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COMPRESSORSTHEMAINDIFFERENCEBETWEENPUMPSANDCOMPRESSORSISTHATTHEFLUIDDELIVEREDBYCOMPRESSORSAIRISCOMPRESSEDANDUNDERPRESSUREATTHETIMEITISDELIVERED,EVENIFTHEREISNOLOADONTHESYSTEMMOSTDEVICESUSEDTOCOMPRESSAIRAREVERYSIMILARINCONCEPTANDPERHAPSEVENINHARDWARETOHYDRAULICPUMPS,ANDSELECTIONCONSIDERATIONSARESIMILARTHEONLYOTHERSUBSTANTIVEDIFFERENCEISTHATMOSTHYDRAULICSYSTEMSAREPOWEREDBYASINGLEPUMPTHATISACTUALLYAPARTOFTHESYSTEM,WHEREASAHOSTOFPNEUMATICSYSTEMSAREOFTENPOWEREDBYASINGLECOMPRESSOR,WHICHISALMOSTAUTILITYINTHEPLANTLIKEWATERORELECTRICSERVICENEVERTHELESS,MANYSMALLCOMPRESSORSAREAVAILABLEFORSPECIFIC,DISCRETEJOBS；TYPICALLYTHEYAREPOSITIVEDISPLACEMENTCOMPRESSORSDYNAMIC,ORNONPOSITIVEDISPLACEMENTCOMPRESSORSARETYPICALLYLARGER,FACILITYTYPEUNITSCOMPRESSORSAREFAIRLYSIMPLEDEVICES,CAPABLEOFLONGPERIODSOFMAINTENANCEFREEOPERATIONIFPROPERLYINTEGRATEDINTOPNEUMATICSYSTEMSYETTIMEANDAGAINTHEYSUFFERFROMEARLYFAILURESBECAUSEOBVIOUSPRECAUTIONSWEREIGNOREDDURINGSYSTEMDESIGNFOURBASICRULESCANPROVIDESUBSTANTIALIMPROVEMENTINCOMPRESSORLIFEWITHONLYMODERATEDESIGNEFFORTPUMPSANDCOMPRESSORSSHOULDBESIZEDTOPROVIDEATLEASTTHEREQUIREDPRESSUREANDFLOW,ANDPREFERABLY10TO25MOREFILTERSSHOULDBESELECTEDTOPROTECTTHEPUMPINGUNIT,ANDSOMETIMESTOPROTECTDOWNSTREAMCOMPONENTSORPRODUCTSASWELLRELIEFVALVESSHOULDBESELECTEDTOKEEPPRESSUREORVACUUMATAPPROPRIATELEVELSPUMPINGUNITSSHOULDBEPLACEDINACLEAN,COOL,DRYENVIRONMENTBELLOWSCOMPRESSORSCONSISTOFAWELDEDMETALBELLOWSCONNECTEDTOINLETANDOUTLETPORTSWITHCHECKVALVESTHESECOMPRESSORSTYPICALLYCOVERTHEPRESSURERANGEUPTO10PSIG,ANDAREUSEDINPOLLUTIONDETECTINGANDMEASURINGDEVICES,GASSAMPLINGINSTRUMENTS,ANDMEDICALAPPLICATIONSLUBRICATIONISNOTNEEDED,ALLOWINGHIGHPURITIESTOBEMAINTAINEDVANECOMPRESSORSARESIMPLEMACHINESWITHFEWMOVINGPARTSLIKETHEIRHYDRAULICCOUNTERPARTS,VANEPUMPS,THECOMPRESSORSAREINEXPENSIVE,WITHLOWOPERATINGCOST,ANDLOWSTARTINGTORQUEREQUIREMENTTHEYARECOMPACTANDRELATIVELYVIBRATIONFREE,WITHLITTLEPULSATIONINTHECOMPRESSOROUTPUTTHESLIDINGVANESARECLOSELYFITTEDINTHEROTORSLOTSANDWEARVERYLITTLEDURINGOPERATIONTHESECOMPRESSORSAREAVAILABLEINPOWERRANGESFROM10TO500HP,ATPRESSURESTO150PSIRECIPROCATINGCOMPRESSORSCONSISTOFAPISTONMOVINGWITHINTHECYLINDERTOTRAPANDCOMPRESSTHEGASINPRINCIPLE,SUCHAUNITISLIKEANAUTOMOBILEENGINE,WITHTHEPISTONSCOMPRESSINGTHEGASANDVALVESCONTROLLINGITSINLETANDOUTFLOWSSIZESRANGEFROMLESSTHAN1TOOVER5,000HPRECIPROCATINGCOMPRESSORSHAVEGOODPARTLOADEFFICIENCIESANDAREUSEFULFORWIDEVARIATIONSINOPERATINGCONDITIONSDIAPHRAGMCOMPRESSORSAREAMODIFICATIONOFTHERECIPROCATINGCOMPRESSORCOMPRESSIONISPERFORMEDBYTHEFLEXINGOFAMETALORFABRICATEDDIAPHRAGMWHICHISCAUSEDBYTHEMOTIONOFARECIPROCATINGPISTONINACYLINDERUNDERTHEDIAPHRAGMTHESPACEBETWEENTHEDIAPHRAGMANDTHEPISTONISUSUALLYFILLEDWITHLIQUIDLOBEDROTORCOMPRESSORSHAVETWOROTATINGELEMENTSTHATREVOLVEINOPPOSITEDIRECTIONSINACHAMBERINMOSTCOMPRESSORS,THEROTORSDONOTACTUALLYTOUCHANDDONOTDRIVEEACHOTHER,BEINGDRIVENINSTEADBYTIMINGGEARSBECAUSETHEROTORSDONOTACTUALLYTOUCH,AIRLEAKSBETWEENTHEMATASMALLBUTCONSTANTRATETHISLEAKAGE,CALLEDSLIP,ISCONSTANTFORAGIVENCOMPRESSORATAGIVENPRESSUREFORHIGHESTEFFICIENCY,THESECOMPRESSORSSHOULDBEOPERATEDATMAXIMUMSPEEDTHEYAREAVAILABLEINPOWERRANGESFROM7TO3,000HP,DELIVERINGPRESSURESTO250PSIBECAUSETHEINTERNALLOBESDONOTCONTACT,THEYNEEDNOLUBRICATIONLIQUIDPISTONCOMPRESSORSHAVENOMOVINGPARTSINWEARINGCONTACTAROTORWITHMULTIPLEFORWARDCURVEDBLADESROTATESINANELLIPTICALCASINGFLUID,TRAPPEDWITHINTHECASING,ISCARRIEDAROUNDTHEINNERPERIPHERYBYTHEBLADESSPACEBETWEENTHEBLADESCHANGESVOLUMEDUETOTHEELLIPTICALFLUIDPATH,ANDTHEINNERSURFACEOFTHELIQUIDRINGTRAPPEDBETWEENTHEBLADESSERVESASTHEFACEOFALIQUIDPISTONTHESECOMPRESSORSACCEPTLIQUIDSLUGSANDFINEPARTICLESWITHOUTSERIOUSDAMAGELUBRICATIONISREQUIREDONLYINBEARINGSLOCATEDOUTSIDETHEPUMPHOUSINGTHESECOMPRESSORSDELIVERUPTO150PSITHROUGHOUTTHERANGEOF10TO500HPCENTRIFUGALCOMPRESSORSAREBESTSUITEDTOMOVINGLARGEVOLUMESOFAIRATRELATIVELYLOWPRESSURESBASICALLY,THEYCONSISTOFAHIGHSPEEDROTATINGIMPELLER,ADIFFUSERSECTIONWHEREVELOCITYISREDUCEDANDPRESSUREINCREASED,ANDACOLLECTORSECTIONTHATFURTHERREDUCESVELOCITYANDINCREASESPRESSURECENTRIFUGALCOMPRESSORSCANHANDLEHIGHFLOWDEMANDSWELL,BUTWHENDEMANDDECREASESMUCHBELOWRATEDFLOWANDOUTPUTPRESSURERISES,THECOMPRESSORSCANSURGEINSURGE,THEPRESSUREFIELDATTHECOMPRESSOROUTLETVARIESRANDOMLYIFALLOWEDTOCONTINUE,THISCONDITIONCANDAMAGEBEARINGS,BLADES,ANDEVENTHEHOUSINGITSELFCENTRIFUGALCOMPRESSORSTYPICALLYUSEFROMTWOTOSIXSTAGES,SUPPLYINGFROM400TO3,000CFMATSPEEDSTO20,000RPMREGENERATIVEBLOWERSALSOKNOWNASPERIPHERALBLOWERSUSEADISCLIKEIMPELLERWITHBLADESMOUNTEDAROUNDITSOUTSIDEEDGEASTHEIMPELLERREVOLVES,AIRISDRAWNINTOTHESPACEBETWEENTHEBLADESCENTRIFUGALFORCEMOVESTHEAIRINASPIRALPATHOUTWARDTOTHEHOUSING,WHEREITSLIPSBYTHEINITIALBLADEANDRETURNSTOTHEBASEOFTHESUCCEEDINGBLADE,WHERETHEPROCESSISREPEATEDINSOMEMODELS,AFLOWSPLITTERCREATESTWOFLOWPATHS,SOTHATTHEAIRMUSTMAKETWOCIRCUITSAROUNDTHEIMPELLERINOTHERMODELS,THESPLITTERISOMITTED,ANDTHEAIRMAKESONLYONECIRCUITBEFOREEXITINGREGENERATIVEBLOWERSPROVIDEAIRFLOWSUPTO1,000CFMANDPRESSURESTO8PSIHELICALCOMPRESSORSLOOKLIKETWOGIANTSCREWSMESHINGTOGETHER；THEYWORKMUCHLIKEHYDRAULICS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