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ITable of contentsContents1.1 The history of compressed air ............................................... 11.1.1 The origin of compressed air ................................................ 11.1.2 The first applications of compressed air ............................... 21.2 Units and formula symbols .................................................... 61.2.1 Basic units ............................................................................ 61.2.2 Compressed air units ........................................................... 61.3 What is compressed air ? ....................................................... 71.3.1 The composition of air .......................................................... 71.3.2 The properties of compressed air ........................................ 71.3.3 How does compressed air behave? ..................................... 71.4 Physical fundamentals ........................................................... 81.4.1 Temperature ......................................................................... 91.4.2 Volume ................................................................................. 91.4.3 Pressure............................................................................. 101.4.4 Volume flow........................................................................ 111.5 Compressed air in motion .................................................... 131.5.1 Flow behaviour ................................................................... 131.5.2 Types of flow ...................................................................... 132.1 The advantages of compressed air ..................................... 142.2 Pressure ranges .................................................................... 172.3 Possible applications for compressed air ........................... 182.3.1 Tensioning and clamping with compressed air ................... 182.3.2 Conveyance by compressed air ......................................... 182.3.3 Pneumatic drive systems ................................................... 192.3.4 Spraying with compressed air ............................................ 192.3.5 Blowing and flushing with compressed air .......................... 192.3.6 Testing and inspection with compressed air ....................... 202.3.7 Using compressed air for process control .......................... 202.4 Examples of specialised applications ................................. 213.1 Compressors (compactors) .................................................. 243.1.1 Dynamic compressors ( Turbo-compressors ) .................... 243.1.2 Displacement compressors ................................................ 243.2 Types of compressor ............................................................ 253.2.1 Standard compressors ....................................................... 263.2.2 Piston (reciprocating) compressor ...................................... 273.2.3 Diaphragm compressor ...................................................... 293.2.4 Free piston compressor ...................................................... 303.2.5 Rotary vane compressor .................................................... 313.2.6 Liquid ring compressor ....................................................... 323.2.7 Screw compressor ............................................................. 333.2.8 Roots compressor .............................................................. 343.2.9 Axial compressor ................................................................ 353.2.10 Radial compressor ............................................................. 36Part 1Fundamentals ofcompressed airPart 2Applications forpneumaticsPart 3Compressed airgeneratorsChapter PageIITable of contentsPart 4Control of compressorsChapter Page3.3 Piston compressors .............................................................. 373.3.1 General .............................................................................. 373.3.2 Suction capacity - output .................................................... 383.3.3 Cooling ............................................................................... 393.3.4 Coolant ............................................................................... 403.3.5 Control of reciprocating piston compressors ...................... 403.3.6 Advantages of reciprocating piston compressors ............... 403.3.7 Components of a piston compressor .................................. 413.4 Screw compressors .............................................................. 423.4.1 General .............................................................................. 423.4.2 Compression process ........................................................ 423.4.3 Method of operation ........................................................... 433.4.4 Oil circuit ............................................................................ 443.4.5 Pneumatic circuit ................................................................ 453.4.6 Heat reclamation ................................................................ 463.4.7 Intake control ...................................................................... 463.4.8 Advantages of screw compressors..................................... 463.4.9 Main components of a screw compressor .......................... 473.5 Components .......................................................................... 483.5.1 Drive motor ......................................................................... 483.5.2 Drive belts .......................................................................... 483.5.3 Belt tensioning.................................................................... 483.5.4 Inlet and pressure valves ................................................... 493.5.5 Safety valve ........................................................................ 493.5.6 Intake filter .......................................................................... 493.6 Compressor lubricants and coolants .................................. 504.1 Pressure definitions.............................................................. 514.2 Operating status.................................................................... 524.2.1 Stopped ( L0) ..................................................................... 524.2.2 Idle ( L1) ............................................................................. 524.2.3 Part-load ............................................................................ 534.2.4 Operating load ( L2) .......................................................... 534.3 Controlling individual compressors .................................... 544.3.1 Intermittent control ............................................................. 544.3.2 Idle mode control ................................................................ 544.3.3 Delayed intermittent control ................................................ 554.3.4 Part-load control ................................................................. 564.3.4.1 Proportional regulation ....................................................... 564.3.4.2 Frequency control ............................................................... 574.4. The ARS control concept ..................................................... 594.4.1 Autotronic ........................................................................... 604.4.2 Ratiotronic .......................................................................... 604.4.3 Supertronic......................................................................... 61IIITable of contentsPart 5Compressed air treatmentChapter Page4.5 Control of several compressors .......................................... 624.5.1 MCS 1 and MCS 2 ............................................................. 624.5.2 MCS 3 ................................................................................ 634.5.3 MCS 4 ................................................................................ 644.5.4 MCS 5 ................................................................................ 654.5.5 MCS 6 ................................................................................ 664.5.6 MCS 7 ................................................................................ 675.1 Why treatment ? .................................................................... 685.1.2 Planning information .......................................................... 695.1.3 Consequences of poor treatment ....................................... 705.1.3 Impurities in the air ............................................................. 715.2 Water in the compressed air ................................................ 725.2.1 Atmospheric humidity ......................................................... 725.2.2 Dew points ......................................................................... 735.2.3 Air moisture content ........................................................... 735.2.4 Quantity of condensate during compression ...................... 745.2.5 Example for calculating quantities of condensate .............. 755.2.6 Quantity of condensate on a humid Summer day .............. 765.2.7 Determining the pressure dew point ................................... 775.2.8 Pressure dew point after removal of pressure .................... 785.3 Compressed air quality......................................................... 795.3.1 Quality classes defined in DIN ISO 8573-1....................... 795.4 Methods of drying ................................................................. 805.4.1 Operating conditions .......................................................... 815.4.2 Condensation by high pressure.......................................... 825.4.3 Condensation by refrigeration drying ................................. 835.4.4 Diffusion by membrane drying............................................ 845.4.5 Sorption by Absorption....................................................... 855.4.6 Sorption by Adsorption....................................................... 865.4.6.1 Heatless regeneration ........................................................ 875.4.6.2 Internal heat regeneration .................................................. 885.4.6.3 External heat regeneration ................................................. 895.4.6.4 Vacuum regeneration ......................................................... 905.4.7 Arrangement of the refrigeration compressed air dryer ...... 915.4.7.1 Dryer before the compressed air receiver .......................... 915.4.7.2 Dryer behind the compressed air receiver .......................... 925.5 Compressed air filters .......................................................... 935.5.1 Basic terminology of filters ................................................. 935.5.1.1 Filter separation rate [ %] ............................................... 