ABC Del Esprayado Devilbiss

ABCs of Spray Finishing

ABCs of Spray Finishing$10.00 1-239-C

11/01

While this book examines the spray finishing operation and itsequipment from many viewpoints,there is still much more to belearned to become truly proficientat spray finishing.

The best way to become proficientat spray finishing is to just do it!Many trade technical andcommunity colleges offer coursesin spray finishing, a great way toimprove your skills.

Many of the tricks of theprofessional spray finisher involvepaints and coatings. Themanufacturers of these materialsroutinely publish complete bookson these subjects. Thesepublications are available inspecialty paint stores and willprovide you with considerabledetail. Many of these books alsocontain information on techniquesfor surface preparation.

Another important source ofinformation, particularly onequipment use and selection isyour local spray finishingequipment distributor. No bookcould ever completely cover aspecialists in-depth knowledge ofequipment, techniques,maintenance and troubleshooting.

Information is available from manyresources on the subject of sprayfinishing. It is our hope that thisbook will provide you with a starttoward perfecting your finishingskills.

A recent addition to resourcesavailable to the spray finisher is the World Wide Web. Manymanufactures are represented andquestion and answer forums areavailable. Please visit our websiteat www.devilbiss.com.

About this book.....

This book has been updatedseveral times from The ABCs ofSpray Equipment, originallypublished by The DeVilbissCompany in 1954. It focuses onequipment and techniques forspray finishing.

The format of the original book wasquestion-and-answer. We haveretained that format in this edition.

This book is organized around themajor components of an air spraysystem spray guns, materialcontainers, hose, air controlequipment, compressors, spraybooths, respirators and a shortsection on general cleanliness andother sources of information. Athorough understanding of thematerial in this book - plus a lot ofactual spray painting practice -should enable you to handle justabout any spray painting situation.

Although we have made an effortto make this book as detailed andas complete as possible, be awarethat the equipment and productsystems used to illustrate pointsare entirely based on DeVilbisstechnology. DeVilbiss is the worldsoldest and largest manufacturer ofspray painting equipment, and hasmaintained this leadership since itsfounding in 1888.

Forward..........................................2

1. Introduction..............................3

Surface Preparation..................3

Paint Preparation ......................3

2. Air Atomizing Spray Guns ......4

Spray Gun Types ......................4

Part Identification and Function.....................................6

Operation...................................9

Maintenance ...........................11

Troubleshooting ......................13

3. Material Containers ..............16

4. Hose and Connections.........18

5. Air Control Equipment ..........20

6. Respirators.............................22

7. Air Compressors ...................23

8. Spray Booths .........................25

Forward Table of Contents

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This book is about the selection,use and maintenance of finishingequipment: spray guns, tanks,cups, hoses, compressors,regulators, spray booths,respirators, etc. It presumes thatyou are familiar with standardsurface preparation techniques thatmay be required before finishingactually begins. It also presumes abasic knowledge of the manydifferent types of paints andcoatings available.

Creating a perfect finish requires asolid knowledge of surfacepreparation, finishes and spraypainting equipment. The first twoare extensively covered in manyother books. The manufacturers ofpaints and coatings have gone togreat length to publish informationon their new and existing products.

But, even an extensive knowledgeof surface preparation techniquesand paint chemistry is not enoughto assure a professional finish. Thefinish must be applied by a spraygun, and all the variables of its usemust be mastered.

The equipment necessary to applythe finish the spray gun, tank,cup, regulator, hoses, compressor,etc. must all be matched to thejob as well as to each other. Thatequipment must be used andmaintained properly, with anappreciation of how and why itworks the way it does.

The moment of truth for any finishhappens when the trigger is pulled.This book focuses on that moment.

Surface Preparation

The surface to be finished shouldbe well cleaned before painting. Ifthe paint manufacturersinstructions call for it, the surfaceshould be chemically treated. Usea blow-off gun and tack rag toremove all dust and dirt. Noamount of primer or paint will coverup a badly prepared surface.

Plastic parts may contain staticelectricity from the moldingprocess. This static attractsparticles of dust and dirt. Eliminatethem by treating with destatisiz-ing air using a special blow-offgun that imparts a neutral chargeto the airflow. A chemical anti-statictreatment is also available.

Paint Preparation

Todays finishes are extremelycomplex chemical formulations.They include both solvent andwaterborne types. Some mayrequire the addition of solvents toform the proper spraying viscosity.Others may simply require theaddition of a second component ata prescribed ratio to obtainsprayable consistency. Many ofthem also have hardeners or otherchemicals, added to them to insurecorrect color match, gloss,hardness, drying time or othercharacteristics necessary toproduce a first class finish. Makesure you are familiar with thespecific finish material data sheetsaccompanying each material. Donot mix materials from variousmanufacturers. Read and followdirections carefully.

All finish materials must also besupplied with a Material SafetyData Sheet (MSDS). This dataprovides information on properhandling and disposal of materials.Many states require that MSDS bekept on file by the user.

The first step is knowing the typeand color of paint the projectrequires. With this determined,follow the manufacturersinstruction for preparing it exactly.If you have any doubts about howto proceed, dont guess! Contactyour paint supplier for help.Improperly prepared paint willnever produce a good finish!

The chief characteristic thatdetermines the sprayablility of paint

and how much film may be appliedis its viscosityor consistency.Following the paint manufacturersinstructions will get you close, butfor professional results, use aviscosity cup. It is a simple but veryaccurate way to measure thethickness of paint. With the cup,you can thin or reduce the paint tothe precise consistency required bythe manufacturer.

Always prepare paint in a clean,dust-free environment. Paint has aremarkable ability to pick up dirt.Dirty paint will not only clog yourspray gun, but it will also ruin yourpaint job. Get in the habit of alwayspouring paint into the cup or tankthrough a paint strainer. Paint isnever as clean as it looks.

1. Introduction

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Introduction

The spray gun is the keycomponent in a finishing system. Itis a precision engineered andmanufactured instrument. Eachtype and size is specificallydesigned to perform a certain,defined range of tasks.

As in most other areas of finishingwork, having the right tool for thejob goes a long way toward get-ting professional results.

This chapter will help you knowwhich is the proper gun by review-ing the Conventional Air and HighVolume/Low Pressure spray gundesigns commonly used in finish-ing suction feed, gravity feed andpressure feed. It will also review thedifferent types of guns andcomponents within each design.

A thorough understanding of thedifferences between systems willallow you to select the right gun, touse it properly to produce a highquality finish and to contributetoward a profitable finishingoperation.

SPRAY GUN TYPES

1. What is an air spray gun?

An air spray gun is a tool which uses compressed air to atomizepaint, or other sprayable material,and to apply it to a surface.

Air and material enter the gunthrough separate passages and aremixed at the air cap in a controlledpattern.

2. What are the types of air sprayguns?

Air spray guns may be classified invarious ways. One way is by thelocation of the material container:

Figure 1 shows a gun with a cupattached below it.

Figure 3 shows a gun with a cupattached above it.

Figure 4 shows a material containersome distance away from itspressure feed gun.

The type of material feed system isalso a way of classifying guns:

Suction Feed...draws material tothe gun by suction as in Figure 1.

Gravity Feed...the material travelsdown, carried by its own weightand gravity as in Figure 3.

Pressure Feed...the material is fedby positive pressure as in Figure 4.

Guns may also be classified aseither external or internal mixdepending upon the type of aircap.

3. What is a suction feed gun?

A spray gun design in which astream of compressed air creates avacuum at the air cap, providing asiphoning action. Atmosphericpressure on the material in the suc-tion cup forces it up the suctiontube, into the gun and out the fluidtip, where it is atomized by the aircap. The vent holes in the cup lidmust be open. This type gun isusually limited to a one-quart, orsmaller, capacity container and lowto medium viscosity materials.

Figure 1- Suction Feed Gun withattached cup

Suction feed is easily identified by the fluid tip extending slightlybeyond the face of the air cap, see figure 2.

