.22.1. 2 BalancingTo achieve the required distribution of air in theductwork system or at inlets and o\Jtlets. Forthis purpose, the damper is fixed manually inany required position between fully open andfully closed.22.1.3 ControlTo-secure dynamic control of the air flow in theductwork system. In this function, the damperwill always be power-actuated and may requireto be continuously or intermittently operatedfrom fully open to fully closed, and to becapable of taking up any position between theseextremes. In the fully-open position, thedamper should have a significant pressure drop.In the fully-closed position, it will not neces-sarily achieve a complete shut-off.

22.2 Types of control damperControl dampers of various types are available forspecific purposes, as follows.

22.2.1. Single-blade dampers single skin sectionPlain-blade dampers (single-skin section) shallhave a maximum width of 300 mm and maxi-mum length of 300 mm for rectangular duct~and for circular ducts a maximum diameter of305mm.22.2.2 Single-blade dampers double·skin section.Plain-blade dampers (double-skin section) are.suitable for use in rectangular ducts, and shallhave a maximum width of 300 mm and a maxi-mum length of 1200mm.22.2.3 Multi-leaf dampers (single or doubleskin) parallel and opposed bladeThere is no restriction on the size of duct inwhich multi-blade dampers may be used, but noindividual damper blade should exceed 1200mm in length or 175 mm in width. Where

shown on the contract drawings, suitably drilled or. bossed and screwed to sizes Jiven. .21.8 Openings required for other purposesIt shall be the designer's responsibility to specifythe location .and size of any openings requiredother than those covered in 21.2 and 21.4.

dampers are required for spans in excess of 1200mm, the frames should be sub-divided or inter-mediate bearings used.22.2.4 Iris dampersIris dampers are available (for circular ductsonly) in diameters up to 460 IDDl. (It should beremembered that the damper casing is approx-imately twice the diameter of the duct.)

22.3 Constructional requinments22.3.1 Low- and mediam-pressure integraldampersThe following recommendations apply todampers forming an integral part of low- andmedium-pressure ductwork.The dampers shall be constructed to preventdistortion and jamming in operation. Damperblades shall be without sharp edges. The bladesshall be sufficiently rigid to eliminate movementwhen locked.The blades shall be securely bolted to platedsteel spindles, the ends of wmch shall be ex-tended to the outside of the duct, with a groovein line with the blade. Spindles shall be carriedin non-ferrous or nylon plain bearings or in ballbearings. All control dampers shall have a lock-ing device located on the outside of the duct andshall give clear indicati.oo of the actual damperposition.22.3.2 Control dampers In high-pressuresysteinsControl dampers will not normally be posi-tioned in high-pressure ducts: essential dampersshould be confined to areas of relatively lowpressure.Control dampers used in high-pressure ductsshall meet the constructional requirementsspecified in 22.3.1, shall preferably have ex-temallinkages, and aUpenetrations of the ductshall be fitted with suitable seals.22.3.3 Proprietary types of control damperProprietary control dampers. are .commonlyseparate units rather than integral parts of theductwork. The use of any specific type of con-trol damper shall be confirmed with thedesigner. In all cases, proprietary dampers shallmeet the relevant requirements of thisspecification.

23 FIRE DAMPERS23.1 GeneralFire dampers are required in air distributionsystems for fire' and smoke containment.Generally they are called for where ducts pene-trate walls or floors which form fire barriers. Thedamper assembly, when built in, should have a fireresistance rating equal to that of the fire barrier itpenetrates.The construction and location of fire dampers arefor the designer to specify to meet the require-ments of the authority directly concerned with theinstallation.23.2 TypesThe main types of damper are single-plate, multi-leaf and shutter. Fire dampers of these types areillustrated diagrammatically in Figs. 161to 164.

Hinged dampers should where possible close in thedirection of the air flow.Where high velocities are involved, damper bladeswhen in the open position should be clear of the airstream; therefore the arrangements shoWnin Figs.161and 163are not recommended.Multi-leaf dampers are not recommended for usein vertical ducts but shutter dampers may be usedwith the addition of an actuating spring.

23.3 ConstructionIn the absence of a generally agreed standard forfire dampers, the detailed construction cannot bespecified. However, BS 476, Part 8, covers currentrequirements for· fire resistance of building con-struction. Proprietary dampers are in general useand it will be the damper manufacturer's responsi-bility to meet the specification for construction andoperation.

23.4 Corrosion resistanceIt is recommended that fire dampers be made froman inherently corrosion-resistant material orotherwise protected to inhibit corrosion. (Somefire authorities make this a requirement).23.5 Fusible deviceEach fire damper blade assembly shall be held inthe open position by a fusible devic8Jl(normallyspecified by the fire authority to release at a temper-ature of 72°C), and must be designed to ensurerapid closure on release of the link.23.6 AirtightnessFire damper casings shall be constructed to thestandards of airtightness applying to the system ofwhich they form part.23.7 LocationThe effective formed barrier of the fire damperassembly shall be located within the structuralopening. Where this is not possible the section ofthe casing outside the fire barrier must have a fireresistance not less than that of the fire barrier andbe adequately protected against the posssibility ofdamage by impact.

23.8 Provision for expansionFire damper assemblies generally include built-inclearan~ frames to meet the requirement that thecasing be free to expand in the event of fire. Theintegrity of the fire barrier is maintained either bymetal to metal contact or by fire resistant packing.Acceptable arrangements are shown in Figs. 165and 166.

Fire dampers

.-----_ ...-

., I-I" ,.: "\ ,,':I ••• ' t, ',,' I, ,.. II , '" I

: I" '\ •• :~:_-•...._.:~Hinge

Stop"

r .Damper blade Fusible link :•••• /!

: ',,' :I • I-..-- : " \, :

Air flow i,," \\1•..__ _.

~_._-----I", ' I: '.. "1: x" iI ,,, II ' •••• I

I " " :"-' :.1

Damper blade~

Fusible link

Fig. 165 Standard approved ~ethod offraming applicable to Fig. 164

This design wasdevelopedin collaboration byHVCAand the HEVAC Associationand is approved by theGreater London Council

Split frameassembledaround damperand built intofire barrier

24 BENDABLE AND FLEXIBLE DUCTS -METALThere' are two types of these ducts: (a) metal(including plastics-coated metal), which can bebent but not repeatedly flexed; and (b) ducts inmetal, which can be flexed a limited number of timeswithout failure.Ducts of these types may require special consider-ation in relation to fire hazards, and it is thereforeadvisable that the requirements of the relevant fireauthority are met before installation.24.1 Types available

24.1.1 Bendable ducts - metalA number of bendable ducts are available,helically-wound with lock seam to form a corru-gated duct capable of being bent or set by handwithout spring back and without deforming thecircular section. The metals used are 1fI\uni-nium. stainless steel, tin-coated steel oraluminium-coated steel. Plastics-coated bend-able ducts are also available.24.1.2 Flexible ducts - metalSome proprietary ducts of this type, in variousmetals. are available, having single or multiplelayers of strip formed into corrugations andwound in helical or annular form, without anyobvious seam or joint.

24.2 PerformanceBendable and flexible ductwork must meet thes~andards of airtightness requ~red by the specifica-tion and be within the frictional limits specified bythe designer.

Fig. 166 Framing applicable tDFigs. 161,162and 163

This method isalso normallyused for amultiple assemblyof shutter-type firedampers

Expansion spacefilled withcompressiblefire resistantpacking

\ Angle framessecured afterfire barrieris built

24.3 Manipulation24.3.1 ~neralBendable or flexible ducts made of aluminium(particulariy hi the bu-ger diameters) can bebent and manipulated more readily' than thosemade of steel, but are more easily distorted andmore susceptible to damage.Because of the spiral corrugation and lockseam, care is necessary when cutting.24.3.2 Bendable ducts - metalBends are made by closing the corrugations inthe throat and slightly opening the corrugationsat the back of the bend. Some readjustment ispossible with large radius bends, but smallradius bends cannot be straightened withoutleaving some distortion of the corrugations.Repeated bending should be avoided. Caremust be taken to maintain the integrity of thelock seam.Elongation and compression are limited, andthis must be taken into account with short con-

. nections between fixed points.24.3.3 Flexible ducts - metalThese ducts will withstand several bendingsthrough 1800 and will accept' sufficient linearcompression and re-expansion to facilitateinstallation between oppositely located spigots.

24.4 JointingJoints can be made with sealant or by enclosureusing heat-shrinkable band or strip or by chemical

re~ction tape.When sealant is used, it should form a continuousbarrier, and this can be achieved by a build-up ofsealant against the swage on the spigot or by anequivalent stop.Whichever method of jointing is chosen, it shouldensure that the air passage resulting from the spiralcorrugation is sealed.Fastenings should be as for rigid circular ducts(Table 16).

24.5 SupportsThe light weight of the duct, plain or pre-insulated,makes heavy and closely-spaced supports unneces-sary. If in doubt, the manufacturer's recommen-dations should be followed.

25 FLEXIBLE DUCTS - FABRIC25.1 Function

.The principal use of non-metallic duct is to joinrigid ductwork to terminals in cases where a flex-ible duct is needed to make a short connectionbetween fixed points.As these types of duct may constitute a fire hazard,it is essential that the requirements of the relevantfire authority are met in all cases.25.2 ConstructionSuitable constructions available comprise: (a) atough, tear-resistant. fabric liner and cover,proofed with synthetic rubber, enclosing a gal-vanized spring wire helix and reinforced with anouter helix of glass-fibre cord. This type of duct isalso available without a liner.(b) A tough, flexible aluminium laminate, sup-ported by a reinforcing helix of aluminium alloy orsteel.Other constructions for flexible ducts are avail-able, but in all cases they should comply with therequirements of25.3.

26 FLEXIBLE JOINTS26.1 General propertiesThe material (normally a treated canvas) used forflexible joints must meet any conditions of tem-perature, air pressure and fire resistance specified,and shall comply with the standard of airtightnessspecified for the rest of the ductwork syste~ ofwhich it forms part.26.2 LocationFleXIble joints should normally be fitted at inletand outlet connections to all fans. Any othersrequired should be indicated on the design draw-ings. Care should be taken to maintain alignmentbetween the fan and the duct connection.