935.5.1.2 Pressure drop p ............................................................... 945.5.1.3 Operating pressure ............................................................ 945.5.2 Dust separators .................................................................. 955.5.3 Pre-filters ............................................................................ 965.5.4 Microfilters .......................................................................... 965.5.5 Active carbon filters ............................................................ 995.5.6 Active carbon adsorbers................................................... 1005.5.7 Sterile filters ..................................................................... 101IVTable of contentsPart 7Compressed airrequirementPart 6Disposal of condensatePart 8Determining the size ofthe compressor stationChapter Page6.1 Condensate.......................................................................... 1026.2 Condensate drains .............................................................. 1036.2.1 Condensate drains with manual valves ............................ 1046.2.2 Condensate drains with float control ................................ 1046.2.3 Condensate drains with timer operated solenoid valves... 1056.2.4 Condensate drains with electronic level control ................ 1066.2.5 Condensate drains with float operated level control ......... 1076.3 Condensate treatment ........................................................ 1086.3.1 Oil-water separators ......................................................... 1097.1 Consumption of compressed air by pneumatic devices . 1107.1.1 Consumption of nozzles ................................................... 1107.1.1.1 Compressed air consumption of cylindrical nozzles ......... 1117.1.1.2 Compressed air consumption of paint spray guns ........... 1127.1.1.3 Compressed air consumption of jet nozzles ..................... 1137.1.2 Compressed air consumption of cylinders ....................... 1147.1.3 Compressed air consumption of tools .............................. 1157.2 Determining compressed air requirement ........................ 1177.2.1 Average operation time .................................................... 1177.2.2 Simultanity factor .............................................................. 1187.2.3 Defining compressed air requirement .............................. 1197.2.3.1 Automatic consumer devices............................................ 1197.2.3.2 General consumer devices............................................... 1207.2.3.3 Total compressed air consumption ................................... 1207.2.4 Allowances for losses and reserves ................................. 1217.2.5 FAD Required LB.............................................................. 1217.3 Compressed air loss ........................................................... 1227.3.1 Costs of compressed air loss ........................................... 1227.3.2 Quantifying leakage ......................................................... 1237.3.2.1 Quantifying leakage by emptying the receiver .................. 1237.3.2.2 Quantifying leakage by measuring working time .............. 1247.3.3 Limits for leakage ............................................................. 1257.3.4 Measures for minimising compressed air loss.................. 1257.3.5 Reconstructing a pneumatic network ............................... 1268.1 The type of compressor ...................................................... 1278.1.1 Screw compressors.......................................................... 1278.1.2 Piston compressors.......................................................... 1278.2 Maximum pressure Pmax..................................................... 1288.2.1 Factors influencing cutout pressure Pmax......................... 1288.3 Determining the volume of a compressed air receiver ... 1298.3.1 Recommendations for the volume of compressed airreceivers........................................................................... 1298.3.2 Norm series and operating pressures for sizes ofcompressed air receivers ................................................. 1298.3.3 Volumes of compressed air receivers for compressors .... 130VTable of contentsPart 9The pneumatic systemChapter Page8.4 Compressor cycle intervals................................................ 1318.4.1 Compressor idle times ..................................................... 1318.4.2 Compressor running times ............................................... 1318.4.3 Determining the motor cycle speed.................................. 1328.5 Examples for compressor configuration........................... 1338.5.1 Samples calculation for piston compressors .................... 1338.5.1.1 Determining the maximum pressure Pmax........................ 1338.5.1.2 Determining compressor size........................................... 1348.5.1.3 Volume of the compressed air receiver ............................ 1348.5.1.4 Compressor cycle interval ................................................ 1358.5.1.5 Motor cycling rate of compressor ..................................... 1368.5.2 Samples calculation for screw compressors .................... 1378.5.2.1 Example for determining the maximum pressure Pmax.... 1378.5.2.2 Determining compressor size........................................... 1378.5.2.3 Dimensioning the compressed air receiver ...................... 1388.5.2.4 Compressor cycle interval ................................................ 1388.5.3 Summary on compressor selection .................................. 1398.6 Information on compressor configuration ........................ 1408.6.1 Performance and working pressure.................................. 1408.6.2 Varying working pressure of consumer devices ............... 1418.6.3 Combined compressor systems ....................................... 1419.1 The compressed air receiver .............................................. 1429.1.1 Storing compressed air .................................................... 1429.1.2 Pulsation damping............................................................ 1429.1.3 Condensate collection ...................................................... 1439.1.4 Operation of compressed air receivers............................. 1439.1.5 Installation of compressed air receivers ........................... 1439.1.6 Safety rules for compressed air receivers ........................ 1449.1.6.1 Registration and inspection obligations ............................ 1449.1.6.2 Approved inspection authorities and authorizedpersonnel ......................................................................... 1449.1.6.3 Inspection prior to commissioning .................................... 1459.1.6.4 Registration ...................................................................... 1459.1.6.5 Repetitive inspections ...................................................... 1459.1.7 Fittings on the compressed air receivers .......................... 1479.1.7.1 Safety valve ...................................................................... 1489.2 The compressed air circuit ................................................. 1499.2.1 The structure of a compressed air circuit ......................... 1499.2.1.1 The main line.................................................................... 1499.2.1.2 The distribution line- ring line ........................................... 1509.2.1.3 The distribution line- stub line........................................... 1519.2.1.4 The connection line .......................................................... 1519.2.1.5 Connecting to a collective line with multiple systems ....... 152VITable of contentsPart 10The Installation RoomChapter Page9.3 Tips for planning pipe systems.......................................... 1539.3.1 General planning tips ....................................................... 1539.3.2 Pipeline without compressed air dryer ............................. 1549.3.3 Pipeline system with compressed air dryer ...................... 1559.4 Pressure loss p ................................................................. 1569.4.1 Type of flow ...................................................................... 1569.4.2 The Reynolds number Re ................................................ 1569.4.3 Pressure loss in the pipe system...................................... 1579.5 Dimensioning pipelines ...................................................... 1589.5.1 Maximum pressure drop p ............................................. 1589.5.2 Nominal width of pipelinesComparison [ DN Inch ] ................................................. 1599.5.3 Equivalent pipe length ...................................................... 1609.5.4 Determining the inside diameter diof the pipe by calculation .................................................. 1619.5.5 Determining the inside diameterof the pipe di by graphics .................................................. 1629.5.6 Determining the inside diameterof the pipe di with the aid of a bar graph........................... 1639.6 Choosing the material for pipelines .................................. 1649.6.1 Threaded pipes ................................................................ 1649.6.2 Seamless steel pipes ....................................................... 1659.6.3 Stainless steel pipes ........................................................ 1659.6.4 Copper pipes .................................................................... 1669.6.5 Plastic pipes ..................................................................... 1679.7 Marking pipelines ................................................................ 16810.1 Cooling the compressor ..................................................... 16910.2 Compressor installation ..................................................... 17010.2.1 General information regarding the installation room......... 17010.2.2 Admissible ambient temperature ...................................... 17010.2.3 Fire safety rules for installation rooms .............................. 17110.2.4 Disposal of condensate .................................................... 17110.2.5 Compressor installation instructions................................. 17210.2.6 The space requirement of a compressor .......................... 17210.2.7 Conditions for installing compressed air receivers ........... 17310.3 Ventilation of a compressor station .................................. 17410.3.1 Factors influencing the flow ofcooling air of a Vc of a compressor ................................... 17410.3.2 Definition of the factors influencing the flow ofcooling air Vc to and from a compressor ........................... 17510.3.3 General information for ventilation of compressor rooms . 17610.3.4 Natural ventilation............................................................. 