Figure 2 - Suction Feed Air Cap

Suction feed guns are suited tomany color changes and to smallamounts of material, such as intouchup or lower productionoperations.

4. What is a gravity feed gun?

This design uses gravity to flow thematerial from the cup, which ismounted above the gun, into thegun for spraying. No fluid pick-uptube is used, since the fluid outletis at the bottom of the cup.

This cup has a vent hole at the topof the cup that must remain open.It is limited to 32 ounce capacitiesdue to weight and balance.

Gravity feed guns are ideal forsmall applications such as spot repair, detail finishing or for finish-ing in a limited space. They requireless air than a suction feed gun,and usually have less overspray.

Figure 3 - Gravity Feed Gun withattached cup

2. Air Atomizing Spray Guns

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5. What is a pressure feed gun?

In this design, the fluid tip is flushwith the face of the air cap (seeFigure 5). The material ispressurized in a separate cup, tankor pump. The pressure forces thematerial through the fluid tip and tothe air cap for atomization.

Figure 4 - Typical Pressure FeedGun with remote pot

This system is normally used whenlarge quantities of material are tobe applied, when the material istoo heavy to be siphoned from acontainer or when fast applicationis required. Production spraying ina manufacturing plant is a typicaluse of a pressure feed system.

Figure 5 - Pressure Feed Air Cap

Table 1

6. What is an external mix aircap?

This gun mixes and atomizes airand fluid outside the air cap.

It can be used for applying alltypes of materials, and it isparticularly desirable whenspraying fast drying paints such as lacquer. It is also used when ahigh quality finish is desired.

Figure 6 - External Mix Gun

7. What is an internal mix cap?

This cap mixes air and materialinside the air cap, before expellingthem.

It is normally used where low airpressures and volumes areavailable, or where slow-dryingmaterials are being sprayed.

A typical example is spraying flatwall paint, or outside house paint,with a small compressor.

Internal mix caps are rarely usedfor finishing when a fast-dryingmaterial is being sprayed, or whena high quality finish is required.

Figure 7 - Internal Mix Air Cap

8. What is HVLP?

HVLP, or High-Volume/LowPressure, uses a high volume of air(typically between 10-26 CFM)delivered at low pressure (10 PSI orless at the air cap) to atomize paintinto a soft, low-velocity pattern ofparticles.

In many cases, less than 10 psi isneeded in order to atomize.

Proper setup utilizes no more fluidand air pressure than is needed toproduce the required quality and aflow rate that will meet productionrequirements.

As a result, far less material is lostin overspray, bounceback andblowback than with conventionalair spray. This is why HVLP deliversa dramatically higher transferefficiency (the amount of paint thatadheres to the substrate comparedto the amount of paint sprayed)than spray systems using a higheratomizing pressure.

The HVLP spray gun resembles astandard spray gun in shape andoperation. Models that use highinlet pressure (20-80 psi) andconvert to low pressure internallywithin the spray gun are calledHVLP conversion guns.

Some HVLP models, particularlythose using turbines to generateair, bleed air continuously tominimize back-pressure against the air flow of the turbine.

The air cap design is similar to thatof a standard spray gun, with avariety of air jets directing theatomizing air into the fluid stream,atomizing it as it leaves the tip.

HVLP is growing in popularity andnew environmental regulations arerequiring it for many applications.

HVLP can be used with a widevariety of materials, including two-component paints, urethanes,acrylics, epoxies, enamels,lacquers, stains, primers, etc.

2. Air Atomizing Spray Guns (Contd)

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A DeVilbiss Pro Tip:When using a gravity feed system,downsize the tip one size from suction.If the suction system calls for a .070",use a .055" or .063"

Type Viscosity Fluid Atomizing TypeFeed (#2 Zahn) Oz/Minute Pressure Production

Suction up to 24 10-12 40-50 Low

Gravity up to 24 10-12 30-50 Low

Pressure up to 29 30-Oct 50-60 High

HVLP up to 29 14-16 10 High

PART IDENTIFICATIONFUNCTION

9. What are the principal parts ofa spray gun?

Figure 8 - Spray Gun Anatomy

10. What happens when thetrigger is pulled?

The trigger operates in two stages.Initial trigger movement opens theair valve, allowing air to flowthrough the gun.

Further movement of the triggerpulls the fluid needle from its seatat the fluid tip, allowing fluidmaterial to flow. When the trigger isreleased, the fluid flow stops beforethe air flow.

This lead/lag time in the triggeroperation assures a full spraypattern when the fluid flow starts. It also assures a full pattern untilthe fluid flow stops, so there is nocoarse atomization.

11. What is the function of the air cap?

The air cap (see figure 10) directscompressed air into the fluidstream to atomize it and form thespray pattern. (see Figure 9)

Round Tapered Blunt

Figure 9 - Types of Spray Patterns

There are various styles of caps toproduce different sizes and shapesof patterns for many applications.

12. What are the advantages ofthe multiple jet cap?

This cap design provides betteratomization of more viscousmaterials.

It allows higher atomizationpressures to be used on moreviscous materials with less dangerof split spray pattern.

It provides greater uniformity inpattern due to better equalizationof air volume and pressure from thecap.

It also provides better atomizationfor materials that can be sprayedwith lower pressures.

Figure 10 - Multiple Jet External MixAir Cap

13. How should an air cap beselected?

The following factors must be considered:

a) type, viscosity and volume ofmaterial to be sprayed

b) size and nature of object, orsurface to be sprayed (multiple, orlarger, orifices increase ability toatomize more material for fasterpainting of large objects).

Fewer, or smaller orifices usuallyrequire less air, produce smallerspray patterns and deliver lessmaterial. (These caps are designedfor painting smaller objects and/orusing slower speeds)

c) material feed system used(pressure, suction or gravity)

d) size of fluid tip to be used (mostair caps work best with certain fluidtip/needle combinations)

e) volume of air in cubic feet perminute (cfm) and pressure inpounds per square inch (psi) available.

See the DeVilbiss spray guncatalog for proper selection of air cap / fluid tip / needlecombinations and typical uses.

14. What is the function of thefluid tip and needle?

They restrict and direct the flow ofmaterial from the gun into the airstream. The fluid tip includes aninternal seat for the tapered fluidneedle, which reduces the flow ofmaterial as it closes. (see Figure 11).

The amount of material that leavesthe front of the gun depends uponthe viscosity of the material, thematerial fluid pressure and the sizeof the fluid tip opening providedwhen the needle is unseated fromthe tip.

Fluid tips are available in a varietyof sizes to properly handlematerials of various types, flowrates and viscosity.

Figure 11 - The Fluid Tip andNeedle


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15. What is the nozzlecombination?

In practice, the air cap, fluid tip,needle and baffle are selected as aunit, since they all work together toproduce the quality of the spraypattern and finish. These fouritems, as a unit, are referred to asthe nozzle combination.

16. What are standard fluid tipsizes and flow rates?

The standard sizes, correspondingfluid tip opening dimensions andflow rates are:

Conventional Air Spray

Table 2

HVLP

Table 3

17. How are fluid tip and needlesizes identified?

DeVilbiss fluid tips and needles areidentified by the letters stamped onthe tip and the needle.

The identification letters on thesecomponents should match. Seethe appropriate DeVilbiss spray guncatalog for the proper selection offluid tip and needle combinations.

18. What fluid tip and needlecombination sizes are mostcommon?

E, EX, FF and FX are mostgenerally used. The EXcombination is used for suctionfeed, while FF and FW are used forgravity Feed. For pressure feed themost common tips are FX, FF and E.

19. How are nozzle combinationsselected?

Five basic considerations areinvolved in selecting the nozzlecom-bination:

type and viscosity of materialbeing sprayed

physical size of object beingfinished/fan pattern size

desired speed/finish quality

gun model being used

available air volume (cfm) andpressure (psi) from compressor

(1) The type and viscosity of thematerial being sprayed is thefirst factor to consider.