24.6 InsulationIt is practicable to insulate metal bendable duetsbefore erection. Several manufacturers offer theirduets pre-insulated with soft lagging. More com-plicated cutting, bending and jointing techniquesare involved.24.7 Acoustic treabnentPre-insulated duets are also available in specifiedlengths with perforations in the metal to providesound absorption. Special care is'necessary duringinstallation to ensure that the outer casing is madeairtight.24.8 Test holesIt is not practicable to make test holes in flexible,);bendable ducts where readings are required; the ,1test holes should be made in the rigid ductwork. I

25.3 PerformanceFlexible ductwork must meet the standards of air-tightness required by the specification and be with-in the frictional limits specified by the designer.25.4 LengthThe length of flexible duct used in each case shouldbe kept to a minimum, consistent with the parti-cular application.25.5 JointsThese will normally be socket and spigot, withsealant, as for rigid ductwork, and the jointsecured by a worm drive or bolted clipband. Insome cases soft cuffs are bonded to the flexible"ducts. The manufacturer's recommendations as tojointing and sealant should be followed.25.6 SupportsFlexible ducts should be supported in such a waythat kinking ofthe duct is avoided.25.7 Test holesIt is not practicable to make test holes in flexiblefabric duets. Where readings are required, the testholes should be made in the rigid ductwork.

26.3 LengthFleXible joints shall be kept as short as practicableabove a minimum effective length of 50 mm. In no 11case shall a flexible joint exceed 250 rom in length. n26.4 Connections to rectangular ductsWith flanged rectangular connections, the flexiblematerial shall be held in place with flat bar stripsattached to a mating flange (Fig. 167)~For spigot.connections, the flexible material shall be held inplace with flat bar strips (Fig. 168). Flat bar stripsshall be used with proprietary flexible materialhaving sheet metal attached along the edges. Flatbar strips shall De not less than 3 mm thick.

A

I " VII I

+ I II I +I " I

+ I II I + ...•, II I ..I " I

+ I II I +: II III I

.JL_-- --cFjg. 167 Flexible joints-flanged

connection

26.5 Connection to circular and flat oval ductsAdaptors shall be used to provide plain circularends for spirally-wound ducts. Alternatively,flanged connections may be used, adapting themethod set out in 26.4. A sealant in accordancewith the requirements of Section 27 shall be usedbetween the duct and the flexible joint, and thejoint secured by clip-bands with adjustable screwor toggle fittings.

27 SEALANTS, GASKETS AND TAPESFor the purpose of this specification, sealingmaterials and methods are classified as set outbelow.27.1 General propertiesSealants and the other materials covered by thissection, when used in connection with ductwork,shall permanently retain adhesion and e~sticitythrough a temperature range of 0" to 70°C.27.2 Liquid and mastic sealantsAny form of sealing substance applied by brush,trowel or injection gun to a joint formed betweentwo sheets of metal or between sheet and anadjoining member.27.3 GasketsSealant in the form of a pre-formed roll, sheet orstrip applied between opposing faces of flanged orother joints. Gaskets should be not less than 3 mmthick for rectangular ducts up to 1500 mm longerside or circular ducts up to 1250mm diameter; forlarger ducts, the gasket should be not less than 4mm thick.

27.4 Chemical reaction tapeA wrapping which sets through the interaction ofthe activator material and the chemical substancesin the tape, thereby sealing the joint.

II

+ II

+ I +

I+ I

II

+ III

+ I +I 11 1

: + r :: : +I I II I

: + : :: : +-• ••• I.~". --

Fig. 168 Flexible joints - spigotconnection

27.5 Heat-shrinkable band and stripA thermoplastic material, supplied as a continuousband or in strip form, coated on the inside with anadhesive. When heated, the material shrinks to atight fit over the joint. The shrinkage is maintaineduntil the material is reheated.27.6 Self-adhesive tapePVC or other plastic' self-adhesive tape, with orwithout fabric or other reinforcement.27.7 Methods of useThe manufacturer's recommendations and pre-cautions relating to use must be strictly compliedwith.Any form of sealant under compression is morelikely to be successful than a sealing method (suchas tape) applied over a joint. Therefore, a sealantshould, if possible, be applied so as to ensure thatthe air p'ressure within the duct system will cause itto be set into a possible source of leakage ratherthan be blown out of it.

27.7.1 Drying and/or curing periodSolvent based and chemical reaction types ofsealant require a period of between 24 and 72hours for drying or curing, depending on condi-tions. The cure should be completed before theduct is pressurised; otherwise rupture of thejoint is possible.27.7.2 Self-adhesive tapeThe use of self-adhesive tape as a primarysealant is deprecated. It is in practice extremelydifficult to achieve the dry, dust-free andgrease-free surface necessary for the long-termadhesion of such tapes. There is the furtherdisadvantage that where the air pressure in theducts is above ambient, the air pressure isworking against the seal.

28 PROTECTIVE FINISHESFor all normal purposes, protective finishes shallbe as specified by the designer in accordance withthe following. '

28.1 Galvanizing after manufactureGalvanizing after manufacture is not recom-mended for general use. as distortion ofthe duct orfitting is probable, thus making if difficult toachieve an airtight joint. Galvanizing after manu-facture is, however, an acceptable protective finishfor circular pressed fittings.Where galvanizing after manufacture is specified,it shall be to BS 729.

28.2 Metal spra)'ingZinc or aluminium spraying shall be to BS 2569,Part 1.

28.3 Paints28.3.1 Surface preparation and paintapplicationSurface preparation of the metal and paintapplication shall be in accordance with the paintmanufacturer's recommendations.28.3.2 Making good welding damageGalvanizing or other metallic zinc finishdamaged by welding shall be suitably cleanedand painted with one coat of zinc-rich oraluminium paint.28.3.3 -Ducts galvanized after manufactureNo paint protection is required for ducts gal-vanized after manufacture, whether such ductsare installed inside or outside a building.

28.3.4 Ducts made from galvanized sheet or coilDucts made from conventional sheet or coil (see7.2.1) do not require further protection whenlocated inside a building. When located outsidea building, one coat of etch primer or one coatof calcium plumbate primer shall be applied,together with a suitable finishing coat. (But see28.3.6.)28.3.5 Ducts made from other types of mild steelsheetWhere circumstarices require ducts to be madefrom mild steel sheet or coil other than theforegoing, the surfaces shall be adequately pro-tected, as provided in Table 29.The provisions set out in the table are generallyin line with BSI DD .24 - Methods of protectionagainst corrosion on light steel section used inbuilding.28.3.6 Supporting membersSupporting members made of mild steel shall beprotected as provided in Table 30.28.3.7 FoUow-on coatsThe supply and application of the follow-oncoats specified in Tables 29 and 30 together withany additional decorative finishes, are notnormally the responsibility of the ductworkcontractor.As priming coats protect only for a limitedperiod, the follow-on coat or coats should beapplied within the time limit specified by thepaint manufacturer.

Ducts constructedPaint system

from Exposure Primer Follow-oncoats

1 2 3 4

Steel sheet-iron-Indoors None None

zinc alloy coated Outdoors Zinc chromate, calcium Twoplumbate or red oxide

Steel sheet-zinc Indoors Etch primer, zinc Oneelectro-plated chromate or calcium

plumbate

Outdoors Etc~rimer, zinc Twochr ate or calciumplumbate

Black sheet- Indoors Etch primer, zinc Onesprayed zinc or chromate, calcium plumbatesprayed aluminium 0' red oxide

Outdoors Etch primer, zinc Twochromate, calcium plumbateor red oxide

Black sheet- Indoors Zinc rich, zinc chromate Oneother than or red oxidemetal sp.rayed Outdoors Zinc rich or zinc chromate Two

Supporting members Paint systemand other section Exposure Primer Follow-on

coatsJ 2 3 4

Indoors None NoneSteel-galvanized or

Outdoors Etch primer or Twometal sprayedcalcium plumbate

Steel-not galvanized or Indoors Zinc rich, zinc chromate Onemetal sprayed Outdoors or red oxide Two

29 CONNECTIONS TO BUILDER'S WORK29.1 Where metal ducts and fan inlets and outletsconnect to builder's work, connections shall be bybuilt-in timber frame of suitable section or built-incompanion ring or flange. Where metal ductspierce fire barriers, timber frames shall never beused. Companion rings or flanges shall be fixed byan adequate number of suitably sized rag bolts orsimilar fastenings.29.2 In all cases the duct end must be finished witha mating flange where fixed to a timber frame.Where there is no timber frame, the duct shall be

30 ACOUSTIC LININGS30.1 Where a lining to ductwork is required, itshould preferably be fitted at works. Before manu-facture, confirmation should be obtained that thedimenSions of the duct allow for the thickness ofthe lining.30.2 The type of lining, normally glass fibre ormineral wool slab and faced to minimise fragmen-tation and 'fibre-fly', should be approved by thedesigner for type and thickness. Regard should inappropriate cases be had to the fire characteristicsof the material.

30.3 Duct surfaces must be thoroughly clean andthe lining fL'<edby an approved type of adhesive

31 THERMAL INSULATION31.1 The provision and application of thermalinsulation to ductwork is not normalIy the respon-sibility of the ductwork contractor. It should be

Ifome in mind that the application of rigid slabV ~nsulation is more difficult if the duct panels have

been stiffened by cross-breaking or beading.~1.2 Where ductwork is required to be pre-lnsulated, the specification should be agreed with

extended, in the form of a spigoi, beyond theflanged connection and into the builder's work.29.3 Joints between mating flanges and com-panion rings or wooden frames shall be fitted witha sealing gasket (see Section 27).29.4 Where duets are connected to outsidelouvres, the bottom of the duet should be sloped todrain to outside. The inside surfaces of the ductshall be treated as Table 29 for external exposurefor a distance equal to the height of the louvreconnection, or to the nearest plant item.

applied over the whole of the area to be lined. Inaddition, fasteners must be used at 450 mm maxi-mum centres, and not more-than 75 mm from

"Jomts, comer breaks, etc., WIth washers or caps tohold the liriing. In some Clrcumstances metal meshmay be called for by the designer as an additionalprecaution against displacement or- break-up ofthe lining.30.4 The lining must be applied so as to provideabutment at joints and edges, with continuity offacing material. For protection prior to erection,the edges of the lining should be sealed or enclosedby a light metal section mechanically fastened tothe duct.

the designer.31.3 For detailed information on the thermalinsulation of ductwork, reference should be madeto BS 5422: 1977 - Specification for the use ofthermal insulating materials; and BS 5970: 1981-Code of practice for thermal insulation ofpipework.