17710.3.4.1 Outlet air aperture required for natural ventilation ............ 17710.3.5 Artificial ventilation ........................................................... 17810.3.5.1 Required ventilator output with artificial ventilation........... 17810.3.5.2 Required inlet air aperture with artificial ventilation .......... 179VIITable of contentsPart 11Heat recoveryPart 12SoundChapter Page10.3.5.3 Example of artificial ventilation of a compressor station ... 18010.3.6 Circulation of cooling-air with inlet and outlet ducts.......... 18110.3.6.1 Air inlet ducts.................................................................... 18110.3.6.2 Extraction of air through a cool-air duct ............................ 18210.3.6.3 Required flow of cooling-air Vd and cross-sectionof duct Ad when using a cool-air duc ................................ 18210.3.6.4 Information concerning ventilation by ducting .................. 18310.3.6.5 Dimensioning the air inlet aperturewhen using an outlet duct ................................................ 18410.3.6.6 Variations of duct-type ventilation..................................... 18510.4 Example installation plans ................................................. 18610.4.1 Installation of a screw-type compressor: an example ....... 18610.4.2 Installation of piston-type compressor: an example.......... 18711.1 The heat balance of a compressor station........................ 18811.2 Room heating ...................................................................... 18911.2.1 Room heating through ducting ......................................... 18911.2.2 Operation of room heating................................................ 19011.2.3 Economy of room heating ................................................ 19011.3 The Duotherm heat exchanger ........................................... 19111.3.1 Duotherm BPT ................................................................. 19111.3.2 Duotherm BSW................................................................ 19211.3.3 How much energy is it possible to save?.......................... 19311.4 Closing remarks concerning heat recovery ...................... 19412.1 The nature of sound............................................................ 19512.1.1 Sound perception ............................................................. 19512.2 Important terminology in acoustics .................................. 19612.2.1 Sound pressure ................................................................ 19612.2.2 Sound level ....................................................................... 19612.2.3 Sound intensity................................................................. 19612.3 Human perception of sound............................................... 19712.3.1 The sound intensity level .................................................. 19712.3.2 Assessed sound level dB ( A ) .......................................... 19712.3.3 Loudness in comparison .................................................. 19812.4 Behaviour of sound............................................................. 19912.4.1 Distance from the sound source....................................... 19912.4.2 Reflection and Absorption ................................................ 19912.4.3 Damping sound ................................................................ 20012.4.5 Dessemination of sound in pipes and ducts ..................... 20012.4.6 Sound pressure level from many sound sources.............. 20112.4.6.1 Several sound sources with the same level ...................... 20112.4.6.2 Two sound sources with different levels ........................... 20112.5 The effects of noise ............................................................ 20212.6 Noise measurement ............................................................ 20312.7 Silencing on compressors ................................................. 203VIIITable of contentsPart 13Costs of compressed airPart 14AppendixChapter PagePart 15Index13.1 Composition of compressed air costs .............................. 20413.1.1 Cost factor ratios .............................................................. 20413.2 Cost-effectiveness calculation for energy costs .............. 205A.1 Symbols ............................................................................... 206A.1.1 Picture symbols defined by DIN 28004 ............................ 206A.1.2 Symbols for contact units and switching devicesas per ISO 1219 ............................................................... 20815.1 Conversion Table ................................................................. 2121Fundamentals of compressed air1. Fundamentals of compressed air1.1 The historyof compressed air1.1.1 The origin of compressed airFig. 1.1:The first compressor - the lungCompressed air, together with electricity, is the most frequentlyused carrier of energy in industry and the crafts today. Butwhereas we learn to use electricity and electrical appliancesfrom a very early age, the possibilities, advantages and essen-tials of compressed air are far less understood.Peoples comprehension of compressed air grew parallel totheir understanding in other technical fields. Its developmentwas only furthered where it was seen to have advantages overother technologies. But compressed air was always beingused, and so clever people were always thinking about how toput it to better use.The first compressor - the lungMany technical applications originate from the earliest days ofmankind. The first use of compressed air was blowing on tinderto fan a flame. The air used for blowing was compressed in thelungs. Indeed, the lung could be called a kind of naturalcompressor. The capacity and performance of this compres-sor is extremely impressive. The human lung can process100 l/min or 6 m3 of air per hour. In doing so it generates apressure of 0,02 - 0,08 bar. In a healthy condition, the reliabilityof the human compressor is unsurpassed and it costs nothingto service.The further development of the lungHowever, the lung proved to be wholly inadequate whenpeople began to smelt pure metals such as gold, copper, tinand lead more than 5000 years ago. And when they startedto make high grade metals, such as iron from ore, furtherdevelopment of compressed air technology was essential.More powerful aids than the lung were needed to generatetemperatures of over 1000 C. At first they used the high windson uplands and the crests of hills. Later, Egyptian and Sumeriangoldsmiths made use of the blast pipe. This brought air directlyinto the embers, which increased the temperature decisively.Even today, goldsmiths all over the world use a similar device.However, this is only useful for melting small quantities ofmetal.2Fundamentals of compressed airFig. 1.2:Picture of the foot-powered bellows in ancient Egypt1.1.2 The first applications ofcompressed airRecognising the properties ofcompressed airFig. 1.3:The catapult of KtesibiosFig.1.4:The temple doors of HeronThe first mechanical compressor - the bellowsThe first mechanical compressor, the hand-powered bellows,was developed in the middle of the third millennium BC. Themuch more powerful foot-powered bellows was invented around1500 BC. This progress was necessary when the alloying ofcopper and tin to make bronze developed into a stable manu-facturing process. The development can be seen in a wall-painting of an ancient Egyptian grave. It was the birth of com-pressed air as we know it today.Hydraulic organStorage and suppression of pulsationThe first deliberate exploitation of energy in the air is handeddown to us by the Greek Ktesibios ( ca. 285 to 222 BC ). Hebuilt a hydraulic organ and used compressed air for thestorage and reduction of vibration.CatapultStorage of energyKtesibios used another property of compressed air, storedenergy, for his catapult. With the aid of air compressed in acylinder, the Greeks catapult generated enough tension topropel missiles.Temple doorsExpansion and the performance of workHeron, an engineer living in Alexandria in the first century BC,found a way to open the doors of a temple automatically bykeeping the flame at the altar inside the building permanentlyalight. The secret was to use the expansion of hot air to forcewater out of one container and into another. Heron recognised,even if unwittingly, that it was possible to perform work bychanging the condition of air.3Fundamentals of compressed airFig. 1.5 :Compressed air to increase energyFig. 1.6 :Compressed air as a means of transportp1p2Fig. 1.7 :Pneumatic brakes in a train ca. 1870Pascals lawIncreasing energyIt was only in the 17th century that a series of learned peoplebegan to study the physical laws applicable to compressed air.In 1663 Blaise Pascal published an essay on increasingenergy by using liquids ( hydraulics ), that was also valid forthe technology of compressed air. He found that the energyexerted by one man at one end of a closed container of waterwas equivalent to the energy exerted by 100 men at anotherend.Transporting objects through pipesPneumatic conveyanceTaking up where Heron left off, the French physicist DenisPapin described in 1667 a method of transporting objectsthrough pipes. He exploited the slight difference in pressureinside a pipe. In doing so he found out that energy wasgenerated at an object inside the pipe. This was recognition ofthe advantage of the high work speeds obtainable by using air.Papin thus laid the foundation stone for pneumatic convey-ance.Pneumatic brakesPower transmissionAs early as around 1810, trains were being powered bycompressed air. In 1869 Westinghouse introduced his pneu-matic brake. His brake motor followed three years later. In thissystem the brakes were applied by over-pressure i.e., the fullbraking effect is obtained if there is a drop in pressure e.g., bythe bursting of a hose.This was the first use of a fail-safe system. Brake systemsbased on this principle are still used in HGVs today.4Fundamentals of compressed airFig. 1.8 :Pneumatic drills in tunnel constructionFig. 