机械外文翻译外文文献英文文献液压机械及泵.docx

机械外文翻译外文文献英文文献液压机械及泵.docx

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机械外文翻译外文文献英文文献液压机械及泵

Hydraulicmachineryandpump

Hydraulicmachineryaremachinesandtoolswhichusefluidpowertodowork.Heavyequipmentisacommonexample.

Inthistypeofmachine,high-pressureliquid-calledhydraulicfluid-istransmittedthroughoutthemachinetovarioushydraulicmotorsandhydrauliccylinders.Thefluidiscontrolleddirectlyorautomaticallybycontrolvalvesanddistributedthroughhosesandtubes.

Thepopularityofhydraulicmachineryisduetotheverylargeamountofpowerthatcanbetransferredthroughsmalltubesandflexiblehoses,andthehighpowerdensityandwidearrayofactuatorsthatcanmakeuseofthispower.

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

Hydrauliccircuits

Forthehydraulicfluidtodowork,itmustflowtotheactuatorandormotors,thenreturntoareservoir.

Thefluidisthenfilteredandre-pumped.Thepathtakenbyhydraulicfluidiscalledahydrauliccircuitofwhichthereareseveraltypes.Opencentercircuitsusepumpswhichsupplya

continuousflow.Theflowisreturnedtotankthroughthecontrolvalve'sopencenter;thatis,whenthecontrolvalveiscentered,itprovidesanopenreturnpathtotankandthefluidisnotpumpedtoahighpressure.Otherwise,ifthecontrolvalveisactuateditroutesfluidtoandfromanactuatorandtank.Thefluid'spressurewillrisetomeetanyresistanee,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,butprovideIongerlifeoperatingathigherpressure,withdifficultfluidsandIongercontinuousdutycycles.Pistonpumpsmakeuponehalfofahydrostatictransmission.

Controlvalves

Directionalcontrolvalvesroutethefluidtothedesiredactuator.

Theyusuallyconsistofaspoolinsideacastironorsteelhousing.

Directionalcontrolvalvesareusuallydesignedtobestackable,withonevalveforeachhydrauliccylinder,andonefluidinputsupplyingallthevalvesinthestack.

Thespoolpositionmaybeactuatedbymechanicallevers,hydraulicpilotpressure,orsolenoidswhichpushthespoolleftorright.

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

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

Pressurereducingvalvesreducethesupplypressureasneededforvariouscircuits.

Checkvalvesareone-wayvalves,allowinganaccumulatortochargeandmaintainitspressureafterthemachineisturnedoff,forexample.

Counterbalaneevalvesareinfactaspecialtypeofpilotcontrolledcheckvalve.Whereasthecheckvalveisopenorclosed,thecounterbalancevalveactsabitlikeapilotcontrolledflowcontrol.

Hydraulicpumptypes

Gearpumps

Gearpumps（withexternalteeth）（fixeddisplacement）aresimple

andeconomicalpumps.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（engineerHans

Thoma,Germany,patent1935）withmax25degreesangleandtheWahlmark-principle（GunnarAxelWahlmark,patent1960）with

spherical-shapedpistonsinonepiecewiththepistonrod,pistonrings,andmaximum40degreesbetweenthedriveshaftcenterlineandpistons（VolvoHydraulicsCo.）.Thesehavethebestefficiencyofallpumps.Althoughingeneralthelargestdisplacementsareapproximatelyonelitreperrevolution,ifnecessaryatwo-litersweptvolumepumpcanbebuilt.Oftenvariable-displacementpumpsareused,sothattheoilflowcanbeadjustedcarefully.Thesepumpscaningeneralworkwithaworkingpressureofupto350—420barsincontinuouswork.

Axialpistonpumpsswashplateprinciple

（fixedand

Axialpistonpumpsusingtheswashplateprincipleadjustabledisplacement）haveaqualitythatisalmostthesameasthebentaxismodel.Theyhavetheadvantageofbeingmorecompactindesign.Thepumpsareeasierandmoreeconomicaltomanufacture;thedisadvantageisthattheyaremoresensitivetooilcontamination.

Radialpistonpumps

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

Peristalticpumps

Peristalticpui

arenotgenerallyusedforhighpressures.

Pumpsforopenandclosedsystems

Mostpumpsareworkinginopensystems.Thepumpdrawsoilfromareservoiratatmosphericpressure.Itisveryimportantthatthereisnocavitationatthesuctionsideofthepump.Forthisreasontheconnectionofthesuctionsideofthepumpislargerindiameterthantheconnectionofthepressureside.Incaseoftheuseofmulti-pumpassemblies,thesuctionconnectionofthepumpisoftencombined.Itispreferredtohavefreeflowtothepump

（pressureatinletofpumpatleast0.8bars）.Thebodyofthepump

isofteninopenconnectionwiththesuctionsideofthepump.

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-