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.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
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