1.9 :Compressed air station in Paris 1888Pneumatic postConveyance by compressed airThe idea of trains powered by compressed air was not forgot-ten. In 1863, Latimer Clark together with an engineer namedRammel built a pneumatic conveyance system in London. Itfeatured small trolleys moving completely inside conveyortubes and was designed to transport postal bags and parcels.This system was much more flexible than the heavy, atmos-pheric railways of 1810, and led eventually to the introductionof pneumatic post.Pneumatic post networks soon sprung up in Berlin, New Yorkand Paris. The Paris network reached its peak length of 437 kmin 1934. Even today, pneumatic post systems are still used inlarge industrial operations.Pneumatic toolsTransporting energyWhen the tunnel through Mont Cenis was being built in 1857,the new technology was used in a pneumatically-poweredhammer drill to cut through the rock. From 1861 they usedpneumatically-powered percussion drills, these being sup-plied with compressed air from compressors at both ends ofthe tunnel. In both cases the compressed air was transportedover long distances.When in 1871 the breakthrough in the tunnel was achieved,there were over 7000 m of pipelines on both sides. Thus, forthe first time, the transportability of energy was demon-strated and made known to a wide public as one of theadvantages of compressed air. And from here on, pneumatictools of even greater performance and versatility were devel-oped.Pneumatic networksCentral generation of compressed air and signal transmissionThe experience gained using networks of pneumatic lines andthe development of more powerful compressors led to apneumatic network being installed in the sewage canals ofParis. It was put into commission in 1888 with a centralcompressor output of 1500 kW. By 1891 its output rating hadalready reached 18000 kW.The all-round success of the pneumatic network was under-lined by the invention of a clock, the minute hand of which wasmoved on every sixty seconds by an impulse from the com-pressor station. People had not only seen the possibility oftransporting energy, but also of moving signals over greatdistances through a pneumatic network.The pneumatic network in Paris is unique to this day, and is stillin use.5Fundamentals of compressed airFig. 1.10 :Four-stage adding device with wall radiationelementsSignal processingCompressed air for the transmission and processing of signalsIn the 1950s in the USA the high flow speed of compressed airwas first used for the transmission and processing of signals.Low-pressure pneumatics, also known as fluidics or pneu-monics ( pneumatic logic ), allow the integration of logicalswitching functions in the form of fluidic elements in a verysmall area at pressures of 1.001 to 1.1 bar.The high operating precision of the fluidic logic elements underextreme conditions allowed them to be used in the space anddefence programmes of the USA and the USSR. Immunity toelectromagnetic radiation from exploding nuclear weaponsgives fluidics a special advantage in several sensitive areas.Even so, over the course of time fluidics has largely beensuperseded by electrical and microelectronic technology in thefields of signal and information processing.6Fundamentals of compressed airEngineering uses measures derived from the basic units. Thefollowing table shows the most frequently used units of meas-ure for compressed air.1.2 Units and formula symbolsBasic unit Formula symbol Symbol NameLength l [ m ] MetreMass m [ kg ] KilogrammeTime t [ s ] SecondStrength of current I [ A ] AmpereTemperature T [ K ] KelvinStrength of light I [ cd ] CandelaQty of substance n [ mol ] MolThe SI-units ( Systme International d'Units ) were agreedat the 14th General Conference for Weights and Measures.They have been generally prescribed since 16.10.1971.The basic units are defined independent units of measureand form the basis of the SI-system.Unit Formula symbol Symbol NameForce F [ N ] NewtonPressure p [ Pa ] Pascal[ bar ] Bar 1bar = 100000PaArea A [ m2] Square metreVolume V [ m3] Cubic metre[ l ] Litre 1m3 = 1000lSpeed v [ m / s ] Metre per SecondMass m [ kg ] Kilogramme[ t ] Tonne 1t = 1000kgDensity [ kg / m3] Kilogramme per cubic metreTemperature T [ C ] Degree CelsiusWork W [ J ] JouleEnergy P [ W ] WattTension U [ V ] VoltFrequency f [ Hz ] Hertz1.2.1 Basic units1.2.2 Compressed air units7Fundamentals of compressed airThe air in our environment, the atmosphere, consists of:78 % Nitrogen21 % Oxygen 1 % other gases( e.g.. carbon-dioxide and argon )Compressed air is compressed atmospheric air.Compressed air is a carrier of heat energy.Compressed air can bridge certain distances ( in pipelines ),be stored ( in compressed air receivers ) and perform work( decompress ).As with all gases, the air consists of molecules. The moleculesare held together by molecular force. If the air is enclosed in atank ( constant volume ), then these molecules bounce off thewalls of the tank and generate pressure p.The higher the temperature, the greater the movement of airmolecules, and the higher the pressure generated.Volume ( V ) = constantTemperature ( T ) = is increasedPressure ( p ) = risesBoyle and Mariotte carried out experiments with enclosedvolumes of gas independently of each other and found thefollowing interrelationship:The volume of gas is inversely proportional to pressure.( Boyle-Mariottes Law )1.3 What is compressed air ?1.3.2 The properties of compressed airFig. 1.11:The composition of airFig. 1.13:Air in a closed container1.3.1 The composition of airpVpppppppppppT1.3.3 How does compressed air behave?Compressed airPressure energyHeatFig. 1.12:Air compressionNitrogen78%Oxygen21%other gases1%8Fundamentals of compressed airp0 , T0p1 , T1p0 , V0p1 , V1V0 , T0V1 , T1HeatHeatThe condition of compressed air is determined by the 3measures of thermal state:T = TemperatureV = Volumep = Pressurep V = constantTThis means:Volume constant ( isochore )Pressure and temperature variableWhen the temperature is increased and the volume remainsconstant, the pressure rises.p0T0 = p1T1Temperature constant ( isotherm)Pressure and volume variableWhen the volume is reduced and the temperature remainsconstant, the pressure rises.p0 V0= p1 V1= constantPressure constant ( isobar )Volume and temperature variableWhen the temperature is increased and the pressureremains constant, the volume increases.V0T0 = V1T11.4 Physical fundamentalsconstant volumeisochore compressionconstant temperatureisotherm compressionconstant pressureisobar compression9Fundamentals of compressed air0C1.4.1 Temperature1.4.2 VolumeVolume (V)Norm volume + 8% = Volume0C 20 C0 barabs8 barabsFig.1.14:Showing temperatureThe temperature indicates the heat of a body and is read in Con thermometers or converted to Kelvin ( K ).T [ K ] = t [ C ] + 273,15Volume V [ l, m3]Compressed air in expanded state, open airThe volume is determined, for example, by the size of a cyl-inder. It is measured in l or m3 and relative to 20 C and1 bar.The numbers in our documentation always refers to com-pressed air in its expanded state.d2 VCyl= h4VCyl= Volume [m3]d = Diameter [m]h = Height [m]Normal volume VNorm [ Nl, Nm3]Compressed air in expanded state under normal conditionsThe normal volume refers to the physical normal state as speci-fied in DIN 1343. It is 8% less than the volume at 20 C.760 Torr = 1,01325 barabs= 101 325 Pa273,15 K = 0 COperating volume Voperat [ Bl, Bm3]Compressed air in compressed stateThe volume in operating state refers to the actual condition.The temperature, air pressure and air humidity must be takeninto account as reference points.When specifying the operating volume the pressure mustalways be given, e.g., 1 m3 at 7 bar means that 1 m3 expanded(relaxed) air at 7 bar = 8 bar abs. is compressed and onlyoccupies 1/8 of the original volume.10Fundamentals of compressed airAtmospheric pressure pamb [ bar ]Atmospheric pressure is caused by the weight of the air thatsurrounds us. It is dependent on the density and height of theatmosphere.At sea level, 1 013 mbar = 1,01325 bar= 760 mm/Hg [ Torr ]= 101 325 PaUnder constant conditions atmospheric pressure decreasesthe higher the measuring location is.Over-pressure pop [ barop]Over-pressure is the pressure above atmospheric pressure.In compressed air technology, pressure is usually specifiedas over-pressure, and in bar without the index op.Absolute pressure pabs [ bar ]The absolute pressure pabsis the sum of the atmospheric pres-sure pamb and the over-pressure pop.pabs= pamb + popAccording to the SI-System pressure is given in Pascal [ Pa ].In practice, however, it is still mostly given in bar . The oldmeasure atm ( 1 atm = 0,981 bar-op ) is no longer used.Force FPressure = p = Area A1 Newton 1 N1 Pascal = 1 Pa = 1 m21 m21 bar = 10195 mmWH [ mm water head ]1.4.3 PressureFig.1.15:Atmospheric pressureFig.1.16:Illlustration of different pressuresOver-pressurebarometricair pressurePartialvacuum100 % Vacuumpabspoppvacpambpamb= Atmospheric pressurepop= Over-pressurepvac= Partial vacuumpabs= Absolute pressure11Fundamentals of compressed airVolume flow V [ l/min, m/min., m/h ]The volume flow describes the volume ( l or m ) per unit oftime ( minute or hour ).A distinction is made between the working volume flow ( in-duction rate ) and the volume flow ( output rate ) of a com-pressor.Working volume flow VWor [ l/min, m/min., m/h ]Induction rateThe working volume flow is a calculable quantity on pistoncompressors. It is the product of the cylinder size ( pistoncapacity ), compressor speed ( number of strokes ) and thenumber of cylinders working. The working volume flow is givenin l/min, m/min or m/h.VWor= A s n cVWor= Working volume flow [ l / min]A = Cylinder area [ dm2]s = Stroke [ dm]n = Number of strokes [ 1/ min](compressor speed)c = Number of working cylindersVolume flow V [ l/min, m/min, m/h ]Output rateThe output rate of a compressor is normally declared as thevolume flow.In contrast to the working volume flow, the volume flow is nota calculated value, but one measured at the pressure joint ofa compressor and calculated back to the induction state. Thevolume flow is dependent on the final pressure relative to theinduction conditions of pressure, temperature and relativehumidity. This is why when calculating the induction state themeasured volume flow to induction pressure must be relaxedand to induction temperature it must be re-cooled and dryedto a relative humidity of 0 %.The volume flow is measured according to VDMA 4362,DIN 1945, ISO 1217 or PN2 CPTC2 and given in l/min, m3/minor m3/h. The effective volume flow, i.e., the output that canactually be used, is an important consideration for the designof a compressor. Volume flows can only usefully be comparedwhen measured under the same conditions. This means thatthe induction temperature, pressure, relative air humidity andmeasured pressure must match.1.4.4 Volume flowTDC = Top dead centreBDC = Bottom dead centreTDCBDCFig. 1.18:Cylinder movementWorking volume flowInduction rateFig. 1.17:Working volume flow and volume flow