Table 4

NOTE: Viscosity conversion chartsare available to convert oneviscosity cup reading to anotherfrom any material or equipmentsupplier.

(2) The physical size of the objectto be painted must also beconsidered. As a general rule, usethe largest possible spray patternconsistent with the object size.Remember that different air capsdeliver various pattern characteris-tics. This can reduce both sprayingtime and the number of gunpasses.

(3) The next consideration inevaluating nozzle combinations isthe speed with which the finish willbe applied and the desired level ofquality.

For speed and coverage, choose anozzle combination whichproduces a pattern as wide aspossible.

When quality is the deciding factor,choose a nozzle combinationwhich produces fine atomizationand a smaller pattern size, therebygiving greater application control.

(4) The model of the gun itself willlimit the selection of nozzlecombination.

For a DeVilbiss suction feed gun,there are several nozzle typesavailable which are suitable forfinishing operations. These nozzles


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Tip ID Flow Rate

Pressure Feed Systems

G .028"/.7mm up to 12 oz/min

FX .0425"/1.1mm up to 20 oz/min

FF .055"/1.4mm up to 30 oz/min

E .070"/1.8mm over 30 oz/min

EE .070"/1.8mm porcelain enamel

D .086"/2.2mm heavy body mtls

AC .110"/2.75mm heavy body mtls

Suction Feed Systems

EX .070"/1.8mm up to 12 oz/min

FW .062"/1.6mm up to 10 oz/min

Gravity Feed Systems



Tip ID Flow Rate

Pressure Feed Systems

FX .0425"/1.1mm up to 10 oz/min


E .070"/1.8mm up to 20 oz/min

D .086"/2.2mm over 20 oz/min

Suction Feed Systems

D .086"/2.2mm up to 9 oz/min

DE .070"/1.8mm up to 8 oz/min

Gravity Feed Systems



Rule of thumb

Optimum fluid pressures are 8-20psi. Pressures greater than thisgenerally indicate the need for alarger fluid tip size.

Rule of thumb

The lower the viscosity of thematerial, the smaller the I.D. ofthe fluid tip.

Material Production TipViscosity Rate Size#2 Zahn

up to 23 sec Low FX(.042)23-28 sec Med FF(.055)28-48 sec High E(.070)over 48 sec High D(.086)

have fluid tip openings rangingfrom .062" to.086", and aredesigned to handle viscosities upto 28 seconds in a No. 2 ZahnViscosity Cup.

For a DeVilbiss pressure feed gun,the amount of material dischargeddepends upon material viscosity,inside diameter of the fluid tip,length and size of hose, andpressure on the material containeror pump.

If the fluid tip opening is too small,the paint stream velocity will be toohigh. If the fluid tip opening is toolarge, you will lose control over thematerial discharging from the gun.

For most HVLP guns, the paintflow shouldn't exceed 16 oz. perminute. For higher flow rates,consult the DeVilbiss HVLP SprayGun catalog.

(5) Available air supply is the lastfactor to consider.

Pressure feed air caps consumebetween 7.0 and 25.0 CFM,depending on design. If your airsupply is limited, because of anundersize compressor, or manyother air tools are in use at once,the gun will be starved for air,producing incomplete atomizationand a poor finish.

20. What are the criteria forselecting a pressure feed nozzle?

While the fluid discharge in ouncesper minute from a suction feed gunis relatively stable (largely becauseit is determined by atmosphericpressure), the fluid discharge froma pressure feed gun depends moreupon the size of the insidediameter of the fluid tip and thepressure on the paint container orpump. The larger the opening, themore fluid is discharged at a givenpressure.

If the fluid tip ID is too small for theamount of material flowing from thegun, the discharge velocity will betoo high. The air, coming from the

air cap, will not be able to atomizeit properly causing a center-heavypattern.

If the fluid tip opening is too large,material discharge control will be lost.

The fluid tip/air cap combinationmust be matched to each otherand to the job at hand. Spray guncatalogs include charts to help you match them properly.

21. Of what metals are fluid tipsmade?

Tips are made of the followingmetals:

a) 300-400 grade stainless steel forboth non-corrosive and corrosivematerials

c) Carboloy inserts for extremelyabrasive materials

22. What is viscosity?

The viscosity of a liquid is its body,or thickness, and it is a measure of its internal resistance to flow.Viscosity varies with the type andtemperature of the liquid. Anyreference to a specific viscositymeasurement must beaccompanied by a correspondingtemperature specification.

The most common measurementused to determine viscosity infinishing is flow rate (measured inseconds from a Zahn, Ford, Fisheror other viscosity cup).

Different viscosity cup sizes areavailable. Each cup has a hole atthe bottom, specified to an exactsize. Use a viscosity cup that isdesigned to handle the time rangeof the materials in use. Viscositycontrol is an extremely importantand effective method to maintainapplication efficiency and qualityconsistency. Always measureviscosity after each batch ofmaterial is mixed and make surematerial temperature is the same,normally 70 to 80 F.

Viscosity recommendations may be given in poise and centipoise (1 poise=100 centipoise). Viscosityconversion may be accomplishedby consulting a viscosityconversion chart.

23. What is the spreader adjust-ment valve?

A valve for controlling the air to thehorn holes which regulate the spraypattern from maximum width downto a narrow or round pattern (see figure 8).

24. What is the fluid needleadjustment?

This adjustment controls thedistance the fluid needle is allowedto retract from its seat in the fluidtip, which allows more or lessmaterial through the fluid tip (see figure 14).

With pressure feed systems, thefluid delivery rate should beadjusted by varying the fluidpressure at the pressure pot. Usethe fluid adjustment knob for minorand/or temporary flow control. Thiswill extend the life of the fluidneedle and tip.

25. What are the components ofsuction and gravity feedsystems?

Typical suction and gravity feedsystems consist of: a suction feedor gravity feed spray gun with cup,an air compressor (not shown), acombination filter/air regulator andair hoses (see figure 12).


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Figure 12 Suction Feed andGravity Feed System Components

OPERATION

26. How is suction and gravityfeed equipment hooked up foroperation?

Connect the air supply from thecompressor outlet to the filter/airregulator inlet.

Connect the air supply hose fromthe air regulator outlet to the airinlet on the spray gun.

After the material has beenreduced to proper consistency,thoroughly mixed and strained intothe cup, attach the gun to the cup(suction feed) or pour material intoattached cup (gravity feed).

27. How are suction and gravityfeed systems initially adjusted forspraying?

(1) Spray a horizontal test pattern(air cap horns in a vertical position).Hold the trigger open until the paintbegins to run. There should berelatively even distribution of thepaint across the full width of thepattern. (see Figure 13). Adjust thepattern width with the spreaderadjustment valve. If distribution isnot even, there is a problem witheither the air cap or the fluid tipthat must be corrected. Refer to

the Troubleshooting Section forexamples of faulty patterns to helpdiagnose your problem.

Figure 13 - Horizontal Test Pattern

(2) If the pattern produced by theabove test appears normal, rotatethe air cap back to a normalspraying position and begin spray-ing. (Example - a normal patternwith a #30 air cap will be about 9"long when the gun is held 8" fromthe surface).

Figure 14 Fluid Adjustment Screw

(3) With the fluid adjusting screwopen to the first thread,(see figure14) and the air pressure set atapproximately 30 psi, make a testpass (move the spray gun 3 timesthe normal speed) with the gun onsome clean paper, cardboard orwood. If there are variations inparticle size- specks and/or largeglobs - the paint is not atomizingproperly (see figure 15).

(4) If the paint is not atomizingproperly, increase the air pressureslightly and make another testpass. Continue this sequence untilthe paint particle size is relativelyuniform.

Uneven Distribution

Even Distribution

Figure 15- Test Patterns

(5) If the pattern seems starved formaterial, and the fluid adjustmentscrew allows full needle travel, thefluid tip may be too small or themater-ial may be too heavy.Recheck the viscosity or increasethe size of the fluid tip and needle

(6) If the material is spraying tooheavily and sagging, reduce thematerial flow by turning in the fluidadjusting screw (clockwise).

