机械专业文献翻译液压系统.docx

机械专业文献翻译液压系统.docx

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机械专业文献翻译液压系统

附录

英文原文：

HYDRAULICSYSTEM

Hydraulicsystemsarepower-transmittingassembliesemployingpressurizedliquidtotransmitenergyfromanenergy-generatingsourcetoanenergy-usearea.AllhydraulicsystemsdependonPascal’slaw,namedafterBlaisePascal,whodiscoveredthelaw.Thislawstatesthatpressurizedfluidwithinaclosedcontainer-suchascylinderorpipe-exertsequalforceonallofthesurfacesofthecontainer.

Inactualhydraulicsystems,Pascal’slawdefinesthebasisoftheresultswhichareobtainedfromthesystem.Thus,apumpmovestheliquidinthesystem.Theintakeofthepumpsconnectedtoaliquidsource,usuallycalledthetankorreservoir.Atmosphericpressure,pressingontheliquidinthereservoir,forcestheliquidintothepump.Whenthepumpoperates,itforcesliquidfromthetankintothedischargepipeatasuitablepressure.

Theflowofthepressurizedliquiddischargedbythepumpiscontrolledbyvalves.Threecontrolfunctionsareusedinmosthydraulicsystems:

（1）controloftheliquidpressure,

（2）controloftheliquidflowrate,and（3）controlofthedirectionofflowoftheliquid.

Theliquiddischargedbythepumpinafluid-powersystemisdirectedbyvalvestoahydraulicmotor.Ahydraulicmotordevelopsrotaryforceandmotion,usingthepressurizedliquidasitsenergysource.Manyhydraulicmotorsaresimilartopumps,exceptthatthemotoroperatesinareversemannerfromapump.

Wherelinearinsteadofrotarymotionisdesired,acylindricaltubefittedwithamovablepiston,calledahydrauliccylinder,isoftenused.Whenthepistonismovedbythepressurizedfluid,thepistonrodimpartsaforceormovesanobjectthroughadesireddistance.

Restrictingthemovementofthepistoninahydrauliccylinder,aswhenthepistoncarriesaload,createsaspecificpressurerelationshipwithinthecylinder.Thesurfaceareaofthepistonfaceissaidtocontainaspecificnumberofsquareinches.Thepressureofthepressurizedliquid,multipliedbythepitonarea,producesanoutputforce,measuredinpound,attheendofthepistonrod.

Thespeedofmovementofthepistonroddependsonhowfastthepressurizedfluidentersthecylinder.Flowintothecylindercanbedirectedtoeitherend,producingeitherapushingorpullingforceatthepistonrodend.Asealaroundtherodwhereitpassesthroughthecylinderendpreventsleakageoftheliquid.

Directionalcontrolofthepistondependsonwhichendofcylindertheliquidenters.Aspressurizedliquidentersoneendofthecylinder,liquidmustbedrainedfromtheotherend.Thedrainedliquidisledbacktothereservoir.Inapneumaticsystemusingair,theairintheexhaustingendofthecylinderisventedtotheatmosphere.

Directional-controlvalves,alsocalledtwo-way,three-way,four-way,etc.,arenamedinaccordancewiththeirbasicfunction.Pressure-controlandsimplerestrictorvalvesareusuallytwo-wayvalves.TheyprovideONorOFFservice.Athree-wayvalvesmayperformseveralfunctions,allassociatedwiththethree-portsinthevalve.Forexample,thepowerorpressurizedliquidfromapumpinatractormaybesenttothehydraulicsystemservingthetractor’sfront-endloader.Orthethree-wayvalvemaysendthepressurizedliquidtoahydraulicmotordrivingafeedconveyorwhilethefront-endloaderisnotbeingused.

Three-wayvalvesmayalsobeusedtodirectpressurizedfluidtoasingle-actinghydrauliccylinder.Asthethree-wayvalveisactuated（operated）itcanstopthepressurizedflowtothecylinder.Further,thesamevalvecandivertliquidfromthecylindertothereservoir,sothecylindercanretractbygravityorreturnspringsandassumeitsoriginalposition.

Afour-wayvalvehasfourportsoropenings.Thepressureportdirectsfluidflowtoanareawherepressurizedliquidisdesired.Oneoftheotherportscansimultaneouslydrainliquidfromapressurizedarea.Thedramliquidcanbedirectedtothereservoir.

Inafluid-powersystem,themovementofpressurizedfluidresemblestheactionofelectriccurrentinanelectricalsystem.Insuchasystem,electricalenergyiscontinuallymovingwhenworkisbeingdone.Thesameistrueofafluid-powersystem.

Inadirect-currentelectricalsystem,thespeedofadeviceisvariedbychangingtheflowofcurrenttothedevice.Alternating-currentsystem,usephaseshiftingtoattainsimilarspeedcontrol.Hydraulicsystemcanobtaininfinitespeedvariationsbyseveralmethodsofcontrol,Pneumaticsystems,becauseofthespringinessofthegas,haverelativelycrudespeedcontrol.