Volume flowOutput rate12Fundamentals of compressed airNorm volume flow VNorm [ Nl/min, Nm3/min, Nm3/h ]As with the volume flow, the norm volume flow is also meas-ured.However, it does not refer to the induction state, but to a theo-retical comparative value. With the physical norm state thetheoretical values are:Temperature = 273,15 K ( 0 C )Pressure = 1,01325 bar ( 760 mm HG )Air density = 1,294 kg/m3( dry air )rel. humidity = 0 %Operating volume flow VOperat [ Ol/min, Om3/min, Om3/h ]The operating volume flow gives the effective volume flow ofcompressed air.To be able to compare the operating volume flow with the othervolume flows, the pressure of he compressed air must alwaysbe given in addition to the dimension Ol/min, Om3/min orOm3/h.Norm volume flow + 8% = Volume flow0C 20CFig. 1.19:Norm volume flowFig. 1.20:Operating volume flow1 barabs8 barabs13Fundamentals of compressed airDifferent laws apply to compressed air in motion than to sta-tionary compressed air.The volume flow is calculated from area and speed.V= A1 v1= A2 v2A1v2 = A2v1V= Volume flowA1, A2= Cross sectionv1, v2= SpeedThe result of the formula is that:The speed of flow is inversely proportional tothe cross section.Flow can be laminar or even (Ideal),or turbulent ( with backflow and whirling ).Laminar flow ( even flow )low drop in pressureslight heat transitionTurbulent flow ( whirl flow )high drop in pressuregreat heat transition1.5 Compressed air in motion1.5.1 Flow behaviour1.5.2 Types of flowFig. 1.21:Flow behaviourA2A1v1v2Fig. 1.22:Laminar flowFig. 1.23:Turbulent flow14Applications for pneumatics2. Applications for pneumatics2.1 The advantagesof compressed airPneumatics faces increasing competition from mechanical,hydraulic and electrical appliances on all fronts. But pneumaticdevices have fundamental advantages over the other tech-nologies:Easily transportedAir is available everywhere, and there is plenty of it. Sinceoutlet air escapes into the open, there is no need for returnlines. Electrical and hydraulic systems need a return line tothe source.Compressed air can be transported over great distances inpipelines. This allows the installation of central generation sta-tions that can supply points of consumption via ring mainswith a constant working pressure. The energy stored in com-pressed air can be widely distributed in this way.Easily storedIt is easy to store compressed air in purpose-built tanks. Ifthere is a storage tank integrated in a pneumatic network, thecompressor only needs to work when the pressure dropsbelow a critical level. And because there is always a cushionof pressure, a work cycle can be completed even if the powernetwork fails.Transportable compressed air bottles can also be used atlocations where there is no pipe system (e.g., under water).Clean and dryCompressed air does not cause soiling or leave drops of oil ifthe lines are defective. Cleanliness in fitting and operation areextremely important factors in many sectors of industry, e.g.,food, leather, textiles, and packing.LightweightPneumatic devices are usually much lighter than comparableequipment and machinery with electrical power units. Thismakes a big difference with manual and percussion tools( pneumatic screwdrivers and hammers).15Applications for pneumaticsSafe to useCompressed air works perfectly even when there are greattemperature fluctuations and the temperatures are extreme.It can also be used where there are very high temperatures,e.g., for operating forge presses and blast furnace doors.Pneumatic devices and lines that are untight are no risk to thesafety and serviceability of the system.Pneumatic systems and components in general wear verylittle. They therefore have a long working life and a low failurerate.Accident-proofPneumatic elements are very safe with regard to fire, explo-sion and electrical hazards. Even in areas where there is arisk of fire, explosion and extreme weather conditions, pneu-matic elements can be used without large and expensive safetyapparatus. In damp-rooms or outdoors too, there is no dangerwith pneumatic equipment.Rational and economicalPneumatics is 40 - 50 times more economical than musclepower. This is a major point, particularly in mechanisation andautomation.Pneumatic components are cheaper than the equivalent hy-draulic components.There is no need for regular medium changes, as with hy-draulic equipment, for instance. This reduces costs and theservicing requirement, and increases operating times.SimpleThe design and operation of pneumatic equipment is verysimple. For this reason it is very robust and not susceptibleto malfunctioning. Pneumatic components are easy to installand can be re-used later without difficulty. Installation timesare short because of the simple design. The fitters require noexpensive special training.Straight-line movements can be executed without extra me-chanical parts such as levers, cams, eccentric disks, screwspindles and the like.16Applications for pneumaticsOverload-proofCompressed air equipment and pneumatic working parts canbe loaded until they stop without being damaged. This is whythey are considered to be overload-proof.In contrast to electrical systems, the output of a pneumaticnetwork can be overloaded without risk of danger. If the pres-sure drops too much, the work can not be done, but there willbe no damage to the network or its working elements.Fast work mediumThe very high flow speeds allow rapid completion of workcycles. This provides short cut-in times and fast conversion ofenergy into work.Compressed air can achieve flow speeds of over 20 m/s.Hydraulic applications only manage 5 m/s.The pneumatic cylinders reach linear piston speeds of 15 m/s.Maximum control speeds in signal processing lie between 30and 70 m/sat operating pressures of between 6 and 8 bar.With pressures of less than 1 bar it is even possible to obtainsignal speeds of 200 to 300 m/s.Fully adjustableTravel speeds and exerted force are fully and easily adjust-able. Both with linear and rotary movement, force, torque andspeeds can be fully adjusted without difficulty by using throt-tles.17Applications for pneumatics2.2 Pressure rangesCompaction pressure in barLow pressure rangeMedium pressure rangeHigh pressure rangeHigh pressure rangeFig 2.1 :Pressure rangesLow pressure range to 10 barMost pneumatic applications in industry and the crafts lie inthe low pressure range of 10 bar and below.Compressors used : one and two-stage piston compressors single-stage screw compressors with oil-injection cooling two-stage compressors rotary compressorsMedium pressure range to 15 barHGV and other heavy vehicle tyres are filled with compressedair from 15 bar compressors. There are also other specialmachines that operate with such pressures.Compressors used : two-stage piston compressors single-stage screw compressors ( up to 14 bar )with oil-injection coolingHigh pressure range to 40 barThe compressors in this pressure range are generally usedfor starting large diesel engines, testing pipelines and flushingplastic tanks.Compressors used : two and three-stage piston compressors multi-stage screw compressorsHigh pressure range to 400 barOne example of the use of compressed air in the high pres-sure range is the storage of breathing air in diving bottles.High pressure compressors are used in power stations, roll-ing mills and steel works and for leak testing. Compressors ofthis type are also used for compressing utility gases, such asoxygen.Compressors used: three and four-stage piston compressors18Applications for pneumatics2.3 Possible applications forcompressed air2.3.1 Tensioning and clamping withcompressed airFig. 2.2:Pneumatic-mechanical clamp2.3.2 Conveyance by compressed airFig. 2.3:Bridging the heights with a pneumatically poweredelevatorCompressed air is used intensively in all sectors of industry,the crafts, and everyday life. The range of possible applica-tions is diverse and all-embracing. Some of the technical usesare mentioned and explained briefly below.In view of the versatility of this medium it is only possible tooutline a few of the possible applications. The arrangement ofthe chapter can not be unambiguous since the criteria forassessment and differentiation are too varied.Tensioning and clamping with compressed air is mainly usedin applications involving mechanisation and automation. Pneu-matic cylinders or motors fix and position the tools needed forwork processes. This can be done by linear and rotary move-ment, and also by swivel movement. The energy in the com-pressed air is converted directly into force and movementthrough the exertion of pressure. The amount of tensioningforce required must be dispensed with precision.Conveyance by compressed air is found in mechanisationand automation. In these applications, motors and cylindersare used for timed or untimed conveyance, or according towork processes. Automated storage and receipt also belongsin this category, as does the turn-around of tools and otheritems on longer conveyor belts.Another variation of pneumatic transport is the conveyance ofbulk material and liquids through pipes. With this method,granulates, corn, powder and small parts can be quickly andcomfortably conveyed over relatively long distances. The pneu-matic post concept also belongs in this category.19Applications for pneumatics2.3.4 Spraying with compressed air2.3.5 Blowing and flushing withcompressed air2.3.3 Pneumatic drive systemsFig. 2.4:Valveless pneumatic hammerFig. 2.6:Air gun with spiral hoseFig. 2.5:Arc-type metal spraying systemPneumatic drive systems are found in all areas of industryand the crafts. These can perform rotary and linear move-ments. Linear movement with the aid of cylinders in particularis seen as a highly economical and rational application. Theutility work is performed by dropping the pressure and chang-ing the volume of the compressed air.Pneumatic percussion machinery and tools (e.g., pneumatichammers) are of great importance in this category. The en-ergy in the compressed air is converted into kinetic energy fora moving piston. Vibrators and jolting devices belong to thiscategory.Pneumatic power is also used by a multitude of valves andslides, tools, adjustment devices, feed systems and vehicles.With Spraying applications, the energy of the expanding com-pressed air is used to force materials or liquids through a spraynozzle. This procedure is used to apply or atomise varioussubstances.Surface treatment processes, such as sand and gravel blast-ing, shot peening and painting with spray-guns belong to thiscategory. Concrete and mortar are also applied using thismethod.If high temperatures are also used, compressed air can beutilised for applying liquid metals. Arc-type spraying is an ex-ample worthy of mention here..Another application is the atomisation of liquids through spraynozzles, e.g., for spraying weedkillers and insecticides.When blowing and flushing the compressed air itself is thework medium and tool. The flow speed generated by droppingpressure and/or the expanding volume performs the utility work.Examples of this type of work are blowing out glass or plasticbottles, blowing out and cleaning tools and moulds, fixing lighttools for processing or conveyance and flushing out metal chipsand residue. Compressed air in this form can also be used tolet off heat.20Applications for pneumatics2.3.6 Testing and inspection withcompressed air2.3.7 Using compressed air for processcontrolFig. 2.7:Reflex nozzle with impulse emitterFig. 