Remember, proper setup utilizes nomore fluid and air pressure than isneeded to produce the requiredquality and a flow rate that willmeet production requirements.


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28. What are the components ofa pressure feed system?

A pressure feed system consists of:a pressure feed spray gun, a pres-sure feed tank, cup or pump, an airfilter/regulator, appropriate air andfluid hoses, and an air com-pressor(see figure 16).

Figure 16 - Pressure Feed SystemComponents

29. How is equipment hooked upfor pressure feed spraying?

Connect the air hose from the airregulator to the air inlet on the gun.

Connect the mainline air hose tothe air inlet on the tank. CAUTION:Do not exceed the container'smaximum working pressure.

Connect the fluid hose from thefluid outlet on the tank to the fluidinlet on the gun.

30. How is the pressure feed gunadjusted for spraying?

Open spreader adjustment valvefor maximum pattern size (seefigure 8).

Open fluid adjustment screw untilthe first thread is visible (see figure 14).

31. How is the pressure feed gun balanced for spraying?

1) Using control knob on fluidregulator, set fluid pressure at 5 to 10 psi.

2) Using control knob on airregulator, set air atomizationpressure at 25-35 psi.

3) Spray a test pattern (fast pass)on a piece of paper, cardboard, orwood. From that test pattern,determine if the particle size issmall enough and relatively uniformthroughout the pattern to achievethe required finish quality (seefigure 15). If particle size is toolarge or is giving too much texturein the finish, turn the atomizationpressure up in 3 to 5 psiincrements until particle size andtexture of finish is acceptable.

4) Spray a part with these settings.If you are not able to keep up withthe production rate required or ifthe finish is starved for material,increase the fluid pressure with thefluid regulator control knob in 2 to4 psi increments until required wetcoverage is accomplished. Note: A larger capacity fluid tipmay be required.

5) Remember, as you turn up thefluid pressure the particle size willincrease. Once the coveragerequired is obtained, it will benecessary to re-adjust theatomization pressure in 3 to 5 psiincrements as explained in step 3to insure required particle size andfinish texture is achieved.

6) If using HVLP, using an Air CapTest Kit, verify that the air cappressure in not above 10 psi ifrequired by a regulatory agency.

Figure 17 Air Cap Test Kit

After establishing the operatingpressures required for productionand finish quality, develop aPressure Standardization programfor your finish room to follow.

32. What is a PressureStandardization Program?

After establishing air and fluidpressures that meet required qual-ity and production, record the datato be used for that application forfuture reference. (see figure 18)

Figure 18 PressureStandardization Chart

33. How should the spray gun beheld?

It should be held so the pattern isperpendicular to the surface at alltimes.

Keep the gun tip 8-10 inches (airspray guns) or 6-8 inches (HVLPguns) from the surface beingsprayed.


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Booth #: _______________

Material Sprayed ________

Application _____________

Viscosity _______________

Fluid Temperature ________

Spray Gun ______________

Air Cap ______ Fluid Tip ___

Air Pressure _____________

Fluid Pressure ____________

34. What is the proper techniquefor spray gun stroke andtriggering?

The stroke is made with a free armmotion, keeping the gun at a rightangle to the surface at all points ofthe stroke.

Triggering should begin just beforethe edge of the surface to besprayed. The trigger should be heldfully depressed, and the gunmoved in one continuous motion,until the other edge of the object isreached. The trigger is thenreleased, shutting off the fluid flow,but the motion is continued for afew inches until it is reversed forthe return stroke.

When the edge of the sprayedobject is reached on the returnstroke, the trigger is again fullydepressed and the motioncontinued across the object.

Lap each stroke 50% over thepreceding one. Less than 50%overlap will result in streaks on thefinished surface. Move the gun at aconstant speed while the trigger ispulled, since the material flows at aconstant rate.

Another technique of triggering isreferred to as feathering.Feathering allows the operator tolimit fluid flow by applying onlypartial trigger travel.

35. What happens when the gunis arced?

Arcing the stroke results in unevenapplication and excessive over-spray at each end of the stroke.When the tip is arced at an angle of45 degrees from the surface (seefigure 19), approximately 65% ofthe sprayed material is lost.

Figure 19 - Spray Techniques

36. What is the proper sprayingsequence and technique forfinishing applications?

Difficult areas, such as corners andedges, should be sprayed first. Aimdirectly at the area so that half ofthe spray covers each side of theedge or corner.

Hold the gun an inch or two closerthan normal, or screw the spreaderadjustment control in a few turns.Needle travel should be only partialby utilizing the featheringtechnique. Either technique willreduce the pattern size.

If the gun is just held closer, thestroke will have to be faster tocompensate for a normal amountof material being applied to smallerareas.

When spraying a curved surface,keep the gun at a right angle tothat surface at all times. Follow the curve. While not alwaysphysically possible, this is the idealtechnique to produce a better,more uniform, finish.

After the edges, flanges andcorners have been sprayed, the

flat, or nearly flat, surfaces shouldbe sprayed.

Remember to overlap thepreviously sprayed areas by 50%to avoid streaking.

When painting very narrowsurfaces, you can switch to asmaller gun, or cap with a smallerspray pattern, to avoid readjustingthe full size gun. The smaller gunsare usually easier to handle inrestricted areas.

A full size gun could be used,however, by reducing the air pressure and fluid delivery andtrigger-ing properly.

MAINTENANCE

37. How should the air cap becleaned?

Remove the air cap from the gunand immerse it in clean solvent. Ifnecessary, use a bristle brush toclean dried paint. Blow it dry withcompressed air.

If the small holes become clogged,soak the cap in clean solvent. Ifreaming the holes is necessary, usea toothpick, a broom straw, orsome other soft implement (seefigure 20).

Cleaning holes with a wire, a nail ora similar hard object couldpermanently damage the cap byenlarging the jets, resulting in adefective spray pattern.

Figure 20 - Cleaning the Air Cap


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38. How should guns be cleaned?

A suction or pressure feed gun withattached cup should be cleaned asfollows:

Turn off the air to the gun, loosenthe cup cover and remove the fluidtube from the paint. Holding thetube over the cup, pull the triggerto allow the paint to drain back intothe cup.

Empty the cup and wash it withclean solvent and a clean cloth. Fillit halfway with clean solvent andspray it through the gun to flushout the fluid passages by directingstream into an approved, closedcontainer. All containers used totransfer flammable materials shouldbe grounded. (Be sure to complywith local codes regarding solventdisposal).

Then, remove the air cap, clean it as previously explained, and replace it on the gun.

Wipe off the gun with a solvent-soaked rag, or if necessary, brushthe air cap and gun with a fiberbrush using clean-up liquid or thinner.

To clean a pressure feed gun withremote cup or tank, turn off airsup-ply to cup or tank. Releasemateri-al pressure from the systemby opening relief valve.

Material in hoses may be blownback. The lid must be loose andfluid pressure off. Keep gun higherthan container, loosen air cap andtrigger gun until atomizing airforces all material back into thepressure vessel.

A gun cleaner may be used foreither type of gun. This is anenclosed box-like structure (vented) with an array of cleaningnozzles inside.

Guns and cups are placed over thenozzles, the lid is closed, the valveis energized, and the pneumaticallycontrolled solvent sprays throughthe nozzles to clean the equipment.

The solvent is contained, and mustbe disposed of properly.

Some states codes require the useof a gun cleaner, and it is un-lawfulto discharge solvent into theatmosphere.

After cleaning a spray gun in a guncleaner, be sure to lubricate asindicated in Figure 22.

Figure 21 - Using a Hose Cleaner

Use a hose cleaner to cleaninternal passages of spray gunsand fluid hose. This deviceincorporates a highly efficient fluidheader, which meters a precisesolvent/air mixture. The cleaneroperates with compressed air andsends a finely - atomized blast ofsolvent through the fluid passagesof the hose, the spray gun, etc.