Influid-powersystems,thepumpcanbedesignedsothedischargeflowofthepressurizedliquidcanbevariedbymanipulatingthepumpmechanism,givingvaryingspeedsofthehydraulicmotororotheroutputdevice.Arestrictionunthepumpoutletcanlimitthefluidinamannersimilartothatusedinadirect-currentelectricalsystem.Wheredesired,hydraulicsystemscanbedesignedtousevalveswhichdivertflowtodifferentflowchannelstogivethedesiredspeedcontrol.

Thecompressibilityofhydraulicfluidisslight.But,ifdesired,thisslightcompressibilitycanbeusedtoabsorbsmall,erraticmachinemovementswhichcausepressurevariationsinafluid-powersystem.Pneumaticsystemshavethiscapabilityinherentlybecauseofthespringinessoftheairorgasusedinthesystem.Hydraulicsystemsmayuseoneormoreaccumulators-deviceswhichcontainpressurizedgaswhichcanaccommodaterapidpressurechangesinthefluidportionofthesystem.

Gravity,springsandcompressedgasesprovidepotentialenergyImanyhydraulicsystems.Thus,gravityassistisoftenusedtoreturnaparttoitsoriginalpositionwithouttheuseofpowerfromthehydraulicsystem.Thistypeofassistancealsosimplifiesthepartsinthehydraulicsystem.

PumpsMechanicalsealMeasures.Atpresentthemechanicalsealinpumpsinakindofproducttheapplicationextremelywidespread,butandwillsavetheenergyalongwiththeproducttechnicallevelenhancementtherequest,themechanicalsealapplicationprospectismorewidespread.Themechanicalsealsealeffectdirectlywillaffecttheentiremachinemovement,inparticularinpetroleumchemicalindustrydomain,becausewillexistflammable,explosive,iseasytovolatilize,tobeviolentlypoisonousandsoonthemedium.

 Themechanicalsealappearswilldivulge,seriouslywillaffecttheproductionnormallytocarryon,isseriousalsoappearsthesignificantsecurityaccident.Peoplewhenanalysisqualitybreakdownreason,oftenisfamiliarwithinthemechanicalsealownaspectsearchesthereason,forexample:

Mechanicalsealshapingwhetherappropriate,choiceofmaterialwhethercorrect,thepackingsurfacecomparedtopresseswhethercorrectly,rubsthevice-choiceiswhetherreasonableandsoon.Butisshortverymuchinthemechanicalsealexternalconditionaspectsearchesthereason,forexample:

Pumpsforthemechanicalsealcreationconditionwhetherappropriate,theservosystemdispositioniswhetherappropriate,buttheseaspectsreasonsoftenarecountformuch.

Thisarticleauthorfrompumpedhasanalyzedthereasonablemeasurewiththemechanicalsealexternalconditionanglewhichtheinfluencesealeffectseveralkindoffactorsandshouldadopt.1Principleandrequestthatmachinerysealsoff:

ThemechanicalsealisdependsonapairofrelativemotionlinkendsurfaceA（fixed,anotherrevolvestogetherwithaxis）themutualfittingformsthesmallaxialplayplaysthesealrole,thiskindofequipmentiscalledthemechanicalseal.Themechanicalsealusuallybymovesthelink,thestaticlink,contractsthepartandthesealpartiscomposed.Movesthelinkandthestaticlinkendsurfacecomposesapairtorub,movesthelinktodependoninthesealedchambertheliquidpressuretocauseitsshoulderuponthestaticlinkendsurface,andproducesontwolinksendsurfacessuitablecomparedtopressesandmaintainsanextremelythinliquidmembranetoachievethesealthegoal.Contractsthepartpressurize,maycausetopumpundertheoperatingcondition,alsomaintainstheendsurfacefitting,guaranteedthesealmediumnothingmorethanleaks,andpreventedtheimpurityenterssealstheendsurface.SealstheparttoplaythesealtomovethelinkandaxisgapB,thestaticlinkandtheglandgapCrole,simultaneouslytothevibrationwhichpumps,attacksthecushioningeffect.Themechanicalsealintheactualmovementisnotanisolatedpart,itiswithothersparepartswhichpumpscombinesthemovementtogether,simultaneouslymayseethroughitsbasicprinciple,themechanicalsealnormaloperationhasthecondition,forinstance:

Otherwisefleeingmeasuresapumpspindle'sbeingnotabletoverybig,frictionsubsidiaryendfacecannotformtheratiopressuredemandingregularly;Thepumpspindlethatmachineryhermeticsealinggetsalongcannothaveboundaryverybigdeflection,endfacewaitsaminuteotherwisethanpressurewillbeuneven.Besidesonlywhensatisfyingsimilarsuchexternalcondition,finemachinerysealsoffoneselffunction,abilityreachesidealhermeticsealingeffect.2Analysisofcausesthatexternalconditionaffects:

Pumpspindleaxialtofleeingismeasuredbig:

Thehermeticsealingthatmachinerysealsoffneedstohavecertainratiopressurefacetoface,suchabilityplaysarriveathermeticsealingrole,berequiringthatspringthatmachinerysealsoffneedstohavecertaincompressionamountsrightnow,giveapropulsiveforcesealingoffendface,rotatingmakeshermeticsealingproducethepressuresealingoffthewhatbedemandedratiofacetoface.Forensuringthatthisoneiscomparedtopressure,theamountsmachineryissealedoffrequiringthatthepumpspindlecan