2.8:Diagram of a BOGE screw compressor, air-cooledversion with fully-adjustable output controlIn pneumatic testing and inspection procedures, thechanges in pressure at the measuring point are used to deter-mine spacings, weights and changes in shape. This allowspassing articles to be counted, correct positioning to bechecked and the presence of workpieces to be ascertained.This process is an integral part of many sorting, positioningand processing systems.All pneumatic applications must be controlled by some means.They must receive instructions.In general this is done by press-switches, direction valves andso forth. These control mechanisms are in turn actuated inmany different ways, e.g., by mechanical switches, cams, orby hand. Electrical and magnetic switches are also in wide-spread use. The results determined by pneumatic processcontrol systems can be used directly by direction valves orpress-switches.Pneumatics is of great importance for checking flow processeswith liquids and gases. It is used for the remote control ofvalves, slides, and flaps in large industrial installations.Pneumatics (fluidics) is also used for information processingand logical switching. These logic plans are comparable withintegrated electronic circuits. They require much more space,but are characterised by high operating precision in certainapplications. If the demands on the logic elements are not toohigh, fluidics can offer an alternative.21Applications for pneumatics2.4 Examples of specialisedapplicationsThe following list will give the reader an idea of the many ap-plications of compressed air in industry, the crafts and every-day life. Obviously, it is not possible to list all the possibilitiesfor pneumatics since new areas appear and old ones becomedisused in the course of development and progress. This cantherefore only be an incomplete summary of typical applica-tions to be found in the various sectors of the economy.A list of the typical applications in general mechanical engi-neering has not been included, since pneumatics touches prac-tically every area, and mentioning all would be beyond thescope of this manual.Construction trade Drill and demolition hammers ( hand rams ) Concrete compactors Conveyor systems for brickworks and artificial stonefactories Conveyor systems for concrete and mortarMining Rock drilling hammers and carriage systems Loading machinery, shuttle and demolition cars Pneumatic hammers and chisels Ventilation systemsChemicals industry Raw material for oxidation processes Process control Remote-controlled valves and slides in process circuitsEnergy industry Inserting and withdrawing reactor rods Remote-controlled valves and slides in steam andcoolant circuits Ventilation systems for boiler houses22Applications for pneumaticsHealth system Power packs for dentists drills Air for respiration systems Extraction of anaesthetic gasesThe crafts Staplers and nail guns Paint spray-guns Drills and screwdrivers Angle grindersWood processing industry Roller adjustment for frame saws Drill feed systems Frame, glue and veneer presses Contact and transport control of wooden boards Removal of chips and sawdust from work areas Automatic pallet nailingSteel mills and foundries Carbon reduction in steel production Jolt squeeze turnover machines Bundling machinery for semi-finished products Coolants for hot tools and systemsPlastics industry Transport of granulate in pipes Cutting and welding equipment Blowing workpieces from production moulds Locking mechanisms for casting moulds Shaping and adhesive stationsAgriculture and forestry Plant protection and weed control Transport of feed and grain to and from silos Dispensing equipment Ventilation systems in glasshouses23Applications for pneumaticsFood and semi-luxury food industry Filling equipment for drinks Closing and checking devices Bulk packing and palleting machinery Labelling machines Weighing equipmentPaper-processing industry Roller adjustment and feed machinery Cutting, embossing and pressing machinery Monitoring of paper reelsTextiles industry Thread detectors Clamping and positioning equipment in sewing machines Sewing needle and system cooling Stacking devices Blowing out residual material and dust from sewingEnvironmental technology Forming oil barriers in the water Enriching water with oxygen Keeping lock gates free of ice Slide actuation in sewage plants Increasing pressure in the drinking water supply Mammoth pump for submarine applicationsTraffic and communications Air brakes in HGVs and rail vehicles Setting signals, points and barriers Road-marking equipment Starting aids for large diesel engines Blowing out ballast tanks in submarines24Compressed air generatorsCompressors (compactors)are engines used for pumping and compressing gases to anypressure.Ventilatorsare flow machines that pump nearly atmospheric air.With ventilators only slight changes to density and tempera-ture occur.Vacuum pumpsare machines that induct gases and steam in order to create avacuum.3. Compressed airgeneratorsDynamic compressors are for instance turbo-compressors, bywhich running wheels equipped with blades accelerate thegas to be compressed. Fixed direction gear on the bladesconverts speed energy into pressure energy.Dynamic compressors are to be preferred forlarge quantities of medium and low mediumpressures.On displacement compressors the compression chambercloses completely after taking in the air. The volume is re-duced and the air compressed by force.Displacement compressors are to be preferredfor small quantities of medium and high me-dium pressures.3.1 Compressors ( compactors )3.1.1 Dynamic compressors( Turbo-compressors )3.1.2 Displacement compressors25Compressed air generatorsdisplacement compressors Turbo-compressorsAxial compressor Radial compressoroscillatory rotarywith crank drivewithoutcrank drivesingle-shaftmultiple-shaftRotary vanecompressorLiquid ringcompressorScrewcompressorRoots-compressorpistoncompressorPlungercompressorDiaphragmcompressorCrossheadcompressorFree-pistoncompressorCompressors ( compactors )3.2 Types of compressor The summary shows the compressors divided according totheir operating principle.With all compressors, a distinction is drawn between non-oil-lubricated and oil-lubricated compressors.Spiral typecompressor26Compressed air generators3.2.1 Standard compressors The table shows the typical areas of work for various standardtypes of compressor.Type Symbol Op. diagram Pressure range Volume flow[ bar ] [ m3 / h ]Plunger 10 ( 1-stage ) 120compressor 35 ( 2-stage ) 600Crosshead 10 ( 1-stage ) 120compressor 35 ( 2-stage ) 600Diaphragm low lowcompressorFree piston limited use ascompressor gas generatorRotary vane 16 4500compressorLiquid ring 10compressorScrew 22 3000compressorRoots 1,6 1200compressorAxial- 10 200000compressorRadial- 10 200000compressor27Compressed air generators3.2.2 Piston (reciprocating) compressor Piston compressors draw in air by way of pistons moving upand down, compress it and then push it out. The processescontrol induction and pressure valves.By arranging several compression stages in series it is possi-ble to generate various pressures, and differing quantitiesof air can be generated by using several cylinders.Plunger compressorOn plunger compressors, the piston is connected directly tothe crankshaft via the con-rod.Crosshead compressorThe piston is powered by a piston rod and that by the cross-head.Properties of piston compressors: Highly efficient. High pressures.Fig. 3.1:Symbol for piston compressorFig. 3.2:Op. diagram of plunger compressorFig. 3.3:Op. diagram of crosshead compressorCrosshead28Compressed air generatorsThe piston compressors are differentiated according to thearrangement of their cylinders: Vertical cylinders.No stress on the piston or piston ring through the weightof the piston.Small base area. Horizontal cylinders.Only as multi-cylinder compressor in Boxer construction.Low forces of gravity. This benefit is only noticeable whenoutput is greater. V-, W- or L-type compressors.Good mechanical balance.Low space requirement.Fig. 3.6:Crosshead compressorsHorizontal, L-type, V-type, W-typeFig. 3.4:V-type plunger compressorFig. 3.5:W-type plunger compressor29Compressed air generators3.2.3 Diaphragm compressors The diaphragm compressor belongs to the family of displace-ment compressors.An elastic diaphragm causes the compression. Instead of apiston moving linear between two end positions, the diaphragmis moved in non-linear vibrations. The diaphragm is attachedto the side and is moved by a con-rod. The stroke of the con-rod depends on the elasticity of the diaphragm.Features: Large cylinder diameter. Small stroke. Economical with low output quantities, low pressures,and when generating a vacuum.Fig. 3.7:Symbol for diaphragm compressorFig. 3.8:Op. diagram of diaphragm compressor30Compressed air generators3.2.4 Free piston compressor The free piston compressor belongs to the family of displace-ment compressors.It is a compressor with an integrated two-stroke diesel engine.Compressed air acts on the raised pistons and pushes themback inside, thereby starting the compressor. The combustionair thus compressed in the engine cylinder drives the pistonsapart again upon combustion of the injected fuel. The enclosedair is compressed. After letting out the necessary scavengingair the greater part of the compacted air is pushed out througha pressure holding valve. Any remaining air is pushed back inby the piston for the new cycle. The induction valves draw innew air again.Features: Highly efficient. Smooth-running. Simple principle, but seldom used.In practice, the piston movements need to be synchro-nised and extensive control equipment fitted.a = Pneum. outlet apertureb = Inlet aperturec = Fuel injection nozzled = Exhaust apertureFig. 3.9:Op. diagram of free piston compressorab bcd31Compressed air generators3.2.5 Rotary vane compressor The rotary vane compressor ( lamellar or rotary multi-vane com-pressor) is one of the rotary displacement compressors.The housing and rotary pistons moving inside form the cham-ber for inducting and compressing the medium.A cylindrical rotor on eccentric bearings turns inside a closedhousing. The rotor ( drum) has radial slots along its entire length.Inside the slots, slides move in a radial direction.When the rotor reaches a certain speed, the working slide ispressed outwards against the inner walls of the housing bycentrifugal force. The compression chamber between the ro-tor and the housing is divided by slides into individual cells( work chambers).As a result of the eccentric arrangement of the rotor, the vol-ume increases or decreases during a rotation.The pressure chambers are lubricated by loss lubrication oroil injection.By injecting larger quantities of oil into the compression cham-ber one achieves, in addition to lubrication, a cooling effectand a sealing of the slides against the inner wall of the hous-ing. The injected oil can be separated from the compound ofoil and air after compression and directed back to the oil cir-cuit.Features: Very quiet running. Pulse-free and even output of air. Low space requirement and easy to service. Low efficiency. High maintenance costs due to wear on the slides.Fig. 3.10:Symbol for rotary vane compressorFig. 