Part Eight - Appendices

A.I GENERAL CONSIDERATIONSA.I.I Leakage points in ductworkAir leakage in installed ductwork occurs almostentirely at the longitudinal seams and the crossjoints, particularly at the comers, and at the inter-section of the seams and cross joints.A.1.2 Leakage related to duct areaIn practice, leakage can be taken as proportionalto the surface area of the ductwork, whether rec-tangular or circular, even though there may beconsiderable variation in different sections of acomplete system because of the changing sizes ofthe ducts and the number and variety of thefittings. The surface area is easily calculable as partof the design procedure.A.I.3 Pressure/leakage relationshipFor a given pressure, the leakage through anorifice of a given area will vary according to itsshape. With installed ductwork, the leakageorifices are of differing shapes, so a precise valuecannot be given to the pressure/leakage relation-ship. However, Swedish tests on a variety of con-structions have shown that for ductwork operatingwithin the range covered in this specification,leakage can be taken as proportional to pressure tothe power of 0.65. (This value has been adopted byEUROVENT in preparing their Document 2/2 -Air Leakage in Ductwork - see Appendix L - andhas also been adopted in this specification (seeTable 2) and has been applied in Table 31.A.2 LEAKAGE LIMITS - RELATIONSHIPSA.2.1 Limits for each pressure classApplying the values given in Table 2 (page 13), thepermitted leakage at each of a series of pressuresup to the maximum for each class is set out in Table31.

A.2.2 Graphical presentationThe pressure/leakage relationships given in Table31 are expressed graphically in Fig. 169.A.2.3 Leakage as a percentage of airflowAs air leakage is related to surface area of theductwork. it-cannot in advance of the detailed

calculations be expresSed as a percentage of totalairflow, nor will a percentage loss be acceptable asa standard of performance. However, applicationof the leakage limits to a variety of ductworksystems indicates that under operating conditionsair losses will usually be within 6 per cent of totalairflow for the low-pressure class and 3 per cent forthe medium-pressure class. For the high-pressureclass, air loss is likely to be between 2 and 0.5 percent, according to which leakage limit is applied.A.2.4 Special casesThe percentages mentioned in A.2.3 apply tonormal ratios of duct area to airflow; but where theratio is high (e.g., long runs of small ducts), it maybe necessary for the designer to specify a higherstandard of airtightness in order to keep the actualleakage within an acceptable limit.A.2.5 Designer's required calculationsDesigners will be concerned with the total loss ofair through leakage which must be allowed for theductwork, and will need to:

(a) calculate the pressure class;(b) calculate the surface area and estimate the

mean system pressure difference for theductwork system (or part of system);

(c) calculate the total leakage using the appro-priate rate from Table 31.

Alternatively, the designer may:(d) decide on the maximum total leakage that

he can accept;(e) calculate the surface area and estimate the

mean system pressure difference for theductwork system (or part of system) andfrom these determine the required pres-sure class.

A.2.6 Leakage or complete systemOW/142 deals only with the ductwork. The leak-age characteristics of plant items and accessoriesare not within the control of the ductwork con-tractor, and therefore any leakage limits and leak-age testing called for under DW/142 shall beunderstood to apply only to the ductwork itself.

Maximum leakage of ductworkStatic

p'ressure Low-pressure Medium-pressure High-pressuredifferential Class A Class B

ClassC CassO

1 2 3 4 5

Pa Litres per second per square metre of surface area

100 0.54 0.18

200 0.84 0.28

300 1.10 0.37

400 1.32 0.44

500 1.53 0.51

600 0.58 0.19

700 0.64 0.21

800 0.69 0.23

900 0.75 0.25.1000 0.80 0.27

1100 0.29 0.10

1200 0.30 0.10

1300 0.32 0.11

1400 0.33 0.11

1500 . 0.35 0.12

1600 0.36 0.12

1700 0.38 0.13

1800 0.39 0.13

1900 0.40 0.14

2000 0.42 0.14

2100 0.14

2200 0.15

2300 .0.15

2400 0.16

2500 0.16

='i 0.25..llI:

