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外文翻译--压缩机.doc

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外文翻译--压缩机.doc

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;THEYWORKMUCHLIKEHYDRAULICSCREWPUMPSMAXIMUMPRESSUREFROMTHESEMACHINESISAPPROXIMATELY125PSIINSINGLESTAGECONFIGURATIONSHELICALCOMPRESSORSMAYBEEITHEROILFLOODEDORDRYDRYHELICALCOMPRESSORS,LIKELOBEDUNITS,REQUIRETIMINGGEARSTOMAINTAINPROPERCLEARANCEBETWEENTHEROTATINGELEMENTSTHESEUNITSAREMOSTEFFICIENTLYOPERATEDATHIGHCONTINUOUSSPEEDSFLOODEDCOMPRESSORSDONOTREQUIREANYTIMINGGEARS,BECAUSETHEOILLADENSCREWSURFACESCANDRIVEEACHOTHERHOWEVER,OILSEPARATORSARENEEDEDTOREMOVETHEOILFROMTHEAIRASITLEAVESTHECOMPRESSORTHEYAREAVAILABLEOVERAPOWERRANGEOFABOUT7TO300HPSINGLESCREWCOMPRESSORSAREBASEDONTHESAMEPRINCIPLEASHELICALCOMPRESSORSASTHECENTRALSCREWROTATES,AIRTRAPPEDBETWEENTHESCREWTEETHISCOMPRESSEDAGAINSTTHESTARSHAPEDROTORSTHESECOMPRESSORSTENDTOHAVELOWVIBRATIONANDNOISELEVELS,ANDLOWDISCHARGEPRESSURESLUBRICATIONISREQUIREDPUMPSVACUUMPUMPSINPRINCIPLE,INDUSTRIALVACUUMPUMPSAREMERELYCOMPRESSORSRUNWITHTHEINLETATTACHEDTOTHEVACUUMSYSTEMANDTHEOUTLETOPENTOEXHAUSTINSMALLERSIZES,COMPRESSORSANDVACUUMPUMPSAREOFTENIDENTICALMACHINESHOWEVER,INTHELARGESIZESTHATMIGHTPOWERAPLANTWIDEVACUUMSYSTEM,THEMACHINESDIFFERINMINORWAYSTHATAREINTENDEDTOENHANCEEFFICIENCYFORONEAPPLICATIONORTHEOTHERMANUFACTURERSSTRONGLYADVISETHATTHESAMEMACHINENOTBEUSEDFORBOTHVACUUMANDCOMPRESSIONATTHESAMETIMETHEHEAVYLOADSWILLDAMAGEITTHREECRITERIACONTROLPUMPSELECTIONDEGREEOFVACUUMPRODUCED,RATEOFAIRREMOVAL,ANDPOWERREQUIREMENTHOWEVER,APPLICATIONSSUCHASFILTRATIONMAYSUBJECTTHEUNITTOTHEINGESTIONOFFOREIGNMATERIALTHEFIRSTPUMPPERFORMANCECRITERIONISTHEVACUUMITPRODUCESMANUFACTURERSPROVIDEAMAXIMUMVACUUMRATINGEXPRESSEDASABSOLUTEPRESSUREINMMHG,ORVACUUMININHGLARGERUNITSAREUSUALLYRATEDONLYFORCONTINUOUSDUTY,BUTSMALLERUNITSMAYHAVEAHIGHERVACUUMRATINGFORINTERMITTENTDUTYINSMALLERUNITS,TEMPERATURERISECONSIDERATIONSLIMITTHEVACUUMTHATCANBEPRODUCEDCONTINUOUSANDINTERMITTENTVACUUMRATINGSAREDETERMINEDFORSTANDARDATMOSPHERICPRESSURE2992INHGLOWERAMBIENTPRESSURESREDUCETHEVACUUMTHATCANBEPRODUCEDTHERATINGISDETERMINEDFROMWHEREVAADJUSTEDVACUUMRATING,INHG;VOORIGINALVACUUMRATINGATSTANDARDCONDITIONS,INHG;ANDPAANTICIPATEDATMOSPHERICPRESSUREATTHEAPPLICATIONSITE,INHGRATEOFAIRREMOVALISTHESECONDCRITERIONVACUUMPUMPSAREFLOWRATEDACCORDINGTOTHEVOLUMEOFAIREXHAUSTEDWITHNOPRESSUREDIFFERENTIALACROSSTHEPUMPMANUFACTURERSPROVIDECURVESSHOWINGFREEAIRDELIVERYATRATEDSPEEDFORVACUUMLEVELSRANGINGFROM0INHGSOCALLEDOPENCAPACITYTOMAXIMUMVACUUMRATINGSOMEMANUFACTURERSALSOPROVIDECURVESOFCAPACITYATDIFFERENTSPEEDSFORAGIVENVACUUMTHELASTPUMPCRITERIONISPOWERREQUIREMENTCOMPAREDWITHAIRCOMPRESSORS,VACUUMPUMPSREQUIRERELATIVELYLITTLEPOWERATLOWFLOWS,VACUUMORPRESSUREDIFFERENTIALISHIGH;ATHIGHFLOWS,VACUUMISLOWTHEREFORE,POWER,WHICHISPROPORTIONALTOFLOWANDPRESSUREDIFFERENTIAL,ISGENERALLYLOWPOWEROUTPUTOFTHEPUMPCANBEFOUNDFROMPRESSUREFLOWCURVESPROVIDEDBYMANUFACTURERSINPUTPOWERANDSPEEDREQUIREMENTSAREALSOSHOWNINTHEDATAOVERALLPUMPEFFICIENCYINCLUDINGBOTHVOLUMETRICANDMECHANICALEFFICIENCYCANBEEVALUATEDBYCOMBININGTHISDATATHISISDONEBYDIVIDINGTHEFREEAIRCAPACITYOFTHEPUMPATTHEREQUIREDVACUUMLEVELBYDRIVEPOWERREQUIREDATTHATCONDITIONTHERESULTISPROPORTIONALTOTHEPRODUCTOFGAGEVACUUMANDAIRFLOWRATEANDISREPRESENTATIVEOFEFFICIENCYALLTHREEPERFORMANCECRITERIAVACUUM,FLOWANDPOWERCANBEAFFECTEDBYPUMPTEMPERATUREATHIGHERVACUUMLEVELS,LITTLEAIRFLOWSTHROUGHTHEPUMP,SOLITTLEHEATISTRANSFERREDTOTHEAIRMUCHOFTHEHEATGENERATEDBYFRICTIONMUSTBEDISSIPATEDBYTHEPUMPTHISHEATGRADUALLYRAISESPUMPTEMPERATUREANDCANDRASTICALLYREDUCESERVICELIFETEMPERATUREEXCURSIONSAREESPECIALLYIMPORTANTTOINTERMITTENTDUTYPUMP,WHICHCANOVERHEATIFONTIMEGREATLYEXCEEDSOFFTIMEVACUUMPUMPSARECLASSIFIEDASEITHERPOSITIVEORNONPOSITIVEDISPLACEMENTAPOSITIVEDISPLACEMENTPUMPCREATESVACUUMBYISOLATINGANDCOMPRESSINGADISTINCT,CONSTANTVOLUMEOFAIRTHECOMPRESSEDAIRISVENTEDOUTONEPORT,ANDAVACUUMISCREATEDATTHEOTHERPORTWHERETHEAIRISDRAWNINTHISGENERATESRELATIVELYHIGHVACUUM,BUTLITTLEFLOWANONPOSITIVEDISPLACEMENTPUMP,ONTHEOTHERHAND,USESROTATINGIMPELLERBLADESTOACCELERATEAIRANDCREATEAVACUUMATTHEINLETPORTWHILENONPOSITIVEDISPLACEMENTPUMPSCANNOTPRODUCEHIGHLEVELSOFVACUUM,THEYPROVIDEHIGHFLOWRATESPRINCIPALTYPESOFPOSITIVEDISPLACEMENTVACUUMPUMPSINCLUDEPISTON,DIAPHRAGM,ROCKINGPISTON,ROTARYVANE,LOBEDROTOR,ROTARYSCREW,ANDLIQUIDRINGDESIGNSRECIPROCATINGPISTONPUMPSGENERATERELATIVELYHIGHVACUUMSFROM27TOMORETHAN29INHGUNDERAVARIETYOFOPERATINGCONDITIONSTYPICALPUMPSOFTHISTYPEHAVEONEORMOREPISTONSLINKEDTOAROTATINGCRANKSHAFTTHEALTERNATINGPISTONACTIONMOVESAIRPASTCHECKVALVESINTHECYLINDERHEADTOCREATEAVACUUMATTHEINLETPORTLUBRICATEDPISTONPUMPSAREQUIETER,PRODUCELESSVIBRATION,HAVEAHIGHERCAPACITY,ANDFEATUREAMUCHLONGERLIFETHANOILLESSDESIGNS,BUTTHEYAREALSOHEAVIERANDMOREEXPENSIVEDIAPHRAGMPUMPSOFFERTHEADVANTAGEOFTHEFLUIDCHAMBERBEINGTOTALLYSEALEDFROMTHEPUMPINGMECHANISMSANECCENTRICCONNECTINGRODMECHANICALLYFLEXESADIAPHRAGMINSIDETHECLOSEDCHAMBERTOCREATEAVACUUMTHISRESULTSINSOMEWHATLOWERVACUUMCOMPAREDTOTHATPRODUCEDBYARECIPROCATINGPISTONHOWEVER,THEDIAPHRAGMSLOWERCOMPRESSIONRATIOLOWFLOW,LARGEDIAMETER,ANDSHORTSTROKEMAKESFORQUIET,ECONOMICAL,ANDRELIABLEOPERATIONTHEDESIGNISAVAILABLEINBOTHONEANDTWOSTAGEVERSIONSSINGLESTAGEPUMPSPROVIDEVACUUMUPTO255INHG,WHILETWOS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