3.11:Op. diagram of rotary vane compressor32Compressed air generators3.2.6 Liquid ring compressor The liquid ring compressor belongs to the category of rotarydisplacement compressors.The eccentrically borne shaft in the housing with fixed radialpaddle displaces the sealing liquid during rotation. This formsthe liquid ring that seals the spaces between the paddlesagainst the housing.The content of the chamber is changed by the rotation of theshaft, causing air to be inducted, compressed and transported.The liquid generally used is water.Features: Oil-free air ( through oil-free transport medium). Low sensitivity to soiling and chemicals. Liquid disperser required because auxiliary liquid isforced continually into the pressure chamber. Low degree of efficiency.a = Paddle wheelb = Housingc = Inlet apertured = Outlet aperturee = LiquidFig. 3.13:Op. diagram of liquid ring compressorFig. 3.12:Symbol for liquid ring compressor33Compressed air generators3.2.7 Screw compressorFig. 3.14:Symbol of screw compressorFig. 3.15:Op. diagram of screw compressorThe screw compressor is a rotary displacement compressor.Two parallel rotors with differing profiles work in opposite di-rections inside a housing.The intake air is compressed in chambers, which continuouslydecrease in size due to the rotation of the rotors until the finalpressure is reached, and is then forced out of the dischargeoutlet. The chambers are formed by the casing walls and themeshing helical gears of the rotors.Oil-free screw compressorsOn screw compressors that seal without oil, and with whichthe air in the compression chamber does not come into con-tact with oil, the two rotors are connected by a synchronisedtransmission so that the surface profiles do not touch.Screw compressors with oil-injection coolingOn screw compressors with oil-injection cooling only the mainrotor is under power. The secondary rotor turns without con-tact.Features: Small size. Continuous air production. Low final compression temperature.( with oil-injection cooling)Fig. 3.16:Section through screw compressor stage34Compressed air generators3.2.8 Roots compressor The Roots compressor belongs to the displacement family ofcompressors.Two symmetrically shaped rotary pistons turn in opposite di-rections inside a cylindrical chamber. They are connected bya synchronised transmission and operate without contact.The air to be compressed is directed from the intake side intothe compressor case. It is enclosed in the chamber betweenthe wing and case. At the moment in which the piston releasesthe edge to the pressure side the gas flows into the dischargeoutlet and fills the pressure chamber. When the wing turnsfurther, the content of the transport chamber is pressed outagainst the full counter pressure. Constant compression takesplace. The compressor must always work against the full dy-namic pressure.Features: No wear on the rotary piston, and therefore no lubricationis required. Air contains no oil. Sensitive to dust and sand.Fig. 3.17:Symbol of Roots compressorFig. 3.18:Op. diagram of Roots compressor35Compressed air generators3.2.9 Axial compressor Axial compressors are flow devices by which the air flows inalternatingly in an axial direction through a series of rotatingand stationary paddles.The air is first accelerated and then compressed. The paddleducts form randomly expanded channels in which the kineticenergy generated by circulation of the air delays and is con-verted into pressure energy.Features: Uniform output. No oil content in air. Sensitive to changes in load and stress. Minimum output quantities required.Fig. 3.19:Symbol of turbo-compressorFig. 3.20:Op. diagram of axial compressor36Compressed air generators3.2.10 Radial compressor Radial compressors are flow devices in which the air is di-rected to the centre of the rotating running wheel.The air is moved by centrifugal force against the periphery.The rise in pressure is caused by the accelerated air beingdirected through a diffusor before it reaches the next runningwheel. The kinetic energy (speed energy) converts into staticpressure during this process.Features: Uniform output. No oil content in air. Sensitive to changes in load and stress. Minimum output quantities required.Fig. 3.21:Symbol of turbo-compressorFig. 3.22:Op. diagram of radial compressor37Compressed air generatorsPiston compressors operate according to the displacementprinciple. The piston intakes air through the intake valve dur-ing the downwards stroke. It closes at the start of the down-wards stroke. The air is compressed and forced out of thepressure valve. The piston is driven by a crank drive with crank-shaft and conrods.Piston compressors are available with one and several cylin-ders, and in one and multiple-stage versions.Multi-cylinder compressors are used for higher outputs, multi-stage compressors for higher pressures.Single stage compressionCompression to the final pressure in one piston stroke.Two stage compressionThe air compressed in the cylinder in the first stage ( low pres-sure stage ) is cooled in the intermediate cooler and then com-pressed to the final pressure in the second stage ( high pres-sure cylinder ).Single action compressorsOne compression action with one rotation of the crankshaft.Double action compressorsTwo compression actions with one rotation of the crankshaft.Piston speedsWith compression the compression speed or even the motorspeed is of secondary importance. The most important factorin assessing wear is the piston speed. So a compressor witha low speed and large stroke can have a high piston speed.In contrast, compressors with high speeds and a small strokecan have low piston speeds. The piston speed, measured inm/s, is extremely low with BOGE piston compressors. Thismeans minimal wear.3.3 Piston compressors3.3.1 GeneralFig. 3.23:BOGE piston compressorFig. 3.24:PrinciplesIntake Compression38Compressed air generatorsSuction rate - OutputStroke volume flow - Volume flowThe suction rate (stroke volume flow) is a calculated size forpiston compressors. It is the product of cylinder capacity, com-pressor speed (number of strokes ) and the number of intakecylinders. The stroke volume flow is given in l/min, m3/min andm3/h.The output ( free air delivered FAD ) is measured according toVDMA Unit Sheet 4362, DIN 1945, ISO 1217 or PN2 CPTC2.The ratio of output to induction rate is the volumetric efficiencyrate.Clearance areaThe clearance area is a specific dimension located betweenthe top dead centre of the piston and the bottom edge of thevalve.The clearance area includes: Design tolerances Cavities in the valves and valve seats Individual design considerationsDuring the down stroke of the piston the air in the compres-sion expands to atmospheric pressure. Only at this stage andduring the continued downstroke of the piston is air sucked infrom outside.The difference between the suction rate and the output oc-curs because during suction the pressure of the air alreadydrops in the inlet filter, leakages also occur, the air sucked inheats up and re-expansion occurs in the compression space.3.3.2 Suction capacity - output

Suction rateSuction rateVolume flowOutputFig. 3.25:Suction rate and free air deliveredFig. 3.26:Clearance areaC = Clearance areaS = StrokeR = Re-expansionCRS39Compressed air generators3.3.3 Cooling Heat is generated in all compression processes. The degreeof heating depends on the final pressure of the compressor.The higher the final pressure, the higher the compression tem-perature.According to safety rules, the final compression temperatureon compressors with oil-lubricated pressure chambers andsingle stage compression, a maximum 20 kW motor ratingand maximum 10 bar may be up to 220C.With higher pressures and motor ratings a maximum tempera-ture of 200C is allowed. With multiple stage compression andpressures of over 10 bar the maximum final compression tem-perature is 160C.The greatest part of compression heat must therefore be ex-pelled. High compressed air temperatures can be dangerousas a small amount of lubrication oil is absorbed into the com-pressed air during compression, this could be flammable. Afire in the line or the compressor would be the least danger,but with higher temperatures the danger of compressed airexplosion is potentially greater because the ratio of oxygencontained is far greater than atmospheric air.Each compressor stage therefore has an intercooler andaftercooler installed in order to cool the compressed air.The quantity of heat to be removed by cooling depends on thefree air delivered and the pressure. Higher pressure compres-sors have two, three, or more cylinders. The cylinders arelocated in the best position in the air flow of the cooling venti-lator wherever possible. In order to intensify heat extraction,the surfaces of the cylinders and cylinder heads are producedwith generous ribbing. However, the intensive cooling and rib-bing of the compressor is not enough to obtain a minimumcompressed air temperature. The compressed air must alsobe cooled by an intercooler between the first and second stagesand an the aftercooler behind the second stage. If this coolingis not sufficient, multi-stage compression is necessary.Safety regulation VGB 16 9 for oil-lubricated reciprocatingcompressors stipulates that the cooling air temperature mustfall to between 60C and 80C after the last compression stage.It is also beneficial for the consumer to have a low compressorair outlet temperature, because the cooler compressed air con-tains less moisture. Apart from this, downstream equipment,such as the compressor receiver and air treatment compo-nents can be designed for low compressed air temperaturesand thus be purchased at less cost. The air outlet temperatureon air-cooled piston compressors is approx. 10 - 15C aboveambient temperature, depending on the quality of the com-pressor.Fig. 3.27:Direction of cooling air on a piston compressorFig. 3.28:After-cooler as turbulence lamellar cooler40Compressed air generators Compression of nearly all technical gases possible Economical compression of pressures up to 40 bar Can be used as a booster compressor Easy control Economical start-stop-operation ( no idle running time )3.3.6 Advantages of reciprocatingpiston compressorsPiston compressors are mainly of the air-cooled variety.Cold air has the advantage that it is almost everywhere inunlimited quantities.The cold air is generated by a ventilator. The ventilator forcesthe cold air over the intercooler and aftercooler and over thecompressor.During compression and cooling stage of the compressed air,condensate forms inside the cooler. Because of the flow speedof the compressed air, the condensate is taken out of theaftercooler by the air, and into the pipe network and com-pressed air tank.3.3.4 CoolantPiston compressors are normally controlled by pressureswitches. The pressure switches must be located in a calmarea of the compressed air. This is in the compressed air re-ceiver, for example, and not in the pipeline between the com-pressor and the receiver.The pressure switch stops the compressor at maximum pres-sure and switches it back on at 20 % below maximum pres-sure. The actuation is therefore 8 :10 bar and 12 :15 bar.A smaller differential is not recommended because the com-pressor will then cycle too often and the wear on the compres-sor and the motor increases. The cut-in pressure can be low-ered with the cut-out pressure remaining constant. This hasthe advantage that the compressor has longer running timesbut longer stationary times too. The cut-in pressure may notbe lower than the minimum pressure of the pneumatic net-work.Piston compressors do not continue running (running-on) butswitch off immediately after the maximum pressure is reached(intermittent operation).Piston compressors are particularly suitable as peak load ma-chines. The compressor only switches on when there is anincreased demand for compressed air and switches off with-out run-on time when the maximum pressure is reached, i.e.,saving approx. 