3

~~~

~:q;~~o

~~1I\~1>\~ Y

•••

I'

=~ 1.75

t02au~.ae~ 1.25

e~=i 1.0•..~'l:lS 0.75

~lrl 0.5

~

~ ~ ~ ~ ~ ~ ~ ~ ~Pressure difference in pascals

e=t02 0.40

a....~ 0.35'l:lei 0.30

e=&0.25<II•..:0.20

I•.• 0.15

~

~ 0.10

,5~().05=..llI:=~

~.c:c'"~.,.~

1"'~~~u~ I

~'l)'~EC\.

tUG" \' .

1000 1150 1500 1750

Pressure difference in pascals

Part Eight - Appendix A - continued

Fig. 170 Leakage as percentage of airflow~

1/ ~ ~1000 ./ / 600800 ./ ~ ,;i'

200 800 2000[/1-" / !!!!..

...,400 ~~ ./ V

1000100

800 >80 ./ V200 800"" / ."60

~7olI-- ./ ~ 8040100 / > V 1/ 1/

./ I llo"!' ./>/ 6080 : ! : I -/ ~

20 60 200!~ ,- I I-" !L./ I.,,;

VT""

,. ,.,.40 I-" /1

10100~-- -

8 80I

20 60 ./. I /6 / ./ /,

• 40

10 1/

A /8 ,rI

2 620 /" I,.

I-

Y1• ~j."10

<l lDC

, !, I ! , I , t I I

~In In 200 400 600 800 1000 2000In In

d d ~<l.

LEAKAGE (LIs) MEAN DIFFERENTIAL PRESSURE (Pal

Mean differential pressure .Duct area .Airflow .

Maximum permitted leakage .Percentage of airflow .

Based on charts prepared by EUROVENT.reproduced by kind permission.

91.84.58

Example rClass A320Pa80m2

2m3/s

,/.I ~ VI/ ~

VVI/.I ,0~

:/ .I.I .I 1/

I I

!J A,/ / 1/ :

40/

If,/ ,/ v ,

20 V /.1 V / I V'/ /.1 I V 1 ,

Vj / / !"I / ,10 ./ / /:l: I

6 : I,/ 1/ i

4

i ,,/, I I

2V ./ I :/ I

I I

,V II

CLASSA ~, ! r I r , I, I , ,

3 4 5 6 i 8 10CLASSB I ! I ! I , ! ! I

1 2 ~ 4 5 6 8CLASSC

, , "! !I ! ! I005 1 2 3 4

PERCENTAGE LEAKAGE

Example 2ClassBSOOPa200m2

6m3/s

Chartreading

924.6

Chartreading

1392.3

138.82.31

B.l GENERALSection 6 (page 13) of this specification deals withthe performance req~irements of ductwork inrespect of air leakage, and Table 31 (Appendix A)tabulates the limits of leakage applicable to eachclass of ductwork. Appendix B is solely concernedwith recommendations for the testing procedure.B.2 Extent of ductwork to be tested

B.2.1 The procedure set out in this section islimited to the ductwork. Terminal connections,and items such as air handling devices, terminalboxes, sound attenuators, heat exchangers,Duilder's work construction, are excluded fromthe tests.B.2.2 The proportion of the ductwork to betested and the method of selection (where notincluded in the job specification) should bedetermined in collaboration between thedesigner and the ductwork contractor. Wherethe method is by random selection, the use ofpolythene sheet or similar insertion blanks be-tween duct cross joints and duct-mounted com-ponents will assist in avoiding delays in instal-lation when tests are being carried out.B.2.3 To enable the blank to be cut out after thetesting is completed, access may be requiredadjacent to each blank. This procedure used oneither side of a duct-mounted component willenable the component to be included in a sub-sequent additional test if specified.B.2.4 Alternatively, rigid removable blankingplates can be used, although this involvesremaking joints.

B.3 Testing to be completed before insulation, etc.Testing shall be satisfactorily completed beforeinsulation or enclosure of the ductwork and beforeterminal units (if any) are fitted.

B.4 Retesting procedure where DecessaryB.4.1 The air leakage rate for any section shallnot be in excess of the permitted rate for thatsection. If a first test produces leakage in excessof the permitted maximum, the section shall beresealed and retested until a leakage not greaterthan the permitted maximum for that section isachieved.B.4.2 If at the time of witnessing the test it isapparent that excessive additional sealing ofseams or joints has been done in order to meetthe required leakage level, the section of duct-work under test shall not be counted as part ofthe tested ductwork, except where the whole ofthe ductwork is required to be tested.

B.5 Minimum area to be testedThe section of ductwork to be tested shall have anarea large enough to enable the test apparatus toregister a measurable leakage.B.6 Test pressures and leakage ratesThe maximum permissible leakage rates for thefull range of pressures are given in Table 31. Therecommended test pr~ssures for the various classesof ductwork are set but in Table 32, and unlessotherwise specified, the choice of test pressureshall be at the discretion of the test operator.

StaticMaximum leakage of ductwork

pressure Low-pressure Medium-pressure High-pressuredifferential Class A Class B

Class C Class D1 2 3 4 5

Pa Litres per second per square metre of surface area

200 0.84400 1.32 0.44800 0.69

1200 0.301500 0.35 0.122000 0.14

B.7 Test apparatusB.7.1 The accuracy of the test apparatus shallbe within:

± 10 per cent of the indicated flow rate, or0.4 litres per second, whichever is thegreater; and± 5 per cent at the indicated static pressurein the duct under test.

B.7.2 The test apparatus shall be inspected bythe user before use on site, and shall have acahbration certificate, chart or graph dated notearlier than one year before the test for which itis used.B.7.3 A diagram of a suitable test apparatus isgiven in Fig. 171.

B.8 ProcedureB.8.1 The section of ductwork to be tested forair leakage shall be sealed. Main ducts shouldbe provided with flanged joints to enable blank-ing plates to be fitted, while small open endsmay be sealed with polythene or inflatable bags,which should be left in position until final con-nections are made.B.8.2 On low-pressure systems, final grillespigots made as a second fix operation shall beexcluded from the test. The joint shall, wherepracticable, be checked by external visualexamination.B.8.3 Sufficient time shall be allowed betweenerection and leakage testing for sealants to cure.B.8.4 Special care must be exercised in making

all joints which fall outside the scope of thetesting procedure, i.e., joints between testedsections of ductwork and between ductworkand other units.B.8.5 Due notice of tests shall be given, so thatarrangements for witnessing the tests, ifrequired, can be made.

B.9 Testing sequenceThe recommended sequence of testing is asfollows.

B.9.1 Complete Part 1of the Test Sheet.B.9.2 Connect test apparatus to section of duct-work to be tested.B.9.3 Adjust test apparatus until the staticpressure differential is obtained.B.9.4 Check that the measured leakage is with-in the permitted rate. (No addition shall bemade to the permissible leakage rate for accessdoors, access panels or dampers where these areincluded in the ductwork.)B.9.5 Maintain the test for fifteen minutes andcheck that the leakage rate has not increased.B.9.6 Reduce pressure in section to zero byswitching off the fan; then immediately re-applytest pressure to establish that the air leakagerate is not greater than the previous reading.B.9.7 Record details on Part 2 of the Test Sheetand complete, including witnessing.

B.I0 Air leakage test sheetA specimen of a suitable Test Sheet is given onpage

Blanking/plate

Flow measuring device(may be located onthe suction side of "'-the fan) "'

Bleed valve (not necessaryif variable speed

/fanused)

Duct testpressure gauge-

Electricallydriven fan

Attention is drawn to HVCA pubUcation DW1143 - A PracticalGuide to Ductwork Leakage Testing - which gives detailedadvice on the actual procedure for ductwork le.tkage testing.

Specimenof air leakale test sheet

GeneralName of job , '" .

. .

Building reference .

P¥t 1- Physical details

a Section of ductwork to be tested· .

b Surface area of duct under testt : .

c Test static pressure ; ~.'

d Leakage factor .

e Maximum permitted leakage (b x d) titres/sec.

Part 2 - Test particulars

a Duct static pressure reading .

b Type of flow measuring device .

c Range of measurement of flow measuring device .

d Reading of flow measuring device : .

e Interpreted air flow leakage rate .

f Duration of test (norm~y 15minutes) .

Date of test Carried out by................................. Witnessed by .

Length Width and depth Periphery Areaor diameter

metres millimetres millimetres square metres

rrOTAL

NoteThe information given in this Appendix is for theguidance of mechanical service contractors, con-sulting engineers, etc. The identification of duct-work does not form part of the work carried out bythe ductwork contractor unless called for in the jobspecification.

C.l GE~ERALC.1.1 IntroductionWith the increasing complexity of ventilation andair conditioning systems, it is becoming moreimportant to ensure ready identification of ductsfor the purposes of commissioning, operation andmaintenance of systems. The purpose of theserecbmmendations is to lead towards the use andstandardisation of a system of identification forducts for the benefit of designers, contractors andclients.C.1.2 Scope

C.1.2.1 These recommendations deal with theidentification of ducts for ventilation, air condi-tioning and simple industrial exhaust systems.They. do not include piped gas systems such asare dealt with in BS 1710, nor with ductworksystems for industrial processes, although thegeneral considerations and intentions could beextended with the agreement of the client tocover such systems.C.l.!.l The method is designed to identify theair being conveyed, the direction of flow, thedestination of the air and/or of the plant wherethe air was treated. With small or simple plants,it may not be strictly necessary to provide iden-tification because the function is apparent, butit is considered advisable to do so because thiswill increase familiarity with the labellingsystem and also because the nature and direc-tion of air flow may not always be apparent.

C.2 IDE~TIFICATION

C.2.1 LocationTo be effective the identification must be placedwhere it can be easily seen and at positions whereidentification will be required. To ensure that thesymbols are seen, the following points should beconsidered.

C.2.1.1 The symbols should be on the surfaceswhich face the positions of normal access to thecompleted installation.C.2.1.2 The symbols should not be hiddenfrom view by structural members, other ducts,plant, or other services distribution systems.C.2.1.3 The symbols should be placed wherethere is adequate natural or artificial light.

C.2.2 Identification symbols will be neededmainly in the plant room. Symbols should occurfrequently enough to avoid the need for ducts to betraced back. Symbols should be placed at any ser-vice and access points to the distribution system,including points where the distribution system hasreduced to a single duct.C.2.3 Colour codingThe choice of colours has been based on the needto provide:

C.2.3.1 Strong contrasting colours which arerecognisable even though covered with dust.C.2.3.2 Contrast between the symbol colourand the base colour of the duct. Usually the basecolour metallic grey of galvanized or aluminiumsheet or foil sheathing, or the white, pale grey,or buff paint on the insulation is a neutral colouragainst which the recommended symbol colourswill stand out.

C.2.4 The recommended colours are given inTable 33. The colour coding indicates the type ofair being conveyed.

Type Colour BS 4800

/ 2 3

Conditioned air Red and 04 E 53Blue 18 E 53

Warm air Yellow 10 E 53

Fresh air Green 14 E 53

Exhaust/extract/recirculated air Grey AA009

Foul air Brown 06 C 39

Dual duct system-hot supply air Red 04 E 53

Dual duct system-cold supply air Blue 18 E 53

C.2.S For conditioned air, two symbols (one red,one blue) may be used, or a single s~bol colouredpart red, part blue.C.2.6 If a finer grading than that given in Table 33is required, as for instance in a laboratory with twoseparate contaminated air exhaust systems, it isrecommended that the type colour be used with,say, a stripe of a second colour. Where the ductcontents constitute a hazard, a symbol as given inBS 1710 should be added to the type colour.

C.2.7 Direction of flowC.2.7.1 The form of symbol chosen indicatesdirection. It is an equilateral triangle (see Fig.172) with one apex pointing in -the direction ofair flow. Where the boundaries of the duct arenot visible, two triangles should be arranged inline ahead to indicate direction of flow.C.2.7.2 The size of the symbol will depend onthe size of the duct and the viewing distance.The recommended minimum size for normaluse is 150 mm length of side.

Fig. 172 Example of duct identificationsymbol

Direction -+of flow

C.2.S Further identificationC.2.S.1 On small or simple installations wherethere is one plant and one or two zones andtherefore little chance of confusing the ducts, itwill not be necessary to provide identificationother than the colour symbol. On large complexinstallations with many zones, widely brancheddistribution systems or several plants, furtheridentification is necessary. In this connection aplant refers to the ductwork and equipmentassociated with one particular fan.C.2.S.2 The further information to be givenwill normally be the space served by the ductand in some cases the associated plant. Theinformation should be given as briefly as pos-sible using commonly accepted forms such as anumber indicating which floor of a building.The plant identification should always be pre-ceded by the letter 'po to avoid confusion be-tween the number of the floor and the number

