液压机械与液压泵外文翻译文献Word格式.docx

液压机械与液压泵外文翻译文献Word格式.docx

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Thepopularityofhydraulicmachineryisduetotheverylargeamountofpowerthatcanbetransferredthroughsmalltubesandflexiblehoses,andthehighpowerdensityandwidearrayofactuatorsthatcanmakeuseofthispower.

Hydraulicmachineryisoperatedbytheuseofhydraulics,wherealiquidisthepoweringmedium.Pneumatics,ontheotherside,isbasedontheuseofagasasthemediumforpowertransmission,generationandcontrol.

Hydrauliccircuits

Forthehydraulicfluidtodowork,itmustflowtotheactuatorandormotors,thenreturntoareservoir.

Thefluidisthenfilteredandre-pumped.Thepathtakenbyhydraulicfluidiscalledahydrauliccircuitofwhichthereareseveraltypes.Opencentercircuitsusepumpswhichsupplyacontinuousflow.Theflowisreturnedtotankthroughthecontrolvalve'

sopencenter;

thatis,whenthecontrolvalveiscentered,itprovidesanopenreturnpathtotankandthefluidisnotpumpedtoahighpressure.Otherwise,ifthecontrolvalveisactuateditroutesfluidtoandfromanactuatorandtank.Thefluid'

spressurewillrisetomeetanyresistance,sincethepumphasaconstantoutput.Ifthepressurerisestoohigh,fluidreturnstotankthroughapressurereliefvalve.

Hydraulicpumpssupplyfluidtothecomponentsinthesystem.Pressureinthesystemdevelopsinreactiontotheload.Hence,apumpratedfor5,000psiiscapableofmaintainingflowagainstaloadof5,000psi.Pumpshaveapowerdensityabouttentimesgreaterthananelectricmotor（byvolume）.Theyarepoweredbyanelectricmotororanengine,connectedthroughgears,belts,oraflexibleelastomericcouplingtoreducevibration.

Commontypesofhydraulicpumpstohydraulicmachineryapplicationsare;

Gearpump:

cheap,durable,simple.Lessefficient,becausetheyareconstantdisplacement,andmainlysuitableforpressuresbelow20MPa（3000psi）.

Vanepump:

cheapandsimple,reliable（especiallying-rotorform）.Goodforhigher-flowlow-pressureoutput.

Axialpistonpump:

manydesignedwithavariabledisplacementmechanism,tovaryoutputflowforautomaticcontrolofpressure.Therearevariousaxialpistonpumpdesigns,includingswashplateandcheckball.Themostcommonistheswashplatepump.Radialpistonpump:

Apumpthatisnormallyusedforveryhighpressureatsmallflows.

Pistonpumpsaremoreexpensivethangearorvanepumps,butprovidelongerlifeoperatingathigherpressure,withdifficultfluidsandlongercontinuousdutycycles.Pistonpumpsmakeuponehalfofahydrostatictransmission.

Controlvalves

Directionalcontrolvalvesroutethefluidtothedesiredactuator.Theyusuallyconsistofaspoolinsideacastironorsteelhousing.

Directionalcontrolvalvesareusuallydesignedtobestackable,withonevalveforeachhydrauliccylinder,andonefluidinputsupplyingallthevalvesinthestack.

Thespoolpositionmaybeactuatedbymechanicallevers,hydraulicpilotpressure,orsolenoidswhichpushthespoolleftorright.

Themainvalveblockisusuallyastackofofftheshelfdirectionalcontrolvalveschosenbyflowcapacityandperformance.Somevalvesaredesignedtobeproportional（flowrateproportionaltovalveposition）,whileothersmaybesimplyon-off.Thecontrolvalveisoneofthemostexpensiveandsensitivepartsofahydrauliccircuit.

Pressurereliefvalvesareusedinseveralplacesinhydraulicmachinery;

onthereturncircuittomaintainasmallamountofpressureforbrakes,pilotlines,etc...Onhydrauliccylinders,topreventoverloadingandhydrauliclinerupture.Onthehydraulicreservoir,tomaintainasmallpositivepressurewhichexcludesmoistureandcontamination.

Pressurereducingvalvesreducethesupplypressureasneededforvariouscircuits.

Checkvalvesareone-wayvalves,allowinganaccumulatortochargeandmaintainitspressureafterthemachineisturnedoff,forexample.

Counterbalancevalvesareinfactaspecialtypeofpilotcontrolledcheckvalve.Whereasthecheckvalveisopenorclosed,thecounterbalancevalveactsabitlikeapilotcontrolledflowcontrol.

Hydraulicpumptypes

Gearpumps

Gearpumps（withexternalteeth）（fixeddisplacement）aresimpleandeconomicalpumps.Thesweptvolumeordisplacementofgearpumpsforhydraulicswillbebetweenabout1cm3（0.001litre）and200cm3（0.2litre）.Thesepumpscreatepressurethroughthemeshingofthegearteeth,whichforcesfluidaroundthegearstopressurizetheoutletside.Somegearpumpscanbequitenoisy,comparedtoothertypes,butmoderngearpumpsarehighlyreliableandmuchquieterthanoldermodels.