30 % energy consumption in idling mode.3.3.5 Control of reciprocating pistoncompressorsFig. 3.29:Pressure switch41Compressed air generators3.3.7 Components of a piston compressorCrank case Inlet filterSafety valvePressureswitchCoolerDrive motorFig. 3.30:Layout of a piston compressorCondensatedrainCompressedair connection42Compressed air generatorsIn contrast to the piston compressor, the screw compressor isa relatively new construction. Although the principle was de-veloped as early as 1878 by Heinrich Krigar in Hannover, theconstruction was only perfected after the second world war.The Swedish company "Svenska Rotor Maskiner" ( SRM) de-veloped the screw compressor technically to series standard.Screw compressors operate on the displacement principle.Two parallel rotors with different profiles work in opposite di-rections inside a housing.3.4 Screw compressors3.4.1 General3.4.2 Compression process The intake air is compressed to final pressure in chamberswhich continuously decrease in size through the rotation ofthe screw rotors. When the final pressure is reached the air isforced out through the discharge outlet. The compressionchambers are formed by the casing walls and the meshinghelical profiles of the rotors.Intake ( 1 )The air enters through the inlet aperture into the open screwprofiles of the rotors on the intake side.Compression ( 2 ) + ( 3 )The air inlet aperture is closed by the continued rotation of therotors, the volume reduces and the pressure increases.Oil is injected during this process.Discharge ( 4 )The compression process is completed. The final pressure isreached and the discharge begins.Fig. 3.31:Section through a screw compressor air endFig. 3.32:The compression process in a screw compressorstageSuction sideSuction sideSuction sideSuction sidePressure sidePressure sidePressure sidePressure side43Compressed air generatorsBOGE screw compressors draw in atmospheric air throughthe cyclonic suction filter 1 fitted with a paper microfilter car-tridge and with soiled filter facility. After passing through themulti-function suction controller 2 the air enters the compres-sor stage and is compressed 4. Continuously cooled BOGEoil is injected 3 into the compressor stage. The oil absorbs andremoves the heat generated during the compression processwhich increases in temperature to approx. 85C. Accordingto EC machinery guidelines the final maximum compressiontemperature may not exceed 110C.A large proportion of the oil is separated from the compressedair in the combined air/oil separation vessel 5. The residual oilis removed by the spin-on fine oil separator 6, which removesthe residual oil in the compressed air down to only approx.1-3 mg/m3.The compressed air then passes through a minimum pres-sure valve 7 into the compressed air aftercooler 9 where it iscooled down to a temperature of only 8 C above ambient andis then directed through the standard BOGE stop valve intothe compressed air system.The oil in the oil separator is cooled from 85C to 55C in theamply dimensioned oil cooler 8. It then passes through a re-placeable spin-on oil filter 10. A thermostatic valve 11 in the oilcircuit ensures that the oil temperature is ideal in every oper-ating phase.3.4.3 Method of operation1 = Intake filter with paper microfilter insert2 = Multifunction suction controller3 = Oil injection4 = Compressor air end5 = Oil separator tank6 = Spin-on oil separator cartridge7 = Minimum pressure valve8 = Oil cooler9 = Aftercooler parallel to flow of cool air10 = Oil microfilter11 = Thermostat valve12 = Cleaning aperture476121095118312Fig. 3.33:Sectional diagram of aBOGE S-series screw compressor44Compressed air generators3.4.4 Oil circuit The oil injected into the compressor stage performs the fol-lowing functions: Extraction of compression heat (cooling) Sealing the gap between the rotors and their housing Lubricating the bearings1 = Compressed air/oil separator vesselThe oil is separated from the compressed air by reducing theair flow velocity in the separator vessel in which the oil collectsSystem pressure forces this oil out of the separator vesselinto the compressor stage.2 = Thermal bypass valveThe thermal bypass valve directs the oil through the oil cooleror through a bypass (e.g., in the warm-up stage).The oil isthus always at its optimum operating temperature.3 = Oil cooler (air or water)The oil cooler reduces the oil temperature to optimum condi-tions prior to injection into the compressor stage.4 = Oil filterThe oil filter retains impurities from the oil and prevents prob-lems of contamination in the oil circulation system.5 = Compressor air endThe oil injected in the compressed air is directed back into thecompressed air/oil vessel, where it is separated by gravita-tional forces.6 = Scavenging lineThe compressor air end draws any residual oil that has col-lected in the separator back into the oil circuit via the scaveng-ing line.Fig. 3.34:Components of the oil circuit45 621345Compressed air generators3.4.5 Pneumatic circuitFig. 3.35:Components of the pneumatic circuit7 8 65 4 32 1The air sucked into the compressor air end is compressed tofinal pressure by the rotors.1 = Intake filterThe intake filter cleans the air drawn in by the compressorstage.2 = Suction controllerThe suction controller opens (operation mode) or closes (idlingmode and stopped) the intake line, depending on the operat-ing status of the compressor.3 = Compressor air endThe compressor stage compresses the intake air.4 = Compressed air/oil vesselInside the compressed air/oil vessel the compressed air andoil are separated by gravity.5 = Oil separatorThe oil separator removes the residual oil from the compressedair.6 = Minimum pressure valve MPVThis valve opens only when the system pressure has risen to3.5 bar, which causes a fast build-up of system pressure andassures lubrication in the start-up and pressure phase of thecompressor. When the compressor is switched off the mini-mum pressure valve prevents compressed air from flowingout of the compressor.7 = Compressed air aftercooler (air cooled)The compressed air is cooled in the aftercooler. During thisphase, a large proportion of the moisture in the air condensesout.8 = Stop valveThe screw compressor can be isolated from the system viathe stop valve located at the outlet of the compressor.46Compressed air generators when compressed air is required on a continuous basis ideal as a base load machine economical with 100 % operating availability proportionale control possible ideal for use with frequency controllerThe oil removes approx 85% of compression heat from screwcompressors with oil injected cooling. When using a heat ex-changer the heat can be extracted from the oil and used forutility or water heating.The water passing through the heat exchanger is heated to+70C. The quantity of water heated depends on the tempera-ture difference.3.4.6 Heat reclamation3.4.8 Advantages of screw compressorsFig. 3.36:Heat exchanger BOGE-DUOTHERM

Fig. 3.37:Intake control with ventilation/control valveThe suction controller controls the intake line of the screwcompressor. Fully unloaded start-up through closed controllers. Seals hermetically on idling, stopped and emergency cut-out.3.4.7 Intake control47Compressed air generators3.4.9 Main components of a screw compressorFig. 3.38:Layout of a screw compressorIntake filter Control panelDrive motorCompressor air endOil filterCompressed air/oilseparator vesselCompressed air/oilcombi-coolerOil separatorSuction controllerCabinet airinlet filter48Compressed air generators3.5 Components3.5.1 Drive motor Drive motors are normally AC motors and mainly operate at aa speed of 3.000 min-1. The appropriate compressor speed isobtained by drive belt transmission.Normal drive motor supply is TEFV (totally enclosed fan vented)IP 55 class F insulation.Fig. 3.39:Drive motor with belt and tensioner3.5.2 Drive belts The compressor is driven via drive belt transmission.Using the BOGE patented GM-drive system on screw com-pressors, drive belts are practically maintenance-free and havea calculated design life of up to 25,000 hours, depending onsite conditions.3.5.3 Belt tensioning Motors on piston compressors are normally located on a slid-ing plate for belt tensioning. The plate is fitted with a threadedcentral spindle which together with parallel guides ensureaccurate alignment of the drive belts across the pulleys.BOGE screw compressors are equipped with the patentedBOGE-GM-drive system. This take account of different belttension forces caused by motor weight, start-up torque andrunning torque, and ensures that compressors have constantbelt tension in every operating stage, without the need forretensioning and alignment on belt change.Fig. 3.40:BOGE-GM-drive system49Compressed air generators3.5.4 Inlet and pressure valves The tongue valve controls the inlet and outlet of air in the cyl-inder chamber of the piston compressor.BOGE-ferax-tongue valves have fewer components than con-ventional valves, with friction-free operation, minimal deadspace flow resistance. This means more FAD, higher valveworking life expectancy and practically no carbonised oil de-posits on the valves, which can be produced by high compres-sion temperatures.Fig. 3.41:BOGE-ferax-Tongue valveThe safety valve must blow off the full output of the compres-sor at 1.1 times the nominal pressure of the compressed airtank.3.5.6 Intake filter Screw compressors draw in atmospheric air through the airinlet filter inside the compressor cabinet and through the suc-tion filter with paper microfilter cartridge. The inlet filter sepa-rates solid impurities such as dust particles from the intakeair, minimising wear in the compressor and providing the cus-tomer with clean compressed air.In dusty conditions ( e.g., cement works ) paper insert filtersare used. These have a higher separation rate than standardwet air or foam filtration.The filter inserts can be cleaned on larger compressors. Thereis a possibility to monitor the intake filter for pressure differen-tial, allowing soiled filters to be recognised at an early stage.Fig. 3.43:Intake filter with paper insertDust separator Paper filter insertAutomatic dust extraction3.5.5 Safety valveFig. 3.42:Safety valve on screw compressor50Compressed air generators3.6 Compressor lubricantsan