of the plant. The plant itself must be clearlynumbered to correspond. Letters for Supply,Flow, Extract, etc., should not be added be-cause identification will be clear from the coloursymbol. Thus confusion between '5' for Supplyand '5' for South will be avoided.

Table 34 Examples of further identiftcationsymbols

Code Information given

9 SW P2 9th Floor,South-West Zone,Plant Two

Comp 2 P2 Computer 2,Plant Two

3 Lab S P4 3rd Floor,Laboratory 8,Plant Four

2 Op Th 2PI 2nd Floor,Operating Theatre 2,Plant One

Bay 5 N P5 Bay 5, North end,Plant Five

C.2.8.3 Where identification of the space is byroom number, this must be agreed with the userwho otherwise may have numbered the roomsdifferently.Some examples of further identification systemsare given in Table 34.C.2.8.4 The letterS and numbers should be ineither black or white, whichever gives the bettercontrast. They should be marked on the coloursymbol or immediately adjacent to it. The sizeof the figures will depend on how easily they canbe seen, but should not be less than 25 mm high.

C.2.9 Explanatory chartIt is recommended that an explanatory chartshould be kept in the plant room or other con-venient place. The chart should show and explainthe colour symbols used on the installation andwhere appropriate the figure and letter codes usedfor further identification.

C.3 METHOD OF APPLICATION OFSYMBOLS

C.3.1 Several methods are available for applyingthe symbols, the main factor being that the symbolis permanently affixed. Suitable methods are:

C .3.1.1 Painting, using stencilled letters andfigures.C.3.1.2 Self-adhesive plastics or transfers withwater soluble backing. (It is important to ensurethat the surface is smooth and clean and that theadhesion will not deteriorate due to the sur-rounding atmosphere.)C .3.1.3 Purpose-made plastics or metal labels.

APPENDIX D - TRANSPORT, HANDLING AND STORAGEOF DUCTWORK

0.1 TransportLarge capacity vehicles such as furniture vans orsimilar, with high-sided open or closed top bodies,are the most suitable for the transport ofductwork.0.2 Lengths of ductwork should preferably be;positioned so as to avoid crushing. Lengths withprojections, such as branches and bends, flanges,girths, damper quadrants, etc., should be packedso as to avoid damage to adjacent duct panels. Insome cases, particularly on contracts calling forrepetitive sizes, the use of timber jigs and spacersmay be justified.0.3 Where reduced bulk and greater protectionare major factors, such as consignments forexport, transporting ductwork in 'L' shape sec-tions may justify the increased site assembly costs.

0.4 HandlingSheet metal ducts are liable to deformationthrough careless or excessive handling. Suchdeformation does not normally affect function, butwill detract from appearance.

D.S To minimise damage, duct sections should beclearly identified, and deliveries to site should beclosely linked to the installation programme, so asto avoid accumulation of unfixed ductwork anddouble handling.

0.6 StorageAdequate floor space must be provided for the sitestorage of ductwork. Such storage shall make dueallowance for the storage of ductwork in stackssuch that access between the stacks is of sufficientwidth to permit the removal of items from onestack without interference to adjoining stacks.

Lengths of ductwork should preferably be posi-tioned so as to avoid crushing. Ductwork of smallpanel size may be stored horizontally; however,care should be exercised to ensure that stack sizesare limited to within the structural strength of theduet sections to prevent distortions of the lowersections within the stack.All ductwork should be stored so as to preventwater collecting, clear of ground water and in com-pounds free from site traffic.All storage facilities shall be covered and ade-quately protected against rain and snow. Wheretarpaulins are provided as temporary cover, theyshould be held clear of the ductwork so that air cancirculate, and secured in such a manner as toimpose no direct load on the ductwork.Covered storage is important to minimise theformation of the unsightly deposit known as 'whiterust', which is a corrosion product formed on thezinc surface where it is in contact with water for along period from rain or condensation.While the protective properties ofthe zinc are notimpaired by the presence of superficial white rust,it is unsightly and this can result in a rejection ofthe ductwork so affected.Small areas of white rust can be removed by abrad-ing with a stiff bristle brush. Larg~ areas can betreated by various proprietary products designedfor this purpose, or by simple chemical solutionswhich can be prepared on site.Moving parts, such as damper spindles, and acces-sories liable to corrode, should be greased orotherwise adquately protected. On removal fromstorage, all ductwork and fittings, etc., should beinspected and clean.ed of extraneous materials.

E.I Fire containment and fire hazards are factorswhich influence the design and installation of duct-work systems. Information concerning the fireprotection of ductwork can be found in CP 413published by the British Standards Institution andin the Technical Memorandum 1 published by theChartered Institution of Building Services(formerly the Institution of Heating and Venti-lating Engineers). Notes on legislation relating tofire and services in buildings are given in CIBSTechnical Memorandum 2.E.2 The principles of fire protection in relation toductwork are:E.2.1 Fire dampers should be provided whereducts pass through fire compartment walls. Firedampers should be framed in such a way as to allowfor expansion in the event of fire, and the designmust provide for the protection of any packingmaterial included.

E.2.2 If there is no duct opening into the com-partment, fire dampers may be omitted at thewalls, provided the duct is enclosed by a structurehaving the same fire resistance as the compart-ment. In this context, it should be appreciated thatsheet metal alone offers only limited fire resistanceand is not a heat barrier.

E.2.3 The amount of combustible and smoke/fume producing materials used in the constructionof ductwork should be limited. This requirementincludes in its scope sealants, gaskets and otherjointing materials; flexible ducts and joints, insula-ting and lining materials. The combustible content'of Construction material is assessed by the firepropagation test specified in BS 476, Part 6.

Standard types of fire dampers and frames aredescribed in Section 23 of this specification.

F.l GeneralF.1.1 For galvanizing after the fabrication of anyarticle it is necessary to appreciate the nature ofthe process, including the surface preparation ofthe object to be treated and the precautions to betaken in design, fabrication and handling.F.1.2 Galvanizing involves dipping the object intoa bath of molten zinc (at a temperature of between445° and 465°C), and it is necessary for the zinc tocover the whole of the surface leaving no gaps inthe zinc.F.2 Design and fabricationF.2.1 It is well known that fabrication articles willsuffer distortion in the course of dipping into themolten zinc bath, due to the introduction of orrelief of inherent stress in the steel sheet or of anystresses that may have been built into the itemduring fabrication, or indeed of any stresses intro-duced during the handling, loading or unloading ofthe item. The sheet thicknesses specified inDW/142 for articles to be galvanized after manu-facture are calculated to take this factor intoaccount.F.2.2 It is essential to have a free flow of themolten zinc over the object to be galvanized, to-gether with quick and complete drainage of themolten metal. Because of the high temperatureinvolved, the object to be galvanized should be asrigid as possible, either by the use of sufficientlyheavy sheet or by stiffening or bracing, or both.F.2.3 Any sealed hollow section must be ade-quately vented in order to obviate any possibilityof explosion. Holes in vertical members must beprovided diagonally opposite each other, top andbottom of the member.F.2.4 Vent holes should be of sizes as follows:

Size ofhollowsection

(dia. or side)

Diameter ofvent anddrainage

holes

mmUp to 2550 to 100100to 150Over 150

mm8 (never less)

102025

F.2.5 Stiffeners should desirably have theircomers cropped so as to allow a free flow of zinc.Stiffeners should be rolled steel angle, uncoated.

F.3 Surface preparation before galvanizingF.3:1 The steel surface to be galvanized must bechemically clean before dipping. This is mainlyachieved at the galvanizer's works by pickling in anacid bath and washing before the article goes intothe zinc bath. However, the pickling process doesnot remove grease, oil or oil-based paint, and suchsubstances should be removed by the fabricator bythe use of suitable solvents before the object to betreated is delivered to the galvanizing works. Anysurface rust that develops on the object betweenthe time of treatment by the fabricator anddelivery to the galvanizing works is not important,as this is cleaned off by the acid pickling process.

F.4 Handling and storage after galvanizingF.4.1 While a galvanized surface will not developrust in the ordinary sense as long as the zinc coatingis undamaged, zinc is subject to what is known as'white rust,' which is an unsightly and damagingdeposit on the zinc surface. White rusting can arisefrom the stacking of articles when wet, acidvapours, the effect of salt spray, the reaction ofrain with flux residues, etc.

F .4.2 Galvanized articles should therefore not bestacked or loaded when wet; they should desirablybe transported under cover or shipped in dry, well-ventilated conditions, inserting spacers (but notresinous wood) between the galvanized articles.

F.4.3 When stored on site or elsewhere, careshould be taken to avoid resting the galvanizedarticle on cinders or clinker, as the acid content ofthese substances will attack the zinc surface.

F.5 Subsequent finishingF .5.1 Paint finishing subsequent to galvanizing issometimes required either for additional protec-tion or for decorative reasons. It should be notedthat the adhesion of paint coatings to new gal-vanized surfaces is suspect, and either the appli-cation of a calcium plumbate based primer directto the galvanized surface, or a phosphating treat-ment, is recommended. Advice should be soughtfrom the paint manufacturer.

The above is based on information given inpublications available from theGalvanizers' Association,34 Berkeley Square, London WIX 6AJ(Telephone: 01-499 6636)

G.I GeneralG.I.I Stainless steel is not a single specificmaterial: it comprises a group of steels with vary-ing composition, but in no case less than 9 per centof chromium. It is the chromium addition whichprovides the enhanced corrosion resistance ofstainless steels.G.1.2 Modem stainless steels have a combinationof good formability and weldability, and can besupplied with a variety of surface finishes (seeG.4.1 below). They have been developed to covera wide range of structural uses where high resis-tance to corrosion and low maintenance costs aredemanded.G.I.3 Ductwork applications for which stainlesssteels are particularly suited include those where ahigh integrity inert material is essential; where ahigh degree of hygiene is required; in the chemicalindustries where toxic or hazardous materials maybe contained; in nuclear and marine applications(e.g., on offshore platforms). Stainless steels alsofind application in exposed ductwork where theirfinish can be used to aesthetic advantage.G.2 Grades of stainless steelG.2.1 The grades of stainless steel used for duct-work applications are among those covered by BS1449, Part 2. Before a type is specified, the natureof the environment, fabrication requirements,etc., should be taken into account. The types usedfor ductwork could be the ferritic 400 series(magnetic) or the austenitic 300 series (non-magnetic). The latter contains nickel as well aschromium, and offers the better corrosionresistance.G.2.2 Some typical stainless steels and theircharacteristics are described below.