This simple, easy to use cleanerspeeds up equipment cleaning andsaves solvent. Savings may be asmuch as 80%. It also reduces VOCemissions. (Be sure that both thehose cleaner and gun areproperly grounded.)

Where local codes prohibit the useof a hose cleaner, manuallybackflush the hose into the cup ortank with solvent until clean anddry with compressed air.

Clean the container and add cleansolvent. Atomization air should beturned off during this procedure.Pressurize the system and run the solvent through until clean. (Be sure to comply with localcodes regarding solvent dispersionand disposal.)

Clean the air cap, fluid tip and tank.Reassemble for future use.

39. What parts of the gun requirelubrication? (Figure 22)

The fluid needle packing A, the airvalve packing B and the triggerbearing screw C require dailylubrication with a non-silicone/non-petroleum gun lube.

The fluid needle spring D should be coated lightly with petroleumjelly or a non-silicone grease (ie. Lithium).

Lubricate each of these points afterevery cleaning in a gun washer!

Figure 22 - Lubrication Points


12

1. Packing nut loose2. Packing worn or dry

1. Sticking air valve stem2. Foreign matter on air valve

or seat3. Worn or damaged air valve

or seat 4. Broken air valve spring5. Bent valve stem6. Air valve gasket damaged

or missing

1. Dry packing2. Packing nut too tight3. Fluid tip or needle worn

or damaged4. Foreign matter in tip5. Fluid needle spring broken6. Wrong size needle or tip

All Feed Systems1. Loose or damaged fluid

tip/seat2. Dry packing or loose fluid

needle packing nut3. Material level too low4. Container tipped too far5. Obstruction in fluid passage6. Loose or broken fluid tube

or fluid inlet nipple

Suction Feed Only7. Material too heavy8. Air vent clogged9. Loose, damaged or dirty lid

10. Fluid tube resting on cup bottom

11. Damaged gasket behind fluid tip

1. Tighten, do not bind needle2. Replace or lubricate

1. Lubricate2. Clean

3. Replace

4. Replace5. Replace6. Replace

1. Lubricate2. Adjust3. Replace tip and needle with

lapped set4. Clean5. Replace6. Replace

1. Tighten or replace2. Lubricate packing or tighten

packing nut3. Refill4. Hold more upright5. Backflush with solvent

6. Tighten or replace

7. Thin or reduce8. Clear vent passage9. Tighten, replace or clean

coupling nut10. Tighten or shorten

11. Replace gasket


13

Fluid leaking from packing nut

Air leaking from front of gun

Fluid leaking or dripping fromfront of pressure feed gun

Jerky, fluttering spray

Problem Cause Correction

Top or bottom-heavy spraypattern*

Right or left-heavy spraypattern*

Center-heavy spray pattern

Split spray pattern


14

1. Horn holes plugged

2. Obstruction on top or bottomof fluid tip

3. Cap and/or tip seat dirty

1. Horn holes plugged

2. Dirt on left or right side of fluid tip

1. Fluid pressure too high for atomization air (pressure feed)

2. Material flow exceeds air caps capacity

3. Spreader adjustment valve set too low

4. Atomizing pressure too low5. Material too thick

1. Fluid adjusting knob turned in too far

2. Atomization air pressure too high

3. Fluid pressure too low (pressure feed)

4. Fluid tip too small

1. Clean, ream with non-metallicpoint (ie. toothpick)

2. Clean

3. Clean

1. Clean, ream with non-metallicpoint (ie. toothpick)

2. Clean

1. Balance air and fluid pressureIncrease spray pattern width

2. Thin or reduce fluid flow

3. Adjust

4. Increase pressure5. Thin to proper consistency

1. Back out counter-clockwise toincrease flow

2. Reduce at regulator

3. Increase fluid pressure

4. Change to larger tip


*Remedies for the top, bottom,right, left heavy patterns are:1. Determine if the obstruction is on

the air cap or fluid tip. Do this bymaking a solid test spray pattern.Then, rotate the cap one-half turnand spray another pattern. If thedefect is inverted, obstruction is onthe air cap. Clean the air cap aspreviously instructed.

2. If the defect is not inverted, it is onthe fluid tip. Check for a fine burron the edge of the fluid tip.Remove with #600 wet or dry sandpaper.

3. Check for dried paint just inside theopening. Remove paint by washingwith solvent.


15

1. Inadequate material flow

2. Low atomization air pressure(suction feed)

1. Fan adjustment stem not seating properly

1. Air pressure too high2. Material not properly reduced

(suction feed)3. Gun too far from surface4. Gun motion too fast

1. Too much atomization air pressure

2. Gun too far from surface3. Improper technique (arcing,

gun speed too fast)

1. Too much, or too fast-drying thinner

2. Too much atomization air pressure

1. Pressure feed cap/tip used with suction feed

2. No pressure at gun3. Fluid needle not retracting4. Fluid too heavy (suction feed)

1. Back fluid adjusting screw out to first thread or increasefluid pressure

2. Increase air pressure and rebalance gun

1. Clean or replace

1. Lower air pressure2. Reduce to proper consistency

and temperature3. Adjust to proper distance4. Slow down

1. Reduce pressure

2. Use proper gun distance3. Use moderate pace, keeping

gun parallel to work surface

1. Remix with proper reducer and temperature

2. Reduce pressure

1. Use suction feed cap/tip

2. Check air lines3. Open fluid adjusting screw4. Lower fluid viscosity or

change to pressure feed

Starved spray pattern

Unable to form round spray pattern

Dry spray

Excessive overspray

Excessive fog

Will not spray


Introduction

All spray painting systems - fromthe smallest brush to the mostsophisticated finishing system-must have containers to hold thematerial being applied.

Material container types and sizesvary considerably, depending onthe kind of spraying system beingused.

This chapter will discuss thesecontainers, their particular applica-tions, their construction andmaintenance.

1. What are material containers?

Any container which serves as amaterial supply reservoir for thespray gun. These containers areusually made of metal or plasticwith capacities of 1/2 pint or more.

2. What are the types of materialcontainers?

There are three common types ofcups which attach to the gun itself:Siphon, Gravity and Pressure.

There are also remote pressurecups and tanks, which are locatedaway from the gun. See Page 4 fortypes of guns and systems.

3. Where are cup containersused?

Cup containers are typically onequart or less, and are used whererelatively small quantities of material are being sprayed.

4. How are material feed cupsattached to lid assemblies?

Cups are attached using a lidassembly (sometimes called a cupattachment) that either clamps A orscrews B onto the cup container.(see Figure 1) Some lid assembliesare detachable from the gun, whileothers are integral parts and do notdetach from less expensive models.

A B

Figure 1 - Cup Attachment Styles

5. What capacity does a pressurefeed cup have?

A pressure feed cup can have aone or two quart capacity.

Anything larger is considered apressure feed tank, which may bepositioned some distance from thegun.

Figure 2 - Regulated 2 Qt. PressureCup

6. How do pressure feed tankswork?

Pressure feed tanks are closedcontainers, ranging in size fromabout two gallons to 60 gallons.They provide a constant flow ofmaterial, under constant pressure,to the spray gun.

The tank is pressurized with clean,regulated, compressed air, whichforces the fluid out of the tankthrough the fluid hose to the gun.

The rate of fluid flow is controlledby increasing or decreasing the airpressure in the tank.

A typical pressure feed tankconsists of: the shell A, clamp-onlid B, fluid tube C, fluid outlet D,regulator E, gauge F, safety reliefvalve G, and agitator H (see figure 3).

Pressure feed tanks are availablewith either top or bottom fluidoutlets, and with variousaccessories.

Figure 3 - Pressure Feed Tank

7. Where are pressure feed tanksrecommended?

Pressure feed tanks provide apractical, economical method offeeding material to the gun overextended periods of time.

They are mostly used in continuousproduction situations, because thematerial flow is positive, uniformand constant.