Rotaryvanepumps

Rotaryvanepumps（fixedandsimpleadjustabledisplacement）havehigherefficienciesthangearpumps,butarealsousedformidpressuresupto180barsingeneral.Sometypesofvanepumpscanchangethecentreofthevanebody,sothatasimpleadjustablepumpisobtained.Theseadjustablevanepumpsareingeneralconstantpressureorconstantpowerpumps:

thedisplacementisincreaseduntiltherequiredpressureorpowerisreachedandsubsequentlythedisplacementorsweptvolumeisdecreaseduntilanequilibriumisreached.

Screwpumps

Screwpumps（fixeddisplacement）areadoubleArchimedes'

screw,butclosed.Thismeansthattwoscrewsareusedinonebody.Thepumpsareusedforhighflowsandrelativelylowpressure（max100bar）.Theywereusedonboardshipswheretheconstantpressurehydraulicsystemwasgoingthroughthewholeship,especiallyforthecontrolofballvalves,butalsoforthesteeringgearandhelpdrivesystems.Theadvantageofthescrewpumpsisthelowsoundlevelofthesepumps;

theefficiencyisnotthathigh.

Bentaxispumps

Bentaxispumps,axialpistonpumpsandmotorsusingthebentaxisprinciple,fixedoradjustabledisplacement,existsintwodifferentbasicdesigns.TheThoma-principle（engineerHansThoma,Germany,patent1935）withmax25degreesangleandtheWahlmark-principle（GunnarAxelWahlmark,patent1960）withspherical-shapedpistonsinonepiecewiththepistonrod,pistonrings,andmaximum40degreesbetweenthedriveshaftcenterlineandpistons（VolvoHydraulicsCo.）.Thesehavethebestefficiencyofallpumps.Althoughingeneralthelargestdisplacementsareapproximatelyonelitreperrevolution,ifnecessaryatwo-litersweptvolumepumpcanbebuilt.Oftenvariable-displacementpumpsareused,sothattheoilflowcanbeadjustedcarefully.Thesepumpscaningeneralworkwithaworkingpressureofupto350–420barsincontinuouswork.

Axialpistonpumpsswashplateprinciple

Axialpistonpumpsusingtheswashplateprinciple（fixedandadjustabledisplacement）haveaqualitythatisalmostthesameasthebentaxismodel.Theyhavetheadvantageofbeingmorecompactindesign.Thepumpsareeasierandmoreeconomicaltomanufacture;

thedisadvantageisthattheyaremoresensitivetooilcontamination.

Radialpistonpumps

Radialpistonpumps（fixeddisplacement）areusedespeciallyforhighpressureandrelativelysmallflows.Pressuresofupto650bararenormal.Infactvariabledisplacementisnotpossible,butsometimesthepumpisdesignedinsuchawaythattheplungerscanbeswitchedoffonebyone,sothatasortofvariabledisplacementpumpisobtained.

Peristalticpumps

Peristalticpumpsarenotgenerallyusedforhighpressures.

Pumpsforopenandclosedsystems

Mostpumpsareworkinginopensystems.Thepumpdrawsoilfromareservoiratatmosphericpressure.Itisveryimportantthatthereisnocavitationatthesuctionsideofthepump.Forthisreasontheconnectionofthesuctionsideofthepumpislargerindiameterthantheconnectionofthepressureside.Incaseoftheuseofmulti-pumpassemblies,thesuctionconnectionofthepumpisoftencombined.Itispreferredtohavefreeflowtothepump（pressureatinletofpumpatleast0.8bars）.Thebodyofthepumpisofteninopenconnectionwiththesuctionsideofthepump.

Incaseofaclosedsystem,bothsidesofthepumpcanbeathighpressure.Thereservoirisoftenpressurizedwith6-20barsboostpressure.Forclosedloopsystems,normallyaxialpistonpumpsareused.Becausebothsidesarepressurized,thebodyofthepumpneedsaseparateleakageconnection.

Multipumpassembly

Inahydraulicinstallation,onepumpcanservemorecylindersandmotors.Theproblemhoweveristhatinthatcaseaconstantpressuresystemisrequiredandthesystemalwaysneedsthefullpower.Itismoreeconomictogiveeachcylinderandmotoritsownpump.Inthatcasemultipumpassembliescanbeused.Gearpumpscanoftenbeobtainedasmultipumps.Thedifferentchambers（sometimesofdifferentsize）aremountedinonebodyorbuilttogether.Alsovanepumpscanoftenbeobtainedasamultipump.Gerotorpumpsareoftensuppliedasmultipumps.Screwpumpscanbebuilttogetherwithagearpumporavanepump.Axialpistonswashplatepumpscanbebuilttogetherwithasecondpumpofthesameorsmallersize,orcanbebuilttogetherwithoneormoregearpumpsorvanepumps（dependingonthesupplier）.Axialplungerpumpsofthebentaxisdesigncannotbebuilttogetherwithotherpumps.

翻译：

液压机械及泵

液压机械是机械和工具,它使用流体的力量去做的工作。

重型设备是一种常见的例子。

在这种类型的机器，高压液-所谓的液压油-是整个传送机各种液压马达和液压缸。

流体是直接控制或自动通过控制阀，并通过软管和管分配。

液压机械的普及是由于应用非常的大量，可以通过小管和软管转移，高