G.2.2.1 Type 409 - 11.5% chromium; 0.3%titanium ('Hyform')This is a ferritic stainless steel developed as astainless steel type lower in price than someothers, and with forming characteristics similarto those of mild steel. Type 409 is non-hardening by the heat from welding; does notrequire post-weld treatment; and can be formedusing conventional practices.It is used in mildly corrosive environments, e.g.,domestic boilers; automotive exhaust parts; anda wide range of structural applications.G.2.2.2 Type 304 - 18% chromium; 9% nickel('Austenitic')This type is sometimes referred to as '18/8', i.e.,18 per cent chromium and 8 per cent nickel,although the actual composition may varywidely from those figures. It is weldable and hasgood formability with good general corrosionresistance.It is used in moderately corrosive environ-

ments, storage tanks, process plants, roadtankers, etc.G.2.2.3 Type316-17%chromium; 11%nickel;2.5% molybdenum ('Austenitic')This type has very high corrosion resistance andis weldable.It is particularly useful in aggressive environ-ments such as process plants; marine applica-tions; power generation; etc.

C.3 AvailabilityG.3.1 Stainless steel is supplied in a wide range ofthicknesses, from 0.4 mm for cold-rolled sheet andcoil, and from 0.075 mm for precision rolled strip.It is supplied in slit widths as specified by thecustomer, up to a maximum width of 1525mm.

G.4 Surface finishesG.4.1 Stainless steel is available in a wide selec-tion of finishes, varying from fine matt to mirrorpolished, as defined in BS 1449: Part 2:

MillftnishesType 2D Cold finished, softened and

descaled. A uniform matt finish.Type 2B Cold rolled, softened, descaled and

lightly worked with polished rolls. Asmooth finish brighter than 2D.

Type 2A Bright annealed. A cold finishedreflective appearance retainedthrough annealing.

Polished finishesType 4 Dull polished. A lustrous uni-

directional finish produced by finegrinding, generally with abrasives of150 grit size. It has little specularreflectivity. Further dull polishingafter fabrication will diminish theeffects on appearance of welds oraccidental damage by blending theminto the surrounding metal.

Type 8 Mirror polished. A bright reflectivefinish with a high degree of imageclarity.

C.4.2 Where other finishes are required, such asfor aesthetic purposes, colour may be applied inthe form of paint or lacquer, or the material maybe supplied pre-co loured as by the 'INCO'process.

G.5 Surface protectionG.5.I No surface protection is required for stain-less steel ductwork used indoors or outdoors, pro-vided the correct quality is specified. This i~ be-cause the naturally occurring chromium-rich oxidefilm which is present on the surface of the metal, ifdamaged, reforms immediately by reaction be-tween the steel and the atmospheric or othersource of oxygen.

G.I GeneralG.!.l Stainless steel is not a single specificmaterial: it comprises a group of steels with vary-ing composition, but in no case less than 9 per centof chromium. It is the chromium addition whichprovides the enhanced corrosion resistance ofstainless steels.G.I.2 Modem stainless steels have a combinationof good formability and weldability, and can besupplied with a variety of surface finishes (seeG.4.1 below). They have been developed to covera wide range of structural uses where high resis-tance to corrosion and low maintenance costs aredemanded.G.!.3 Ductwork applications for which stainlesssteels are particularly suited include those where ahigh integrity inert material is essential; where ahigh degree of hygiene is required; in the chemicalindustries where toxic or hazardous materials maybe contained; in nuclear and marine applications(e.g., on offshore platforms). Stainless steels alsofind application in exposed ductwork where theirfinish can be used to aesthetic advantage.G.2 Grades of stainless steelG.2.1 The grades of stainless steel used for duct-work applications are among those covered by BS1449, Part 2. Before a type is specified, the natureof the environment, fabrication requirements,etc., should be taken into account. The types usedfor ductwork could be the ferritic 400 series(magnetic) or the austenitic 300 series (non-magnetic). The latter contains nickel as well aschromium, and offers the better corrosionresistance.G.2.2 Some typical stainless steels and theircharacteristics are described below.

G.2.2.1 Type 409 - 11.5% chromium; 0.3%titanium ('Hyform')This is a ferritic stainless steel developed as astainless steel type lower in price than someothers, and with forming characteristics similarto those of mild steel. Type 409 is non-hardening by the heat from welding; does notrequire post-weld treatment; and can be formedusing conventional practices.It is used in mildly corrosive environments, e.g.,domestic boilers; automotive exhaust parts; anda wide range of structural applications.G.2.2.2 Type 304 - 18% chromium; 9% nickel(' Austenitic')This type is sometimes referred to as '18/8', i.e.,18 per cent chromium and 8 per cent nickel,although the actual composition may varywidely from those figures. It is weldable and hasgood formability with good general corrosionresistance.It is used in moderately corrosive environ-

ments, storage tanks, process plants, roadtankers, etc.G.2.2.3 Type 316 - 17%chromium; 11%nickel;2.5% molybdenum ('Austenitic')This type has very high corrosion resistance andis weldable.It is particularly useful in aggressive environ-ments such as process plants; marine applica-tions; power generation; etc.

C.3 AvailabilityG.3.1 Stainless steel is supplied in a wide range ofthicknesses, from 0.4 mm for cold-rolled sheet andcoil, and from 0.075 mm for precision rolled strip.It is supplied in slit widths as specified by thecustomer, up to a maximum width of 1525mm.

G.4 Surface finishesG.4.1 Stainless steel is available in a wide selec-tion of finishes, varying from fine matt to mirrorpolished, as defined in BS 1449: Part 2:

MillftnishesType 2D Cold finished, softened and

descaled. A uniform matt finish.Type 2B Cold rolled, softened, descaled and

lightly worked with polished rolls. Asmooth finish brighter than 2D.

Type 2A Bright annealed. A cold finishedreflective appearance retainedthrough annealing.

Polished finishesType 4 Dull polished. A lustrous uni-

directional finish produced by finegrinding, generally with abrasives of150 grit size. It has little specularreflectivity. Further dull polishingafter fabrication will diminish theeffects on appearance of welds oraccidental damage by blending theminto the surrounding metal.

Type 8 Mirror polished. A bright reflectivefinish with a high degree of imageclarity.

C.4.2 Where other finishes are required, such asfor aesthetic purposes, colour may be applied inthe form of paint or lacquer, or the material maybe supplied pre-co loured as by the 'INCO'process.

G.5 Surface protectionG.5.1 No surface protection is required for stain-less steel ductwork used indoors or outdoors, pro-vided the correct quality is specified. This i~ be-cause the naturally occurring chromium-rich oxidefilm which is present on the surface of the metal, ifdamaged, reforms immediately by reaction be-tween the steel and the atmospheric or othersource of oxygen.

G.S.2 If a mixture of metals is used, such as mildsteel supports for stainless steel ductWork, the sur-face of the mild steel must be adequately protectedfrom the galvanic corrosion that might result fromthe intimate contact between the two types ofmetal. (The appropriate protective finish in Table29 (for outdoor applications) should beemployed.)

G.6 ConstructionG.6.1 Sheet thicknesses for stainless steel duct-work should be the same as for galvanized steel(see Tables 4, 14 and 15). Where any additionalgauge allowance is made for corrosion resistan~e,this should be based on knowledge of the corrosiveinfluences present in the local environment.G.6.2 The fonning of rectangular and circularducts can be carried out by the use of conventionalpress working and sheet metal forming machines.Some alteration in working practices may benecessary, however, depending on the type ofstainless steel being used.G.6.3 As a general rule, the 400 series ofstainlesssteels can be formed using normal mild steel set-tings. The 300 series, however, because of thehigher yield point and the greater rate of workhardening, will require higher working pressures.G.6.3 Ductwork contractors who have experienceof the use of stainless steel report difficulty informing Pittsburgh and button punch snap lockseams. As regards cross joints, socket and spigotjoints are recommended, and one or two of theslide-on'flanges are suitable. In view of the fore-going, it is recommended that trials be carried outbefore starting on production.

G.7 Rectangular ductsThe constructional requirements for rectangularstainless steel ducts are the same as for galvanizedmild steel.

G.8 The constructional requirements for circularstainless steel ducts are the same as for galvanizedmild steel.

G.9 StiffeningWherever possible, the material used for stiffeningshould be of the same grade of stainless steel asused for the construction of the ducts, or should bemade equally corrosion resistant to suit theenvironment in which the ductwork is situated.

G.10 Flxings and fasteningsThe types of fastening and the maximum spacingsspecified in Table 10 (rectangular) and Table 16(circular) also apply to stainless steel ductwork.Fixings and fastenings should be of the appropriategrade of stainless steel as used in the constructionof the ductwork, or should be made equally resis-tant to corrosion in relation to the environment inwhic.h the ductwork is situated. The type of stain-less steel fastening used should conform to theappropriate specification (e.g., BS 1768, 3692;ISO 3506 - Hexagon bolts, set screws and nuts).G.l1 WeldingAll the modem welding processes may be used toweld stainless steel, but tungsten inert gas (TIG)and resistance welding are likely to be the mostsuitable for light-gauge materials. Attention isdrawn to BS 4872: Part 1 when welding stainlesssteels; and to BS 2901 for the selection of filler rodsand wires.When welding dissimilar metals, e.g., mild steel tostainless steel, the choice of the electrode is veryimportant, as the effect of dilution of the weldmetal by the base metal must be considered.Reference should be made to BS 2901: Parts 1 and2, and to BS 2926 for selection of weldingelectrodes.G.12 Fire dampersStainless steel is an ideal material for use in theconstruction of fire dampers, due to its high resis-tance both to heat and corrosion. It is thereforemost applicable where a fire authority makes cor-rosion resistance a requirement.G.13 Sealants, gaskets and tapesThe sealing materials and methods set out in thisspecification are also applicable to stainless steelductwork. However, any chloride-based material,such as polyvinyl chloride (PVC), should beavoided, as breakdown of such materials at certainelevated temperatures could lead to corrosion ofthe stainless steel.G.14 General design considerationsIt is the designer's responsibility to indicate thetype of stainless steel most suitable for the condi-tions in which the ductwork is to be exposed. Ifusers and designers are in doubt as to whichmaterial is appropriate to a particular application,technical advice may be obtained from the sourcenoted below.

This appendix is based largely on informationkindly supplied by theBritish Steel Corporation,Stainless Steel Advisory Centre,P.O. Box 161,Shepcote Lane,Sheffield S91TR(Telephone: 0742 440060/441224)

H.l Nature of the materialH.l.l 'Pre-coated' steel is sheet, coil or strip towhich has been applied at the steel mills a coatinghaving a decorative or protective function, orboth.H.1.2 The basis metal to which the coatings areapplied are hot-dip galvanized sheet or coil,uncoated steel or electro-galvanized steel (e.g.,Zintec).H.2 Range of coatings availableH.2.1 A number of different types of coating, invarious thicknesses, are available - PYC('plastisol' and 'organosol'); paint coatings ofseveral types, silicone enamels, etc.H.2.2 A wide range of colours and surface finish-ed are available, but there are minimum quantityrequirements for some types of coating, finish andcolour. The characteristics of the particular type ofcoating contemplated for a particular use shouldbe investigated in respect of formability, fastnessto light, chemical resistance and other relevantproperties.H.2.3 The material can be supplied with one orboth sides treated.H.3 Sizes availableH.3.1 Pre-coated steel is available in sheet or coilform - sheet in widths from 610 mm to 1370 mmand in length up to 5486 mm. Coil is supplied inwidths from 610 mm up to 1370 mm. The maxi-mum available width can vary also according to thesteel thickess required. Availability varies accord-ing to type of substrate and coating, so prospectivepurchasers should query the sizes available for thespecific type required.H.4 Sources of supplyH.4.1 Pre-coated steel is obtainable from majorsteel stock-holders or direct from the British SteelCorporation.