Tanks can be equipped withagitators (see Figure 3) that keepthe material mixed and insuspension.

3. Material Containers

16

8. When is an agitator used in apressure feed tank?

When the material being used hasfiller or pigment that must be keptin motion to keep its particles inproper suspension. An agitator canbe hand, air or electrically driven.

9. What is a single regulatedtank?

This is a pressure feed tank withone air regulator controlling onlythe pressure on the material in thetank (see figure 4).

Figure 4 - Single Regulated Tank

10. What is a double regulatedtank?

This is a pressure feed tankequipped with two air regulators(see figure 5).

One provides regulation for the airpressure on the material in the tank(thereby controlling fluid flow). Theother controls atomization airpressure to the spray gun.

Figure 5 - Double Regulated Tank

11. What are code and non-codepressure tanks?

Code tanks are manufactured torigid standards as specified by theAmerican Society of MechanicalEngineers. (ASME) Each step ofmanufacture is closely controlled,and welding of the shell is certified.Code tanks are designed towithstand pressures up to 110 psi.

Non-code tanks are normallyrestricted to 3 gallons in size orless. Due to the type ofconstruction, non-code tanks arerated at 80 psi or less. Regulationsmay restrict the type of materialsand pressures used with a non-code pressure tank.

12. What materials are used toconstruct pressure feed tanks?

The smaller, non-code, light-dutytanks are made of plated steel andhave lower inlet pressurerestrictions.

The heavy-duty, ASME-code tanksare made of galvanized or 300series stainless steel. They alsohave plated or stainless steel lidswith forged steel clamps.

When abrasive or corrosivematerials are being sprayed, thetank shell is coated or lined with aspecial material, or a containerinsert is used.

13. What are container liners?

They are inserts that are placedinside the tank to hold the material,keeping it from direct contact withthe tank walls. They are made ofdisposable polyethylene.

Using liners reduces tank cleaningtime and makes color changeovereasier.

14. When would you use abottom outlet tank?

1) When you are using very viscousmaterials.

2) When continuous, steadypressure is required, such as whenfeeding plural componentproportioning equipment.

3) When you wish to use all thematerial in the tank and you are notusing an insert.

15. What would I use if I havedifficulty accurately setting lowerfluid pressures?

An extra-sensitive regulator isavailable for use with lower fluidflow and/or lower viscositymaterials where precise control isneeded.

3. Material Containers (Contd)

17

Introduction

The various types of hose used tocarry compressed air and fluidmaterial to the spray gun areimportant parts of the system.Improperly selected or maintainedhose can create a number ofproblems. This chapter will reviewthe different kinds of hose andfittings in use, provide guidance inselecting the proper types for thejob and cover the maintenance ofhose.

1. What types of hose are used inspray painting?

There are two types: air hose used to transfer compressed airfrom the air source to the gun, andfluid hose used only in pressurefeed systems to transfer thematerial from its container to thespray gun.

(NOTE: Do not use air hose forsolvent-based materials.)

Figure 1 - Basic Hose Construction

2. How is hose constructed?

DeVilbiss hose is a performancedesigned combination of threecom-ponents: Tube A,Reinforcement B and Cover C.

The tube is the interior flexibleartery that carries air or fluidmaterial from one end of the hoseto the other.

The reinforcement adds strength tothe hose. It is located between thetube and cover, and it can be manycombinations of materials andreinforcement design. Its designdetermines pressure rating,flexibility, kink and stretchresistance and coupling retention.

The cover is the outer skin of thehose. It protects the reinforcementfrom contact with oils, moisture,solvents and abrasive objects. Thecover protects the reinforcement,but does not contribute to hoseperformance.

3. What type of tube is used influid hose?

Since the solvents in coatingswould readily attack and destroyordinary rubber compounds, fluidhose is lined with special solvent-resistant nylon material that isimpervious to common solvents.

4. What sizes of fluid hose arerecommended?

Figure 2 - Recommended fluid hosesizes

5. What sizes of air hose arerecommended?

The hose from the regulator to agun or tank should be a minimumof 5/16" ID. Tools requiring more airmay need 3/8" I.D. hose or larger.

Figure 3 - Recommended air hose sizes

6. What is pressure drop?

This is the loss of air pressure dueto friction (caused by air flow)between the source of the air andthe point of use. As the air travelsthrough the hose or pipe, it rubsagainst the walls. It loses energy,pressure and volume as it goes.

7. How can this pressure drop bedetermined?

At low pressure, with short lengthsof hose, pressure drop is notparticularly significant. As pressureincreases, and hose is lengthened,the pressure rapidly drops andmust be adjusted.

All air hose is subject to pressureloss or drop. For example, 1/4"pressure drop is 1 psi per foot and5/16" is 1/2 psi per foot. Thispressure loss may result in pooratomization.

Too often, a tool is blamed formalfunctioning, when the realcause is an inadequate supply ofcompressed air due to anundersized I.D. hose.

4. Hoses & Connections

18

RED or TAN ...........air and water

GREY............air w/static ground

BLACK ..........low pressure fluid

DeVilbiss hose is color-coded:

Type Length Size

General 0' - 20' 1/4" ID

Purpose 10' - 35' 3/8" ID

35' - 100' 1/2" ID

100' - 200' 3/4" ID

Type Length Size

0' - 10' 1/4" ID

General 10' - 20' 5/16" ID

Purpose 20' - 50' 3/8" ID

50' - 100' 1/2" ID

0' to 20' 5/16" ID

HVLP 20' - 50' 3/8" ID

50' - 100' 1/2" ID

For optimum spray gun results, the following is recommended: up to 20 ft - 5/16" I.D., over 20 ft - 3/8" I.D.

8. How are hoses maintained?

Hoses will last a long time if theyare properly maintained.

Be careful when dragging hoseacross the floor. It should never be pulled around sharp objects, run over by vehicles, kinked orotherwise abused. Hose thatruptures in the middle of a job can ruin or delay the work.

Proper hose cleaning techniquesare covered on Pages 11 and 12.

The outside of both air and fluidhose should be occasionally wipeddown with solvent. At the end ofevery job, they should be stored by hanging up in coils.

9. What kinds of hose fittings areavailable?

Permanent, crimp type or reusablefittings are used to connect hosesto air sources or to sprayequipment.

10. What kinds of hoseconnections are available?

Although there are many differentstyles, the two most common arethe threaded and the quick-disconnect types.

Remember that elements added toany hose, such as elbows,connectors, extra lengths of hose,etc., will cause a pressure drop.

On HVLP systems, quick-disconnects must have larger,ported openings (high flow) todeliver proper pressure foratomization. Because of normalpressure drop in these devices,most are not recommended for usewith HVLP.

11. What is a threaded- typeconnection?

This is a common swivel-fittingtype that is tightened with awrench.(see figure 4).

Figure 4 - Threaded-TypeConnection

12. What is a quick-disconnecttype connection?

This is a spring-loaded, male/ female connection systemthat readily attaches and detachesby hand. No tools are required (see figure 5).

Figure 5 - Quick-Disconnect TypeConnection

Care should be taken whenselecting a quick-disconnect airconnection. Due to design, mostQ.D. connections result insignificant pressure drop. This canadversely affect spray guns withhigher consumption air caps suchas HVLP.

4. Hoses & Connections (Contd)

19

Introduction

The control of volume, pressureand cleanliness of the air entering aspray gun are of critical importanceto the performance of the system.

Following some key installationprinciples will help decrease therisk of contaminants. For example,its important to use the right sizeair compressor for your application.An overworked air compressor canproduce a significant amount of dirtand oil. Additionally, proper pipingis very important to help preventcondensation from forming withinthe line and contaminating the airsupply.

This chapter examines the varioustypes of equipment available toperform these control functions.

1. What is air control equipment?

Any piece of equipment installedbetween the air source and thepoint of use that modifies thenature of the air.

