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外文翻译--泵及其相关附件.doc

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外文翻译--泵及其相关附件.doc

英文摘要翻译Populartypesofreciprocatingpumpsforfluidpowersystemincludetheradialpiston,axialpiston,duplex,andtriplexpumps.Probablythemostfamiliarreciprocatingpumpisthewellknownfarmliftpump.Inthispumpthemovesthehandleupanddowntoproduceasimilarreciprocatingmotionofthepistoninthepumpcylinder.Thepistonslidesintheclosefittingcylinderorbarrel.Duringthesuctionstrokeofthepiston.Duringthepistonupstroke,someairisremovedfromthepumpcylinder.Thisreducesthepressureinthecylindertolessthanthepressureofthesurroundingatmosphere.Atmosphericpressure,actingonthesurfaceoffluidinthereservoir,forcefluidupthesuctionpipeintothecylinder.Thepumpisthussaidtoproduceasuctiononthefluid.Note,however,thatitisthedifferenceinpressurebetweentheatmosphereandtheinteriorofthepumpcylinderthatproducetheupwardflowofthefluid.Attheinlettothepumpsuctionpipe,aballtypefootvalveisfitted.Thisvalveisasolidrubberormetalballthatallowsfluidtoenterduringthesuctionstrokebutpreventfluidfromleavingthepipewhenthepumpisidle.Asimilarvalveisfittedattheinlettothepumpcylinder.Thevalveinthecylinderistermedacheckvalvebecauseispreventfluidfromdrainingoutofthecylinder.Asimilarvalveismountedinthecenterofthehollowpump.Duringtheupstrokeofthepiston,thelowercheckvalveisliftedoffitsseatandthefluidabovethepistonseatsthevalveinthepiston.Fluidabovethepistonisdischargedoutthepumpspoutduringthisstroke.Whenthepistonreachesthetopofitsstroke,themovementstopsforamoment.Thenthepistonbeginsitsdownstroke.Duringthedownwardtravel,thepistoncheckvalveisliftedoffitsseatbythefluidtrappedinthecylinder.Pressureonthefluidtrappedinthecylindercausethecylindercheckvalvetoclose.Thispreventsfluidfromleavingthecylinder.Whilethepistonmovesdownward,thefluidmovesfromunderthepistontoabovethepiston.Thus,thepumpispreparedforitsnextdischargesstroke.Notethatfluidisdischargedbythispumponlyduringtheupstroke.Sincethepumpdischargesduringonlyoneofitstwostrokes,thepumpistermedsingleacting.Areciprocatingpumpthatdischargesduringbothitsstrokesistermeddoubleacting.Sinceadoubleactingpumpdischargesduringbothstrokes,ithasabouttwicethecapacityofasingleactingpump.Thereisatypicalhandoperatedreciprocatingpumpusedasanauxiliarypowersourceinfluidpowersystem.Movementofthehandlefromlefttorightproduceacorrespondingmotionofthepiston.Duringmovementofthepistontotheright,pressureexertonthefluidbythepistonforcesdischargevalveDoffitsseat.SuctionvalveSisforceontoitsseat,preventingdischargeoffluidtothereservoir.WhilevalveDisoffitseat,fluidisdischargedouttherighthandsideofthepump.Duringthissamestroke,suctionvalveS1liftedoffitsseatandfluidissuckedintothelefthandchamberofthepump.Whenthedirectionofthepistontravelisreversedsothatthepistontravelsfromrighttoleft.ValveDisclosedbyitsspring.ValveD1isopenedbytheincreasedpressure,whilevalveS1isclosedbythepressureincrease.SuctionvalveSisopened,andthepistondrawsfluidintotherighthandchamberwhiledischargingfromthelefthandone.Thepumpisdoubleactingbecauseitdischargesfluidoneachstroke.Allpistonsoperateontheprinciplethatapistonreciprocatinginaborewilldrawinfluidasitisretractedandexpelitontheforwardstroke.Twobasicdesignsareradialandaxialbothareavailableasfixedorvariabledisplacementmodels.Aradialpumphasthepistonarrangedradicallyinacylinderblockwhileinaxialunitsthepistonsareparalleltoeachotherandtotheaxisofthecylinderblock.Thelattermaybefurtherdividedintoinlineswashplateorwobbleplateandbentaxistype.Inaradialpumpthecylinderblockrotatesonsstationarypimpleandinsideacircularreactionringorrotor.Astheblockrotatescentrifugalforce,chargingpressureorsomeformofmechanicalactioncausethepistontofollowtheinnersurfaceoftheringwhichisoffsetfromthecenterlineofthecylinderblock.Asthepistonreciprocateintheirbores,portinginthepimplepermitsthemtotakeinfluidastheymoveoutwardanddischargeitastheymovein.Thesizeandnumberofpistonstheremaybemorethanonebankinasinglecylinderblockand,ofcoursethelengthoftheirstrokedeterminespumpdisplacement.Insomemodelsthedisplacementcanbevariedbymovingthereactionringtoincreaseordecreasepistontravel.Externalcontrolsofseveraltypesareavailableforthispurpose.Inaxialpistonpump,thecylinderblockanddrivershaftareonthesamecenterlineandthepistonsreciprocateparalleltothedriveshaft.Thesimplesttypeofaxialpistonpumpistheswashplateinlinedesign.Thecylinderblockinthispumpisturnedbythedriveshaft.Pistonsfittedtoboresinthecylinderareconnectedthroughpistonshoesandaretractingring,sothattheshoesbearagainstanangledswashplate.Astheblockturns,thepistonshoesfollowtheswashplate,causingthepistontoreciprocate.Theportsarearrangedinthevalveplatesothatthepistontheinletastheyarebeingpulledoutandpasstheoutletastheyarebeingforcebackin.Inthesepumpsthedisplacementisalsodeterminedbythesizeandnumberofpistonsaswellastheirstrokelength,thelatterbeingafunctionoftheswashplateangle.InvariabledisplacementmodestofthechangestheswashplateisinstalledinamoveableyokePivotingtheyokeonpointlesschangestheswashplateangletoincreaseordecreasethepistonstroke.Theyyokecanbepositionedmanually,withaservocontrol.Maximumangleontheunitshownislimitedto17.5degreesbyconstruction.Operationoftheinlinepumpcompensatorcontrolisshownschematically.Thecontrolconsistsofscompensatorvalvebalancedbetweenloadpressureandtheforceofaspring,apistoncontrolledbythevalvetomovetheyoke,andayokereturnspring.Withnooutletpress,theyokereturnspringmovestheyoketothefulldeliveryposition.Aspressurebuildsup,itactsagainsttheendofthevalvespool.Whenthepressureishighenoughtoovercomethevalvespring,thespoolisdisplaceandoilenterstheyokepiston.Thepistonisforcedbytheoilunderpressuretodecreasethepumpcase,andthespringreturnstheyoketosgreaterangle.Thecompensatorthusadjuststhepumpoutputtowhateverisrequiredtodevelopandmaintainthepresetpressure.Thispreventsexcesspowerlossbyavoidingreliefvalveoperationatfullpumpvolumeduringholdingorclamping.Avariationoftheinlinepistonisthewobbleplatepump.Inawobbleplatepump,thecylinderisstationaryandcantedplateisturnedbythedriveshaft.Astheplateturns,itwobblesandpushesagainstspringloadedpistonstoforcethemtoreciprocate.Separateinletandoutletcheckvalvesarerequiredasinareciprocatingpump,becausethecylinderdonotmovepasttheport.Inabentaxispistonpump,thecylinderblockturnswiththedriveshaft,butatanoffsetangle.Thepistonrodsareattachedtothedriveshaftflangebyballjoints,andareforcedinandoutoftheirboresasthedistancebetweenthedriveshaftflangeandcylinderblockchanges.Auniversallinkkeysthecylinderblocktothedriveshafttomaintainalignmentandassurethattheyturntogether.Thelinkdoesnottransmitforceexcepttoaccelerateanddeceleratethecylinderblockandtoovercomeresistanceoftheblockrevolvingintheoilfilledhousing.Thedisplacementofthispumpvarieswiththeoffsetangle,themaximumanglebeing30degrees,theminimumzero.Fixeddisplacementmodelsareusuallyavailablewith23degreeor30degreeangles.Inthevariabledisplacementconstructionsyokewithanexternalcontrolisusedtochangetheangle.Withsomecontrols,theyokecanbemovedovercentertoreversethedirectionofflowfromthepump.Variousmethodsareusedtocontroldisplacementofvariabledisplacementbentaxispump.Typicalcontrolsarethehandwheel,pressurecompensator,andservo.ItshowsspressurecompensatorcontrolforaPVA120bentaxispump.Inview,thesystempressureissufficienttoovercomethespringforceisthecompensator.Assresult,thespoolliftsallowingfluidtoflowintothestrokingcylinder.Althoughtheholdingcylinderalsohassystempressureapplied,theareaofthestrokingcylinderpistonismuchgreatersotheforcedevelopedmovestheyokeuptodecreaseflow.Theyokemovesdownassystempressuredropsbelowthatrequiredtoovercomethecompensatorspringforce.AhandwheelcontrolforthePVA120pumpisveryeasy.Theadjustingscrewismovedinorouttovarythepumpflow.Pistonpumpsarehighlyefficientunitsavailableinawiderangeofcapacitiesfromverysmalltohigh.Mostarecapableofoperatinginthemediumtohighpressurerangewithothersgoingmuchhigher.Beingvariableandreversibletheylendthemselvesverywelltowelllargepressapplicationsandhydrostaticdrives.Becauseoftheircloselyfittedpartsandfinelymachinedsurfaces,cleanlinessandgoodqualityfluidsarevitaltolongservicelife.Frequently,hydraulicdesignerschooseofftheshelfpumpswithlittleconcernotherthansupplyingsufficientflowatavailableinputpower.Earlyemphasisthatpositivedisplacementpumpssupplyonlyflowandthatpressureisdevelopedbythesystemsuggestthat,asaminimum,thedynamicrelationshipbetweensystemandpumpshouldbeinvestigated.Intruth,thepumpshouldbechoseninlightofseveraloverallrequirementsandwithsystemdetailedandthenatureworkingfluidwellinmind.

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