H.5 Ductwork construction from pre-coated steelH.5.1 The type of pre-coated steel most suitablefor ductwork should be carefully considered.mainly from the point of view of the fabricationproperties of the coating type. It is probable that aplastisol coating will be found to be most suitablefor ductwork, as this type of coating will withstandan Ot bend at normal ambient temperatures. Italso tolerates rougher handling during formingand erection than the much thinner paint coatingtypes.H.5.2 Careful consideration should be given tothe constructional methods to be used for duct-work to be made from pre-coated steel. Theprinciple to be followed should be to make seamsand joints as unobtrusive as possible. Some of theconventional methods of seaming may be used,but a number of others are not suitable. Weldingwith conventional equipment should not beattempted. Mechanical fastenings should bechosen with care having regard to appearance aswell as efficiency; and sealant should be appliedwith these factors in mind. Stiffening should becarefully considered in relation to appearance.H.6 Handling, storage, transport and erectionH.6.1 Much more care than usual is required inthese respects, as the coatings are all to a greater orlesser degree susceptible to mechanical damage.For example, sheet should not be dragged off thetop of a pile but removed by 'turning' off the stack.H.6.2 With sheet pre-coated on one side only, itmay be found desirable to stack face to face.H.6.3 The flexibility of coatings of the types usedon pre-coated steel depends on temperature.Therefore, manipulation should be carried out attemperatures above 16°C (60~) in order to pre-vent the film cracking on roll forming, etc. If thematerial has been stored outside at low temper-ature, a warm-up period should be allowed beforemanipulation of the sheet is undertaken.

The information on which this appendix is basedhas been kindly supplied mainly by the BritishSteel Corporation. More detailed informationmay be obtained from:

British Steel Corporation,Product Development Centre,Shotton Works,Deeside,Clwyd CH5 2NHTelephone: Chester (0244) 812345Telex: 61241

J.I Suitable gradesJ .1.1 Ductwork can be constructed from all thecommonly used aluminium alloys, the choicedepending on the purpose for which the ducts willbe used and the service environment.J.1.2 The alloys 1200, 3103 and 5251 (as specifiedin BS 1470) are easy to form and to join, and haveexcellent resistance to atmospheric corrosion, with5251 being rather more resistant to marineatmospheres.J .1.3 These alloys can be supplied in varioustempers produced by different degrees of cold roll-ing, so that a range of strengths is available. Inchoosing a temper, it is necessary to consider anyforming that will be done, as with the hardertempers the forming of tight bends might causecracking. Where high strength is required, alloy6082-TF sheet can be used.J.1.4 Aluminium strip is also available in the formof pre-painted coil.J.2 ConstructionJ.2.1 The general constructional requirements foraluminium ductwork are set out in Section 20.J.2.2 Where possible, aluminium bolts and rivetsshould be used. Stainless steel fasteners are alsosuitable, as are galvanized steel bolts as long as thezinc coating remains intact. Joints liable to entrapmoisture should be coated with a zinc chromateprimer before assembly.

J.2.3 All the aluminium alloys can be welded byMIG or TIG methods, with argon as the shieldinggas. Helium or a mixture of helium and argon canbe used, but not CO

2, Alloys in a work-hardened

temper are reduced to the annealed condition inthe heat affected zone; 6082-TF is reduced approx-imately from the TF to the TB temper. Alloys 1200and 3103 are easy to braze, as is 6082, but the latterneeds to be re-heat treated to regain its strength.J.3 Protective fmishesJ.3.1 In moist atmospheres, particularly if theyare contaminated by industrial effluent or by sanfrom the sea, surfaces not exposed to washing byrain will become roughened and covered with alayer of white corrosion product. However, thishas the effect of sealing the surface against furtherattack, and the mechanical properties of any butthe thinnest of materials will be only slightlyaffected.J .3.2 If the surface needs to be protected, any ofthe normal organic finishes can be used, includingthe laminated PVC films, although paints withheavy metal pigments are not suitable. The use ofpre-painted strip in coil form provides a reliablequality finish and often proves more economicalthan painting after assembly. Anodising providesan excellent finish for aluminium, but this processwould have to be carried out after forming andwould therefore not usually be practicable forductwork, except perhaps for ducts formed fromextrusions.

This appendix is based on material kindly suppliedby the Aluminium Federation Ltd., BroadwayHouse, Calthorpe Road, Five Ways, BirminghamB15 ITN (telephone: 021-4550311), from whommore detailed information may be obtained.

K.I GeneralReference is made in Section 6 and Appendix Aherein to EUROVENTand some explanation of thefunction. composition. objectives and member-ship of that body is therefore needed.K.2 MembershipEUROVEI'o'Tis an omnibus word standing for theEuropean Committee of the Construction of AirHandling Equipment. It was formed in 1959, andin 1977 its constituent members were the relevantnational associations in Austria, Belgium,Denmark. Finland, France, German FederalRepUblic. Italy. Netherlands. Norway, Sweden,SWItzerland and the United Kingdom.

K.3 ObjectivesThe objectives of EUROVENT are 'to improve anddevelop technical matters in the manufacture andoperation of air handling equipment; to improvethe professional status of its members and to facili-tate commercial exchanges between its membernations in the search for improved quality; and theadoption of rules, directives and codes of practicein the technical and economic spheres il1 themember countries'.K.4 UK representationMembership of EUROVENT is restricted to onebody in each of the countries listed in K.2 above. AsEUROVENT is largely concerned with the manu-

facture of equipment. the UK representative is theHEVAC Association. As regards ductwork. theDuct Work Group of HVCA during 1975 formallyaffiliated to the HEVAC Association. thus givingthe Group a direct voice in EUROVEr-.'Tductworkprojects.K.5 EUROVEI'l'T publicationsEUROVENT has published a number of docu-ments in the air handling field, and these includeDocument 2/3 covering the standardisation of ductsizes. Document 2/2 covers the procedure for test-ing for air leakage in ductwork, and provides fortwo levels of permissible. air leakage for low-pressure air distribution systems.K.6 EUROVENT Document 2/3 - standard sizesof ductsThis gives a range of standard sizes for both rectan-gular and circular ducts.As regards rectangular ducts, the Duct WorkGroup has adopted the EUROVENT recommenda-tions see Table 3 on page 13of this specification.As regards circular ducts, most of the spirally-wound circular ducts in the UK are made on form-ing heads based on Imperial measurements. It isnow common practice for these Imperial sizes tobe quoted in metric units, but the conversion is a

'soft' one, and thus in the larger diameters there is .a significant discrepancy between the nominalquoted dimensions and the actual ones. For thisreason, the nominal diameters of the circular ductshave been given separately in Table 13.K.' Possible ISO standard for duct sizesIn 1974EUROVENTproposed to the InternationalStandards Organisation (ISO) that the standardsizes specified in Document 2/3 be converted intoan International Standard.The ISO. as in duty bound, referred the proposal tothe various national standardising bodies - in thecase of the UK the British Standards Institution.At the time of preparing this ductwork specifi-cation, a representative committee of the aSI(including representatives of the HEVAC Associ-ation and of the Duct Work Group of HVCA) wasconsidering the matter.K.8 Air leakageThe basis on which air leakage is calculated inEUROVENT Document 2/2 has been adopted inDW/142, with the exception that the leakage limitsin Document 2/2 relate to the pressure classes A, Band C (see Section 6 of DW/142), while DW/142includes a limit for Class 0 - high-pressure duct-work up to 2500 Pa.

Infonnation about EUROVEr-.'T may be obtained from theHEVAC Association. Unit 3, Phoenix House, Phoenix Way,Heston, Middx. TW5 9ND (Telephone: 01-8972848)

Note - The extracts from BS 2989: 1982have beenprepared by the HVCA and are included here bycourtesy ofthe British Standards Institution.

L.I GENERALL.l.I The BS 2989: 1975 ('Hot-dip zinc coatedsteel sheet and coil') summarised in DW/141has been superseded by the 1982edition, whichis entitled 'Continuously hot-dip zinc coatedand iron-zinc alloy coated steel: wide strip,sheet/plate and slit wide strip'.L.l.2 Comparison of the following withAppendix D of DW/141 will show changes intype references.L.l.3 As before, the new British Standard setsout requirements for the conventional gal-vanized sheet and coil (and now also strip) andfor iron-zinc coated steel. (Both these are in-cluded in DW/142 - see Section 7.)The type of steel normally used for ductwork isZ2 G.2'S (under the previous British Standarddesignated as Z2, coating type C).

L.2 STEEL GRADESL.2.1 BS 2989: 1982lists the grades of steel set outin the next column, among others:

Grade Name of gradeZI Commercial

quality

Z2 Bending andprofiling quality

Z4 Special drawingquality

Z5 Special drawingquality, non-ageing

ApplicationForming quality steelsuitable for simplebending and formingoperationsForming quality steelsuitable for themanufacture of mostprofiles and moredifficult bendingoperationsForming quality steelsuitable for simpledrawing operationsand for more difficultprofiling operationsForming quality steelsuitable for deepdrawing and difficultforming operationsForming quality steelsuitable for deepdrawing and difficultforming operationswhere a non-ageingsteel is required

L.3 COATING TYPESL.3.1 The types of zinc coating are set out inTable 9 ofBS 2989: 1982 (reproduced at the footof this page).

LA SURFACE FINISHESL.4.1 BS 2989 includes a description of thevarious types of finish available:Normal spangle (N). A zinc coating finish,having a metallic lustre, that is the result ofunrestricted growth of the zinc crystals duringnormal solidification.NOTE. Normal spangle is the type normallysupplied for a wide variety of applications.Minimized spangle (M). A zinc coating finish,normally supplied with zinc coatings in therange G 100 to G350, that is obtained byrestricting the normal zinc crystal formation.Regular finish (R). The normal iron-zinc alloycoating finish; it is grey matt in appearance andshows no spangle.Smooth finish (S). A finish suitable fordecorative painting that is available for zinccoatings up to G350 and iron-zinc. alloycoatings.Extra smooth finish (XS). A coating finish,produced by rolling processes after coatingand available for zinc coatings up to G275and for iron-zinc alloy coatings, suitable forapplications where a high gloss painted finishis re.quired.

L.S SURFACE PROTECTIONL.S.I All types of coating normally receive asurface protection at the producer's plant.This may consist of chemical passivation; oroiling; or chemical passivation and oiling. Thepurchaser should state on his order thetreatment r~quired.

L.4.2 Chemical passivation and/or oilingprotects the surface against humidity andreduces the risk of formation of wet storagestains (so-called 'white rust'). However, theprotection afforded is limited. If the purchaserspecifies non-protected products, the manu-facturer is not responsible for the formation pfany storage stains. (Chemical passivation maycause slight discoloration of the surface that isnot detrimental to the general performance ofthe product.)

L.6 FORMINGL.6.1 The British Standard says that providedthat the profiling machine is set to avoid exces-sive stretching in the product, it is possible toform lock seams successfully with Z2 sheet up toa thickness of 1.5 mm and Z3 sheet up to 2 mm;and snap lock seams with Z2 up to 0.9 mm thicksheet and Z3 sheet up to 2 mm.

L.7 WELDINGL.7.1 Care should be taken to use propermethods and procedures. The iron-zinc coatingis more suitable for resistance welding than theconventional zinc coating.

Minimum coating mass

Coating designation(including both sides)

Triple SingleSuggested applications (see note 2)

spot test spot test

g/m2 g/m2

Zinc coatings (G) Light - for use where corrosion conditions areGI00 100 85G200 200 170 not severe and/or where forming

I operations preclude heavier coatings.

I G275 275 235 Standard

G350 350 300 Heavy duty - for longer life relative toG450 450 385G600 600 510 standard and light coatings.