2. Why is air control equipmentnecessary?

Raw air, piped directly from an airsource to a spray gun, is of littleuse in spray finishing. Raw aircontains small, but harmful,quantities of water, oil, dirt andother contaminants that will alterthe quality of the sprayed finish.Raw air will likely vary in pressureand volume during the job.

There will probably be a need formultiple compressed air outlets torun various pieces of equipment.

Any device, installed in the air line,which performs one or more ofthese functions, is considered tobe air control equipment.

3. What are the types of aircontrol equipment?

Air control equipment comes in awide variety of types, but itbasically all performs one or moreof the following functions; airfiltering/cleaning, air pressureregulation/indication and airdistribution through multipleoutlets.

4. How does an air filter work?

It filters out water, oil, dust and dirtbefore they get on your paint job.Air entering the filter is swirled toremove moisture that collects inthe baffled quiet zone.

Smaller impurities are filtered outby a filter. Accumulated liquid iscarried away through either amanual or automatic drain.

Figure 1 - Air Filter

5. What is an air regulator?

This is a device for reducing themain line air pressure as it comesfrom the compressor. Once set, itmaintains the required air pressurewith minimum fluctuations.

Regulators are used in lines alreadyequipped with an air filtrationdevice.

Air regulators are available in awide range of cfm and psicapacities, with and withoutpressure gauges and in differentdegrees of sensitivity and accuracy.

They have main line air inlets andregulated or non-regulated airoutlets.

6. How is an air filter/regulatorinstalled?

Bolt the air filter/regulator Asecurely to the spray booth wallnear the operator. (see Figure 2)

This location makes it convenientto read the gauges and operate thevalves. Install the filter/regulator atleast 25 feet from the Bcompressed air source. Install theC takeoff elbow on top of the Dmain air supply line.

Piping should slope back towardthe compressor, and a E drain legshould be installed at the end ofeach branch, to drain moisturefrom the main air line.

Use piping of sufficient I.D. for thevolume of air being passed, andthe length of pipe being used.

Table 1

5. Air Control Equipment

20

Minimum Pipe Size Recommendations*

Compressor Main Air Line

HP CFM LENGTH SIZE

1 1/2-2 6-9 Over 50' 3/4"

3-5 12-20 Up to 200' 3/4"

Over 200' 1"

5-10 20-40 Up to 100' 3/4"

100' - 200' 1"

Over 200' 1 1/4"

10-15 40-60 Up to 100' 1"

100' - 200' 1 1/4"

Over 200' 1 1/2"

*Piping should be as direct aspossible. If a large number offittings are used, larger I.D. pipeshould be installed to helpovercome excessive pressure drop.

Figure 2 Air/Filter RegulatorInstallation

7. How often should thefilter/regulator be drained ofaccumulated moisture and dirt?

It depends largely on the level ofsystem use, the type of filtration inthe air system, and the amount ofhumidity in the air.

For average use, once-a-daydrainage is probably sufficient.

For heavily-used systems, or inhigh humidity, drainage shouldoccur several times daily.

Some units drain automaticallywhen moisture reaches apredetermined level.

8. What steps should be taken ifmoisture passes through thefilter/regulator?

Since moisture in the spray gunatomization air will ruin a paint job,it must be removed from the airsupply.

When the compressed airtemperature is above its dew pointtemperature, oil and water vaporwill not condense out into solidparticles.

Check the following:

a) Drain transformer, air receiverand air line of accumulatedmoisture.

b) Be sure the transformer islocated at least 25 feet from the air source.

c) Main air line should not runadjacent to steam or hot waterpiping.

d) Compressor air intake shouldnot be located near steamoutlets or other moisture-producing areas.

e) Outlet on the air receiver shouldbe near the top of the tank.

f) Check for damaged cylinderhead or leaking head gasket, ifthe air compressor is watercooled.

g) Intake air should be as cool aspossible.

9. What causes excessive pres-sure drop on the main line gaugeof the filter/regulator?

a) The compressor is too small to deliver the required air volume and pressure for alltools in use.

b) The compressor is not functioning properly.

c) There is leakage in the air line or fittings.

d) Valves are partially opened.

e) The air line, or piping system,is too small for the volume of air required. Refer to Table 1,Page 20.

5. Air Control Equipment (Contd)

21

Introduction

Consult with appropriate safetypersonnel or Industrial Hygienistif in doubt as to the suitability of aparticular respirator before using it.Respirators may not provideprotection against eye and skinabsorption of chemicals.

Spray finishing creates a certainamount of overspray, hazardousvapors and toxic fumes. This istrue, even under ideal conditions.

Anyone near a spray finishingoperation should use some type ofrespirator, or breathing apparatus.This chapter covers various typesof equipment for this use.

1. What is a respirator?

A respirator is a mask that is wornover the mouth and nose toprevent the inhalation of oversprayfumes and vapor.

2. Why is a respirator necessary?

For two reasons:

First...some type of respiratoryprotection is required by OSHA/NIOSH regulations.

Second...even if it wasn't a require-ment, common sense tells you thatinhaling overspray is not healthy.

Overspray contains toxic particlesof paint pigments, harmful dustand, in some cases, vapor fumeswhich can be harmful to yourhealth.

Depending on design, a respiratorcan remove some, or all, of thesedangerous elements from the airaround a spray finishing operator.

3. What types of respirators areused by spray finishingoperators?

There are three primary types; theair-supplied respirator, the organicvapor respirator and the dustrespirator.

4. What is an air-suppliedrespirator?

This type is available in both maskand visor/hood styles. Both providethe necessary respiratoryprotection when using materialsthat are not suitable for organicvapor respirators.

The visor/hood style provides agreater degree of coverage to thehead and neck of the operator.

Both styles require a positivesupply of clean, breathable air asdefined by OSHA (Grade D).

Figure 1 Positive PressureVisor/Hood

Figure 2 Positive Pressure MaskRespirator

5. What is an organic vaporrespirator and where is it used?

This type of respirator, whichcovers the nose and mouth, (see Figure 3) is equipped withreplaceable cartridges that removeorganic vapors by chemicalabsorption.

Some are designed with pre-filtersto remove solid particles from the

air before it passes through thechemical cartridge.

The organic vapor respirator isnormally used in finishingoperations with standard materials(not suited for paints containingisocyanates).

Figure 3 - Organic Vapor Respirator

6. What is a dust respirator andwhere is it used?

Dust respirators are sometimesused in spray finishing but, in most applications, they areunsatisfactory. (see Figure 4)

Figure 4 - Dust Respirator

These respirators are equippedwith cartridges that remove onlysolid particles from the air. Theyhave no ability to remove vapors.

They are effective, however, inpreliminary operations such assanding, grinding and buffing.

NOTE:

Before using any respirator,carefully read the manufacturersSafety Precautions, Warnings andInstructions. Many respirators arenot suitable for use withisocyanates, asbestos, ammonia,pesticides, etc.

6. Respirators

22

Introduction

All air tools, spray guns, sanders,etc., must be supplied with airwhich is elevated to higherpressures and delivered insufficient volume. The aircompressor compresses air for use in this equipment and is amajor component of a spraypainting system. This chapter will examine the various typesavailable.

Compressed air is measured onthe basis of volume supplied perunit of time (cubic feet per minute,or cfm) at a given pressure persquare inch (psi), referred to asdelivery.

Displacement is the output of air by a compressor at zero pressure,or free air delivery.

1. What is an air compressor?

An air compressor is a machinedesigned to raise the pressure ofair from normal atmosphericpressure to some higher pressure,as measured in pounds per squareinch (psi). While normalatmospheric pressure is about 14.7 pounds per square inch, acompressor will typically deliver airat pressures up to 200 psi.

When selecting a compressor:

Rule of thumb

The cubic feet per minute deliveredby an electrically powered 2 stageindustrial air compressor is 4 timesthe motor's horse power rating.(CFM=4xHP)

2. What types of compressors aremost common in spray finishingoperations?

There are two common types; thepiston-type design and the rotaryscrew design.

