Compressed Air and Gas Handbook Chapter Four

CompressedAir&GasInstitute•1300SumnerAvenue•Cleveland,OH44115Phone:[phone]•Fax:[phone]•E-mail:[e-mail]™204CompressedAirDistribution(Systems)ChApter44CompressedAirDistribution(Systems)CompreSSeDAirDiStributionSyStemSWhenacompressedairdistributionsystemisproperlydesigned,installed,operatedandmaintained,itisamajorsourceofindustrialpower,possessingmanyinherentadvantages.Compressedairissafe,economical,adaptableandeasilytransmittedandprovideslaborsavingpower.Thecostofacompletecompressedairsystemandpneumatictoolsisrelativelysmallincomparisonwiththesavingseffectedbytheiruse.objectoftheCompressedAirDistributionSystemTheprimaryobjectofacompressedairdistributionsystemistotransportthecompressedairfromitspointofproduction(compressors)toitspointsofuse(applications)insufficientquantityandqualityandatadequatepressureforeffi-cientoperationofairtoolsandotherpneumaticdevices.However,manyotherconsiderationscomeintothedesignofthesystemtoensuretheefficiencyandsafetyofthetotalsystem.Thesewillbediscussedinthischapter.Theseinclude:•Airvolumeflowrate•Airpressurerequirements•Type(s)andnumberofcompressors•Airquality•Airsystemefficiency•Airsystemsafety•Airsystemlayout•AirvolumeflowraterequirementsCompressedAir&GasInstitute•1300SumnerAvenue•Cleveland,OH44115Phone:[phone]•Fax:[phone]•E-mail:[e-mail]™205CompressedAirDistribution(Systems)AirVolumeFlowraterequirementsThepropercapacitytoinstallisavitalandbasicquestionandoftenmisunder-stood.Thecapacityratingofaircompressorsgenerallyispublishedintermsof“freeair,”whichisatatmosphericconditionsofpressure,temperatureandrelativehumidityandnotatthepressure,temperatureandrelativehumidityrequiredattheairtoolorpneumaticdevicetobeoperated.TheApplicationschapterofthisbookcontainsmanyillustrationsofcurrentusesofcompressedairpower.Theairtoolschapteralsoprovidesmuchusefulinformationonapplicationsofairpoweredtoolsandotherpneumaticdevices.Astudyofair-operateddevicesinatypicalmanufacturingplantwillshowthatsomeofthesedevicesoperatealmostconstantlywhileothersoperateinfrequentlybutmayrequirearelativelylargevolumeofairwhileinuse.Italsowillbefoundthattheamountofairactuallyusedbytheindividualdeviceswillvaryconsiderablyindifferentapplications.Thetotalairrequirementthereforeshouldnotbethetotaloftheindividualmaximumrequirementbutthesumoftheaverageairconsumptionofeach.Sufficientcontrolledstoragecapacityofcompressedairalsoisessentialtomeetshort-termhighvolumedemands.Recommendationsforefficientcomponentsforthecompressedairsystemhavebeendiscussedinearlierchapters.Thischapterdealswiththecompressedairdistributionsystemwhichfeedstheproductionoperation.Properdesignofthedistributionsystemisessentialtoavoidenergywasteandtoensureproperuseofallpneumaticdevices.Determinationoftheaverageairconsumptionisfacilitatedbytheuseoftheconceptofloadfactor.Pneumaticdevicesgenerallyareoperatedonlyintermit-tentlyandoftenareoperatedatlessthanfullloadcapacity.Theratioofactualairconsumptiontothemaximumcontinuousfullloadairconsumption,eachmeasuredincubicfeetperminuteoffreeair,isknownastheloadfactor.Itisessentialthatthebestpossibledeterminationorestimateofloadfactorbeusedinarrivingattheplantcapacityneeded.Twoitemsareinvolvedintheloadfactor.Thefirstisthetimefactor,whichisthepercentageofworktimeduringwhichadeviceactuallyisinuse.Thesecondistheworkfactor,whichisthepercentageoftheairrequiredformaximumpossibleoutputofworkperminutethatisrequiredfortheworkactuallybeingperformedbythedevice.Forexample,theairconsumptionofagrinderwithfullopenthrottlevariesconsiderably,dependingonhowhardtheoperatorappliesthegrindingwheelagainsttheworkpiece.Theworkfactoralsoisaffectedbythesys-temoperatingpressure.Forexample,asystempressureof125psigwillprovideaworkfactor22%higherthanasystempressureof100psig.(SeeTable4.10).Theworkfactorthereforeistheratio(expressedasapercentage)oftheairconsumptionunderactualconditionsofoperation,totheairconsumptionwhenthetoolisfullyloaded.Theloadfactoristheproductofthetimefactorandtheworkfactor.Inoneplantstudied,theairactuallyconsumedby434portableairtoolsonproductionworkwasonly15%ofthetotalratedfulltimeairconsumptionofallthetools.CompressedAir&GasInstitute•1300SumnerAvenue•Cleveland,OH44115Phone:[phone]•Fax:[phone]•E-mail:[e-mail]™206CompressedAirDistribution(Systems)ChApter4Indesigninganentirelynewcompressedairdistributionsystem,itishighlydesirabletoutilizeexperiencewithasimilarplant.Theestablishedloadfactorcanbeusedasthebasisofagoodestimateforthenewsystem.Alogofpressuresthroughoutanexistingfacilitywillrevealtrends,includingpeaksandlullsindemandandpotentialirregularitiestobeavoidedinthenewsystem.Anothersourceofthistypeofinformationisthemanufactureroftheairtoolsandpneu-maticdevicesinvolved.Table4.1,showsthemaximumairrequirementsofvarioustoolsandcanbeusedforpreliminaryestimates.Thesefiguresareapproximateandindividualtoolsfromdifferentmanufacturersmayvarybymorethan10%fromthefiguresgiven.Sinceloadfactormayvaryconsiderablyfromoneplanttoanother,anygeneralfiguresshouldbeusedwithcaution.Forexample,onemanufactur