Iron-zinc alloy coatings (IZ)IZIOO 100 85 Iron-zinc alloys - alloyed coatings of iron and zincIZ180 180 150

for easy painting and particularlyresistance welding.

Note 1. The mass of zinc is not always evenly divided between the two surfaces of the sheet. However, it cannormally be expected that not less than 40% of the specified minimum coating mass, as determinedby the single spot test, will be found on each surface.

Note 2.The suggested applications included in the right-hand column of the above table are those putforward by the British Steel Corporation.

APPENDIX M -·DESIGN NOTES FOR DUCTWORK'(CIBS Technical Memorandum No.8)

~t.l This manual brings together information onthe design of ductwork systems.~f.2 The contents have been drawn from the cur-rent relevant sections of the cms Guide and otherrecognised references, and include additionalmaterial on good design practice. The Notes makefrequent reference to DW/142, and an effort hasbeen made to ensure consistency between the twopublications. The Design Notes include chapterson:

Pressure loss in ducts. including corrections forduct surface type. air pressure, air density, tem-perature and altitude, and loss factors forfittings.Equivalent diameters of rectangular and flatoval ducts.Standard dimensions of circular, rectangularand flat oval ducts.

These notes have been contributed by theChartered Institution of Building Services, Delta

Included in this Bibliography are technical publications whichmay be of interest to ductwork designers. fabricators and erec-tors. and to those in the heating. ventilating. air conditioningindustries generally. Enquiries should be made of the relevantorganisation. at the address quoted.

HEATI~G AND \'ENTILATI~GCONTRACTORS' ASSOCIATION34 Palace Court, London W2 4JG Telephone:01- 229 2488; Telex:27929. Orders to HVCA Pub-lications, Old Mansion House, Eamont Bridge,Penrith. Cumbria CAlO 2BX (Telephone:0768 64771 Telex: 64326)DuctworkD\\'/141 Specification for sheet metal ductwork (low-.

medium- and high-pressure) (1982)D\\'/143 A practical guide to ductwork leakage testing

(1983)Other technical publicationsTR!5 Welding of carbon steel pipework (1980) - 'The

Grey Book'TR'3 Brazing and bronze welding of copper pipework

and sheet (1976) - 'The Copper Book'TR.6 Guide to Good Practice for Site Pressure Testing

of Pipework (1980)

CHARTERED I~STITUTIOS OF Bl'ILDINGSERVICESDelta House, 222Balham High Road;London SW12 9BS (Telephone: 01-6755211)

cms GuideVolume AVolumeBVolumeC

Design DataInstallation and Equipment DataReference Data

Commissioning CodesThese Codes cover the preliminary checks, setting to work andregulation of various categories of plant. The Codes give aguide to design implications.

Duct sizing methods, including velocity, equal-friction and static regain methods, and pressureloss calculations, with an example calculation.Heat loss from and gain to air in the duct; con-densation, noise control and fire.Commissioning and testing.Overseas work.Drawing symbols in current use.

M.3 The flow of heavilv contaminated air in ductsis not covered in detaii in the Notes; nor are theconstructional aspects of ductwork, which aredealt with in DW/142.M.4 The Notes are completed by references, abibliography of over thirty titles and appendicescovering properties of air, ductwork supportloads, velocity pressure for air flow and conversionto SI units.

House, 222 Balham High Road, London SW129BS (Telephone: 01-6755211)

Series A Air Distribution SystemsSeries B Boiler PlantSeries C Automatic Control SystemsSeries R Refrigerating SystemsSeries W Water Distribution SystemsTed1nlcal MemorandaNo. 1 Recommendations relating the design of air-

handling systems to fire and smoke control inbUildingsNotes on legislation relating to fire and servicesin buildingsNotes on legislation relating to the Health andSafety at Work etc. Act. 1974Design Notes for the Middle EastThe calculation and use of utilisation factorsLighting for Visual Display UnitsRecommendations on the use of small program-mable calculatorsDesign Notes for DuctworkNotes on Non-Statutory Codes and Standards.relating to Fire and Services in Buildings

Bl:ILDING SERVICES RESEARCH ANDINFORMATION ASSOCIATIONOld Bracknell Lane West, Bracknell, BerkshireRG124AH (Telephone: Bracknell (0344) 26511;Telex:848288 BSRIA C G)

No.4No.5No.6No. 7

No.8No. 9

Application GuidesAG.l/74 Designing Variable Volume Systems for Room

Air Movement

HEVAC ASSOCIATIONUnit 3, Phoenix House, Phoenix Way,Heston, Middx. TW5 9ND (Telephone:01-8972848)Fan Application Guide (Second Edition 1982)Guide to Air DiffusionGuide to Central,Station Air Handlrng UnitsGuide to Elimination of Noise in Fan Systems

El:ROVE:"IT publicatioM (enquiric to the HEVAC Assocation)1/1 Fan terminology2/1 Vocabulary relative to air diStribution and air

diffusionAir leakage rate in sheet metal air distributionsystemsSheet metal air ducts - standard for dimensionsManual for Regulating Air ConditioningInstallationsDocuments for Air System RegulationRoom Air Movement with Ceiling MountedDiffusers - Influence of Cold Windows

Glossary of terms relating to thermalinsulationSelf-tapping screws and metallic drive screwsGlossary of terms used in mechanised andhand sheet metal work and metal box makingPaint colours for building purposesHot rolled structural steel sections

Equal and unequal angles

Specification for the use of thermal insula-ting materialsCode of practice for mechanical ventilatingand air conditioning in buildingsCode of practice for thermal insulation ofpipework

BS4174:1972BS4342:1968

BS 4800:1972BS 4848:

Pan4:1972

BS S422:1977

2/3AG.lnS

AG.1I77AG.2nS

Laboratory ReportsLR.65 Air Movement in Rooms with Side-wall Mounted

GrillesLR.71 Air Movement in Rooms with Sill-Mounted

Grilles - Design ProcedureLR.75 Air Flow Generated Noise: Pan 1: Grilles and

DampersLR.78 Air Flow Generated Noise: Part 2: Bends with

Turning VanesLR.79 The Effect of Ceiling Beams and Light Fittings on

Ventilating JetsLR.80 Air Movement in Rooms with Ceiling Mounted

DiffusersLR.83 Air Movement in Rooms with Low Air Supply

Rates

SHEET METAL AND AIR CONDITIONINGCONTRACTORS' NATIONAL ASSOCIA-TION INC. (SMACNA)8224 Old Courthouse Road, Tyson's Corner,Vienna, Virginia 22180, U.S.A. (Telephone: 703-7909890)Architectural sheet metal manual (1979)Architectural sheet metal specifications (1980)Balancing and adjustment of air distribution (1967)Contractor's Handbook for Air Pollution ControlDuct liner application standards (197S)Fibrous glass duct construction standards (1979)Fire Damper and Heat Stop Guide (1981)Flexible Duct Performance and Installation Standard (1981)Guidelines for energy conservation in existing buildings (1974)Guidelines for energy conservation systems in new building(I97S)

Guidelines for Welding Sheet Metal (1977)High-pressure duct construction standards (1975)HVAC Duct Design Manual (1981)Industrial ventilation - manual for recommended practices

(1980)Low-velocity duct construction standards (1976)Rectangular Industrial Duct Construction Standard (1980)Round Industrial Duct Construction Standard (1977)Testing, balancing and adjusting of environmental systems

(1974)Thermoplastic duct (PVC) construction manual (1974)

BRITISH STANDARDS INSTITUTIONSales Department, 101Pentonville Road, LondonNI 9ND (Telephone: 01-8378801)DD 5:1971 Recommendations for metric plate and

sheet thickness and width/length combin-ations for metallic materialsRecommendations for methods of protec-tion against corrosion on light section steelused in buildingColours (of ready-mixed paints) for specificpurposesDucts for building servicesFire tests on buildingmaterials and structures

(Superseded by PartS)(Wirhdrawn)

External tire exposure roof testNon-combustibility test for materialsIgnitability test for materialsFire propagation test for materialsSurface spread of flame tests for materialsTest methods and criteria for the fireresistance of building construction

Hot dip galvanized coatings for iron andsteel articlesSteel plate. sheet and strip

Carbon steel plate. sheet and stripWroul!ht aluminium and aluminium allovsfor g;neral engineering purposes - plat~.sheet and stripWrought aluminium and aluminium anoys-bars. tubes and sectionsSprayed metal coatings

Protection of iron and steel by aluminiumand zinc against atmospheric corrosionProtection of iron and steel againstcorrosion and oxidation at elevatedtemperatures

Continuously hot-dip zinc coated and iron-zinc alloy coated steel

CP~13:1973BS ~76:

Part 1:1953

Part 3: 1975Part~: 1970Part 5: 1968Parr 6: 1968Part 7: 1971PartS: 197~

DEPARTMENT OF THE ENVIRONMENT(Property Services Agency)H.M. Stationery Office, 49 High Holborn,London WCIY 6HB (Telephone: 01-9281321) andbranchesM&ENo.11972M & E No.2 1968

Electrical installations in buildingsElectrical distribution systems external tobuildings

M & E No.3 1977 Heating, hot and cold water. steam andgas installations for buildings

M & E No.4 1970 Central heating and hot and cold waterinstallations for dwellings

M & E No.5 1969 Electrical installations in dwellings oftraditional construction

M & E No.6 1971 Mechanical ventilation for b~i1dings

TECHNICAL I~STRUCTIONS (M&E) MAINTENANCE4 Maintenance of Diesel Engines (1970)8 Planned Maintenance and Operation of

Mechanical and Electrical Services (1968)Inspection and Testing of ElectricalWiring Installations and Power Consum-ing Apparatus (1968)

Part 1:197:BS 1~70:197~

Sheet thicknessesEqui~'alents reproduced by courtesy of The M(,trication Board

Galvanized steel

Standard Birminghamthickness Gauge

inch mm BG inch.0197 0.5 26 .0196.0236 0.6 24 .0248.0~76 0.7.0315 0.8 22 .0312.0354 0.9.0394 1.0 20 .0392.0472 1.2

18 .0495.0630 1.6 16 .0625.0787 2.0 14 .0785.0984 2.5 12 .0991

O.S mm is a standard thickness for galvanizedsheet only

2.S mm is a standard thickness for hot-rolled" sheet only

Aluminium ,Standard Standard ~thickness Wire Gauge

inch mm swg inch26 .018

.0197 0.524 .022

;0236 0.6.0276 0.7 22 .028.0315 0.8.0354 0.9 20 .036.0394 1.0.0472 1.2 18 .048.0630 1.6 16 .064.0787 2.0 14 .080.0984 2.5

12 .104.1181 3.0

10 .128

To com'ertLengthInches to millimt:tresFeet to metres

25.400.3048

AreaSquare inches to square millimetresSquare feet to square metres

645.20.0929

Millimetres to inchesMetres to feet

0.039373.281

Square millimetres to square inchesSquare metres to square feet

0.0015510.764

VolumeCubic feet to cubic metresCubic feet to litresGallons (U K) to litres

0.0283228.314.546

Cubic metres to cubic feetLitres to cubic feetLitres to gallons (U K)

35.3150.0353

0.22

MassOunces to gramsPounds to kilogramsTons to tonnes

28.350.4536

1.016

Grams to ouncesKilograms to poundsTonnes to tons

0.035272.205

0.9842

Volume flowCubic feet per minute to cubic

metres per secondCubic feet per minute to litres

per second

0.000472

0.4719

MotioDFeet per minute to metres per second

PressureInches water gauge to millibarsInches water gauge to pascals (Pa)1 Pa = I Newton per square metre -:

2.491249.1

10-2 millibars

Cubic metres per second to cubicfeet per minute

Litres per second to cubic feetper minute

2119

2.119

Standard dimensions of steeland aluminium sheet

Steel(black and galvanised)

Metric Equivalent

mm it/in2000 x 1000 6' 63/~"- x 3' 33/8"2500 x 1250 8' 27h6" x 4' 11/~"3000 x 1350 9' 101Is" x 4' 511s"3000 x 1500* 9' 101/s" x 4' llllt6"

Aluminium(commercially pure and alloy)

Metric Equivalent

mm ftfin2000 x 1000 6' 6i" x 3' 3,"2500 x 1250 8' 2..-1.-"x 4' 1*"3750 x 1250* 12' 3 i" x 4' IF

Weigh' perThickness square I//£"re

mm kg0.5 3.9213

'2.45 - 0.6 4.70560.7 5.4898

2.Z~;~ 0.8 6.27410.9 7.0584

2..;)<.- 1.0 7.8426(.~: A 1.2 9.4111\.;"S· 1.6 12.5481

2.0 15.68522.5 19.6064

The figure in the central column can be read aseither the metric or the British measure. Forexample. 1 millimetre = 0.03937 inch; or 1 inch ,;"25.4 millimetres.

0.794 *1.587 -to3.175 *4.763 *6.350 !7.938 k9.525 ,

11.112 710

12.700 !14.290 ik15.876 t17.462 1/;-19.050 i20.636 ~~22.222 7.-23.809 *25.4 1 0.0393750.8 2 0.0787476.2 3 0.11811

101.6 4 0.15748127.0 5 0.19685152.4 6 0.23622177.8 7 0.27559203.2 8 0.31496228.6 9 0.35433254.0 10 0.39370279.4 II 0.43307304.8 12 0.47244330.2 13 0.51181355.6 14 0.55118381.0 15 0.59055406.4 16 0.62992431.8 17 0.66929457.2 18 0.70866482.6 19 0.74803508.0 20 0.78740635.0 25 0.98425762.0 30 1.18110889.0 35 1.37795

1016 40 1.574801143 45 1.771651270 50 1.968501397 55 2.165351524 60 2.362201651 65 2.559051778 70 2.755901905 75 2.952752032 80 3.149602159 85 3.346452286 90 3.543302413 95 3.740152540 100 3.93703810 150 5.90555080 200 7.87406350 250 9.84257620 300 11.81108890 350 13.7795

10160 400 . 15.748011430 450 17.716512700 500 ••. 19.68515240 600 23.62217780 700 27.55920320 800 31.49622860 900 35.43325400 1000 39.370