Because most commercial sprayfinishing operations consume largequantities of compressed air at

relatively high pressures, the pistontype compressor is the morecommonly used.

3. How does a piston-typecompressor work?

This design elevates air pressurethrough the action of areciprocating piston. As the pistonmoves down, air is drawn inthrough an intake valve. As thepiston travels upward, that air iscompressed. Then, the now-compressed air is dischargedthrough an exhaust valve into theair tank or regulator.

Piston type compressors areavailable with single or multiplecylinders in one or two-stagemodels, depending on the volumeand pressure required.

Figure 1 - Piston Type AirCompressor

4. How does a rotary screwcompressor work?

Rotary screw compressors utilizetwo intermeshing helical rotors in atwin bore case. Air is compressedbetween one convex and oneconcave rotor. Trapped volume ofair is decreased and the pressure isincreased.

Figure 2 Rotary Screw AirCompressor

5. What is a single stagecompressor?

This is a piston-type compressorwith one or more cylinders, inwhich air is drawn from theatmosphere and compressed to itsfinal pressure with a single stroke.

All pistons are the same size, andthey can produce up to 125 psi.

6. Where are single stagecompressors used?

The application of this compressoris usually limited to a maximumpressure of 125 psi. It can be usedabove 125 psi, but above thispressure, two stage compressorsare more efficient.

7. What is a two-stagecompressor?

A compressor with two or morecylinders of unequal size in whichair is compressed in two separatesteps.

The first (the largest) cylindercompresses the air to an intermediate pressure. It thenexhausts it into a connecting tubecalled an intercooler.

From there, the intermediatepressurized air enters the smallercylinder, is compressed even moreand is delivered to a storage tankor to the main air line.

Two-stage compressors can deliverair to over 175 psi.

They are normally found inoperations requiring compressedair of 125 psi or greater.

8. What are the benefits of two-stage compressors?

Two-stage compressors are usuallymore efficient. They run cooler anddeliver more air for the powerconsumed, particularly in the over-100 psi pressure range.

7. Air Compressors

23

9. Is there anything else to know,about air compressors?

Because this book mainly focuseson spray guns, it provides onlybasic coverage of air compressorsand how they operate.

There is much more to know:

How to select the properequipment in terms of size,delivery, etc.

Compressors may be portable orstationary and there are differentmodels to meet a variety of needs.

7. Air Compressors (Contd)

24

Introduction

Containing the overspray andkeeping it out of the air and offother objects is an importantconsideration in a spray finishingoperation. This chapter discussesvarious types of booths and detailsperiodic maintenance.

1. What is a spray booth?

A compartment, room or enclosureof fireproof construction; built toconfine and exhaust overspray andfumes from the operator andfinishing system.

There are various models available,designed for particular sprayapplications. Spray booths may bepartially enclosed (figures 1 & 2) ortotally enclosed (figure 3).

Consult the National Fire ProtectionAssociation (NFPA) pamphlet #33and the O.S.H.A. requirements forconstruction specifications.

2. What are the benefits of aspray booth?

A well-designed and maintainedspray booth provides importantadvantages:

It separates the spraying operationfrom other shop activities, makingthe spraying, as well as the otheroperations, cleaner and safer.

It reduces fire and health hazardsby containing the overspray.

It provides an area that containsresidue, making it easier to keepclean. It also keeps both theoperator and the object beingsprayed cleaner.

In a booth equipped with adequateand approved lighting, it providesbetter control of the finish quality.

3. What types of spray booths arethere?

There are two; the dry filter typeand the waterwash type.

4. What is a dry filter type spraybooth?

This booth draws overspray-contaminated air throughreplaceable filters and vents thefiltered air to the outside.

It is the most common type ofbooth for most industrial andautomotive applications.

It is used for spraying low-volume,slower-drying materials, and is notaffected by color changes.

Figure 1 - Dry Filter Type Booth

5. What is a waterwash typebooth?

A waterwash booth actuallywashes the contaminatedoverspray air with a cascade ofwater and traps the paint solids.Fewer paint particles reach theoutside atmosphere to harm theenvironment.

Waterwash booths are generallyused when spraying high volumesof paint.

Figure 2 - Waterwash IndustrialType Spray Booth

Figure 3 Automotive DowndraftDry Filter Booth

6. What is an exhaust fan?

A typical exhaust fan consists of amotor, a multiple blade fan, pulleysand belts. It removes oversprayfrom the spray booth area (see figure 4).

Contemporary exhaust fans arecarefully designed to preventoverspray from coming into contactwith the drive mechanism.

Blades are made of non-sparkingmetal, and they move themaximum volume of air-per-horsepower against resistancesuch as exhaust stacks, filters, etc.(See NFPA pamphlet #33.)

8. Spray Booths

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Figure 4 Exhaust fan

7. What is air velocity?

Air velocity in a finishing operationis the term used to describe thespeed of air moving through theempty spray booth.

8. What effect does air velocityhave on spray booth efficiency?

Air must move through the boothwith sufficient velocity to carryaway overspray.

Too low a velocity causes poor,even potentially dangerous workingconditions, especially when thematerial contains toxic elements. Italso increases maintenance costs.

Too high a velocity wastes powerand the energy required to heatmake-up air.

9. What is a manometer?

It is a draft gauge that indicateswhen paint arrestor filters or intakefilters are overloaded. (see figure 5)

Some states and local codesrequire a manometer gauge oneach bank of filters to comply withOSHA regulations.

Figure 5 - Manometer

10. What does an air replacementunit do?

The volume of air exhausted from aspray booth is often equal to threeor more complete air changes perhour.

Under such conditions, thetemperature may become irregularand uncomfortable. Excessive dustmay become a problem.

To prevent these conditions,sufficient make-up air must beintroduced to compensate for theexhausted air.

The air replacement unitautomatically supplies thismakeup air - both filtered andheated - to eliminate the problemsof air deficiency and airbornecontaminants.

Figure 6 - Air Replacement Unit

11. What routine maintenancedoes a dry type spray boothrequire?

(a) The continuous flow of air through the booth eventuallyloads the filters with dirt andoverspray. Periodically, inspectand replacethem with

multi-stage filters, designed forspray booth use. Single-stagefurnace filters will not do the job.

(b) Monitor the manometerreading daily, and know what a normal reading should be.

(c) Keep the booth free of dirt andoverspray. Floors and wallsshould be wiped down afterevery job. Pick up scrap,newspapers, rags, etc.

(d) Coat the inside of the boothwith a strippable, spray-oncovering. When the oversprayon it becomes too thick, stripand recoat.

(e) Periodically check the lightinginside the booth, and replaceweak or burned out bulbs.Improper lighting can causethe operator to apply a poorfinish.

12. What routine maintenancedoes a waterwash type boothrequire?

(a) Compounding of the water inthis type unit is essential.Employ only booth treatmentchemicals in accordance withsuppliers recommendations.The ph of the water should bebetween 8 and 9.

(b) Maintain the water level at the proper setting per manufacturers specifications.

(c) Check the tank for paintbuildup on the bottom, checkthe pump strainer to keep itclean and clear, check the airwasher chamber and thenozzles in the header pipe. If the nozzles are plugged, the overspray will encroach on thewash baffle section, fan and stack.

(d) Periodically check the float valve for proper operation. Flood the sheet to be sure there is a uniform flow over the entire surface.

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(e) Keep the booth interior and exhaust stack free from overspray and dirt accumulation.

13. What checks can be used toassure good results from a spraybooth?

(a) Keep the interior of the booth clean.

(b) Maintain and replace intake and exhaust filters when necessary.

(c) Caulk all seams and crackswhere dirt might enter.

(d) Maintain and clean all equipment used in the booth.

(e) Keep operators clothing clean and lint-free.

(f) Perform routine maintenance above on a scheduled basis.

8. Spray Booths (Contd)

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NOTES

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NOTES

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1-239-C 2001, ITW Industrial Finishing All rights reserved Printed in U.S.A.

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