英文摘要翻譯Populartypesofreciprocatingpumpsforfluid-powersystemincludetheradial-piston,axial-piston,duplex,andtriplexpumps.Probablythemostfamiliarreciprocatingpumpisthewell-knownfarmliftpump.Inthispumpthemovesthehandleupanddowntoproduceasimilarreciprocatingmotionofthepistoninthepumpcylinder.Thepistonslidesintheclose-fittingcylinderorbarrel.Duringthesuctionstrokeofthepiston.Duringthepistonupstroke,someairisremovedfromthepumpcylinder.Thisreducesthepressureinthecylindertolessthanthepressureofthesurroundingatmosphere.Atmosphericpressure,actingonthesurfaceoffluidinthereservoir,forcefluidupthesuctionpipeintothecylinder.Thepumpisthussaidtoproduceasuctiononthefluid.Note,however,thatitisthedifferenceinpressurebetweentheatmosphereandtheinteriorofthepumpcylinderthatproducetheupwardflowofthefluid.Attheinlettothepumpsuctionpipe,aball-typefootvalveisfitted.Thisvalveisasolidrubberormetalballthatallowsfluidtoenterduringthesuctionstrokebutpreventfluidfromleavingthepipewhenthepumpisidle.Asimilarvalveisfittedattheinlettothepumpcylinder.Thevalveinthecylinderistermedacheckvalvebecauseispreventfluidfromdrainingoutofthecylinder.Asimilarvalveismountedinthecenterofthehollowpump.Duringtheupstrokeofthepiston,thelowercheckvalveisliftedoffitsseatandthefluidabovethepistonseatsthevalveinthepiston.Fluidabovethepistonisdischargedoutthepumpspoutduringthisstroke.Whenthepistonreachesthetopofitsstroke,themovementstopsforamoment.Thenthepistonbeginsitsdownstroke.Duringthedownwardtravel,thepistoncheckvalveisliftedoffitsseatbythefluidtrappedinthecylinder.Pressureonthefluidtrappedinthecylindercausethecylindercheckvalvetoclose.Thispreventsfluidfromleavingthecylinder.Whilethepistonmovesdownward,thefluidmovesfromunderthepistontoabovethepiston.Thus,thepumpispreparedforitsnextdischargesstroke.Notethatfluidisdischargedbythispumponlyduringtheupstroke.Sincethepumpdischargesduringonlyoneofitstwostrokes,thepumpistermedsingle-acting.Areciprocatingpumpthatdischargesduringbothitsstrokesistermeddouble-acting.Sinceadouble-actingpumpdischargesduringbothstrokes,ithasabouttwicethecapacityofasingle-actingpump.Thereisatypicalhand-operatedreciprocatingpumpusedasanauxiliarypowersourceinfluid-powersystem.Movementofthehandlefromlefttorightproduceacorrespondingmotionofthepiston.Duringmovementofthepistontotheright,pressureexertonthefluidbythepistonforcesdischargevalveDoffitsseat.SuctionvalveSisforceontoitsseat,preventingdischargeoffluidtothereservoir.WhilevalveDisoffitseat,fluidisdischargedouttheright-handsideofthepump.Duringthissamestroke,suctionvalveS1liftedoffitsseatandfluidissuckedintotheleft-handchamberofthepump.Whenthedirectionofthepistontravelisreversedsothatthepistontravelsfromrighttoleft.ValveDisclosedbyitsspring.ValveD1isopenedbytheincreasedpressure,whilevalveS1isclosedbythepressureincrease.SuctionvalveSisopened,andthepistondrawsfluidintotheright-handchamberwhiledischargingfromtheleft-handone.Thepumpisdouble-actingbecauseitdischargesfluidoneachstroke.Allpistonsoperateontheprinciplethatapistonreciprocatinginaborewilldrawinfluidasitisretractedandexpelitontheforwardstroke.Twobasicdesignsareradialandaxial；bothareavailableasfixedorvariabledisplacementmodels.Aradialpumphasthepistonarrangedradicallyinacylinderblockwhileinaxialunitsthepistonsareparalleltoeachotherandtotheaxisofthecylinderblock.Thelattermaybefurtherdividedintoin-line(swashplateorwobbleplate)andbentaxistype.Inaradialpumpthecylinderblockrotatesonsstationarypimpleandinsideacircularreactionringorrotor.Astheblockrotatescentrifugalforce,chargingpressureorsomeformofmechanicalactioncausethepistontofollowtheinnersurfaceoftheringwhichisoffsetfromthecenterlineofthecylinderblock.Asthepistonreciprocateintheirbores,portinginthepimplepermitsthemtotakeinfluidastheymoveoutwardanddischargeitastheymovein.Thesizeandnumberofpistons(theremaybemorethanonebankinasinglecylinderblock)and,ofcoursethelengthoftheirstrokedeterminespumpdisplacement.Insomemodelsthedisplacementcanbevariedbymovingthereactionringtoincreaseordecreasepistontravel.Externalcontrolsofseveraltypesareavailableforthispurpose.Inaxialpistonpump,thecylinderblockanddrivershaftareonthesamecenterlineandthepistonsreciprocateparalleltothedriveshaft.Thesimplesttypeofaxialpistonpumpistheswashplateinlinedesign.Thecylinderblockinthispumpisturnedbythedriveshaft.Pistonsfittedtoboresinthecylinderareconnectedthroughpistonshoesandaretractingring,sothattheshoesbearagainstanangledswashplate.Astheblockturns,thepistonshoesfollowtheswashplate,causingthepistontoreciprocate.Theportsarearrangedinthevalveplatesothatthepistontheinletastheyarebeingpulledoutandpasstheoutletastheyarebeingforcebackin.Inthesepumpsthedisplacementisalsodeterminedbythesizeandnumberofpistonsaswellastheirstrokelength,thelatterbeingafunctionoftheswashplateangle.Invariabledisplacementmodestofthechangestheswashplateisinstalledinamoveableyoke“Pivoting”theyokeonpointlesschangestheswashplateangletoincreaseordecreasethepistonstroke.Theyyokecanbepositionedmanually,withaservocontrol.Maximumangleontheunitshownislimitedto17.5degreesbyconstruction.Operationoftheinlinepumpcompensatorcontrolisshownschematically.Thecontrolconsistsofscompensatorvalvebalancedbetweenloadpressureandtheforceofaspring,apistoncontrolledbythevalvetomovetheyoke,andayokereturnspring.Withnooutletpress,theyokereturnspringmovestheyoketothefulldeliveryposition.Aspressurebuildsup,itactsagainsttheendofthevalvespool.Whenthepressureishighenoughtoovercomethevalvespring,thespoolisdisplaceandoilenterstheyokepiston.Thepistonisforcedbytheoilunderpressuretodecreasethepumpcase,andthespringreturnstheyoketosgreaterangle.Thecompensatorthusadjuststhepumpoutputtowhateverisrequiredtodevelopandmaintainthepresetpressure.Thispreventsexcesspowerlossbyavoidingreliefvalveoperationatfullpumpvolumeduringholdingorclamping.Avariationoftheinlinepistonisthewobbleplatepump.Inawobbleplatepump,thecylinderisstationaryandcantedplateisturnedbythedriveshaft.Astheplateturns,it“wobbles”andpushesagainstspring-loadedpistonstoforcethemtoreciprocate.Separateinletandoutletcheckvalvesarerequiredasinareciprocatingpump,becausethecylinderdonotmovepasttheport.Inabentaxispistonpump,thecylinderblockturnswiththedriveshaft,butatanoffsetangle.Thepistonrodsareattachedtothedriveshaftflangebyballjoints,andareforcedinandoutoftheirboresasthedistancebetweenthedriveshaftflangeandcylinderblockchanges.Auniversallinkkeysthecylinderblocktothedriveshafttomaintainalignmentandassurethattheyturntogether.Thelinkdoesnottransmitforceexcepttoaccelerateanddeceleratethecylinderblockandtoovercomeresistanceoftheblockrevolvingintheoilfilledhousing.Thedisplacementofthispumpvarieswiththeoffsetangle,themaximumanglebeing30degrees,theminimumzero.Fixeddisplacementmodelsareusuallyavailablewith23-degreeor30-degreeangles.Inthevariabledisplacementconstructionsyokewithanexternalcontrolisusedtochangetheangle.Withsomecontrols,theyokecanbemovedovercentertoreversethedirectionofflowfromthepump.Variousmethodsareusedtocontroldisplacementofvariabledisplacementbent-axispump.Typicalcontrolsarethehandwheel,pressurecompensator,andservo.ItshowsspressurecompensatorcontrolforaPVA120bent-axispump.Inview,thesystempressureissufficienttoovercomethespringforceisthecompensator.Assresult,thespoolliftsallowingfluidtoflowintothestrokingcylinder.Althoughtheholdingcylinderalsohassystempressureapplied,theareaofthestrokingcylinderpistonismuchgreatersotheforcedevelopedmovestheyokeuptodecreaseflow.Theyokemovesdownassystempressuredropsbelowthatrequiredtoovercomethecompensatorspringforce.AhandwheelcontrolforthePVA120pumpisveryeasy.Theadjustingscrewismov