液壓與氣壓傳動(dòng)（英漢雙語(yǔ)）第2版 教學(xué)課件作者 陳淑梅 第6章 Chapter-6

Chapter6AuxiliaryComponentsforHydraulicSystems

6.1Accumulators

6.2Filters

6.3Reservoirs

6.4Piping/TubingConnectors

6.5SealsandSealingDevices

Chapterlist6.1Accumulators6.1.1Operatingprinciples6.1.2Applications6.1.3Calculationofparameters6.1.1Operatingprinciples

Therearethreetypesofaccumulators:springloaded,weightloadedandchargedgas.Thecommonusedarechargedgasaccumlators,whichcanbedividedintopistontype(Fig.6-1a)andbagtype(Fig.6-1b).

Fig.6-2showsanaccumulator,whichbasicallyconsistsof4parts:shellbody1,interlayer3,compressibleair2(weightloadedorspring)ontheupperoftheinterlayerandoperatingoil4locatedundertheinterlayerandconnectedwithsystem.Itincludestwoprocesses:filledinoilfluid(accumulation)anddisplacementoutoilfluid(release).Fig.6-1Chargedgasaccumulator

a)Pistontypeb)Bagtype

1-Piston2-Cylinder3-Gasvalve1-Gasvalve2-Steelshell3-Bladder4-PoppetvalveFig.6-2Operatingprincipleofaccumulatora)Afterdisplacementoutoilfluidb)Filledinoilfluidc)Displacementoutoilfluid

1-Shell2-Compressiblegas(orweightorspring)3-Interlayer4-Operatingfluid

1.Filledinoilfluid(accumulation)ItisanequilibriumstateofpressuredifferenceonthetwosidesofupperanddownontheinterlayerwiththeoperatingoilvolumeasV1afterdisplacementoutoilfluid(release)showninFig.6-2a.Whenoperatingoilpressureintheaccumulatorisincreasedwiththeoilpressureinhydraulicsystem,theinterlayerlossesequilibriumandmovesupundertheactionofoperatingdifference,asshowninFig.6-2b.Itincludestwoprocesses:filledinoilfluid(accumulation)anddischargingoutoilfluid(release).2.Dischargingoutoilfluid(release)Whenthesystempressureislowerthanthepressureoftheoperatingoil,theinterlayismoveddownundertheactionofgaspressure(orweightloadedorspringloaded);atthesametimeoilisdischargedoutoftheaccumulatorandflowsintothesystemuntilanewpressureequilibriumonthetwosidesoftheinterlayerasshowninFig.6-2c.6.1.2Applications

Suchanaccumulatorcanbeusedtoadvantageinanumberofhydraulicapplications:1.Tosupplyoillostthroughleakageinasystemheldunderpressurebutnotoperatingforlongperiods.Toserveasanauxiliaryoremergencysourceofhydraulicpowerwherepumporfeedlinehavefailed.Tooperateasecondarycircuitintermittentlyinconnectionwithaconstantdutyprimarycircuitwithoutaffectingthespeedorloadingoftheprimarycircuit.Tocompensateforexpandingandcontractingvolumesduetothermalchanges.2.Tosupplyholdingpressurewheretheoperatingcyclecallsforpressuretobeappliedforalongperiodsoftime.Forexample,anaccumulatorcanbeusedtoavoidaccidentwhenthepumpfailsrandomicityatstarting.3.Toabsorbpulsations,surges,orshocksfromreciprocatingpumpsorquickclosingvalves.Tocushionandlowerthenoisetheloadonforklifts,frontendloaders,backhoes,etc.6.1.3Calculationofparameters1.CalculationforthechargedgasvolumeV0

Thevolumeofanaccumulatoristhechargedgasvolumeforabagaccumulator＝Constant（6-1）(1)Forthe

isothermalchanges

Theinvolvementnochangeintemperature,andnointernalenergychangesoccurinthe

gas.Taken=1,then（6-2）(2)Fortheadiabatic(isentropic)changes

Theotherboundingconditionisareversibleadiabatic(isentropic)changewhichtakesplacesorapidlythatnoflowofheatintooroutofthegasoccurs.Thedefiningrelationshipis(3)

Forpolytropicchanges

Practicallyaccumulatorgascanfollowanynumberofpolytropicchanged,whichisisothermalduringaccumulatingandadiabaticduringdischargingduetogasexpanded.Itcanbesocalculatedby（6-3）2.Determinationofpressure（1）

Calculationforlowestoperatingpressure

Thelowestoperatingpressureincludetwoparts,whichcanbecalculatedby（2）

Determinationofhighestpressure（6-5）（6-4）

Determinationofhighestpressureinanaccumulatorshouldconsiderthefactorsoflifetimeofsystemandstability.Belowanempiricalformulaisrecommended.（3）Determinationofchargedgaspressure

Forabagtypeaccumulator,

（6-7）（6-6）where:6.2

Filters6.2.1Functionsofafilter

6.2.2Thetypesoffilters6.2.1Functionsofafilter

Accordingtostatisticsthattherearefaultsof70%～80%duetotheoilcontaminated.Theoilcontaminatedwithimpurityoroxidewillresultinabrasionorblockofelementsquickenup.Thefilterisusedtotrytoeliminatetheimpurityandmakeacleanlyoilpipesystem.Thusitisimportanttochoosefilterforcontrollingthecontaminationandkeepinganormalhydraulicsystem.

Thetypesoffilters

Filtersaredividedintotwokindsofcoarseandprecisefiltersintermsoftheprecision.Theycanbedividedintomesh,

line-gap,paper-coreandmagnetismfiltersintermsofconfiguration.Andtheycanbealsodividedintothreeclassifies:surface-type,depth-typeandmagnetismfiltersintermsoftheprincipleoffiltration.1.Surface-typefilters

Fig.6-3a)Ameshfilterb)ALine-gasfilterThesurfaceofelementstouchesdirectlywithhydraulicmediumandconsistsofasinglelayerofmaterialthroughwhichthefluidmustpassandkeeptheimpurityoutsideonit.epth-typefilters

Thecorematerialconsistsofpaper,sinteredmetal,woolfeltorvariousfibres～～0.2MPaandusuallyusedinahighprecisionsituation.Fig.6-4a)Apaper-corefilterb)Asinteredfilter

Theprincipleofmagnetismfiltersisanabsorbent-typeelement,whichabsorbstheferrousparticleintheoil.Howeveritcannotabsorbtheothernonferrousparticle.Soitisusuallycombinedwithothertypeoffiltersandusedinhydraulicsystemformetal-cuttingmachinetool.3.Magnetismfilters

Reservoir1.Constructionandfunctions

Functions:

Areservoirprovidesoiltomakeupforsystemleakage,allowsspacefortheexpansionorcontractionoftheoilwithchangesoftemperature,enablesgasbubblestoriseoutoftheoilanddirtparticlestosinktothebottom,andallowsroomforheatdissipationorfortheinclusionofthermalcontroldevices.

Therearetwokindsofreservoirs:integraltypeandseparateness.

Aintegralreservoirisinstalledwithmachine;ithastheadvantagesofcompactandeasyrecyclesforleakedoilbutalsothedisadvantagesofdifficultdissipationforheatanddifficultmaintenance.Theseparatenessreservoirisseparatelyinstalled;ithasbeenusedwidelytoengineeringwithmanyadvantagesofconvenientmaintenance,dissipationheatandreducingvibration.Fig.6-5showsasmallseparatereservoir.Fig.6-5Asmallseparatereservoir1-Meshfilter2-Suctionoilpipe3-Airfilter4-Oilchargedpipe5-Topcover6-Indicatorofoilposition7，9-Clapboard8-OilescapevalveProblemsindesign

1）Thedeterminationtothecapacityofreservoiristhekeytothewholereservoirdesign.

2)Areservoirisusuallyjointedbyarmorplatewithathicknessof2.5~4mm.Angleironisalsoneededforreservoirswithlargecapacitytoincreasetheirrigidity.

3)Suctionfiltersaresettoassureenoughflowrate.Itmustbeconvenientforassemblyanddisassembleforthesakeofregularcleanness.

4)Suctionlinesarekeptawayfromreturnlinesasfaraspossible.Usuallyaclapboardwithaheightofthe3/4oillevelissetbetweenthemtoincreasethedistanceoftheoilcycleandhelpheat-exchange,sedimentation,airbubbleseparation.Theendsofthesuctionandreturnlinesarechoppedin45°.Thedistancebetweenthefilterandthereservoirbottommustbelongerthan20mm.5)Thecoverboardofthereservoirandtheendsofthepipesmustbesafelysealedtopreventoilcontamination.Anairfilterissetonthecoverboard.Italsoservesasaventholetopreventnegativepressureonthereservoirorintheprocessofaddingoil.6)Anoillevelgaugeandathermometerareusuallysetonthesidewallofthereservoir.

Thedetailedinformationcanbefoundinrelatedbooksormanuals.6.4Piping/TubingConnectors

Pipingconnectorsincludeoilpipesandconnectors.Thefunctionsofpipingconnectionsareusedtojoinhydraulicelementsandtransferfluidconnectors.Pipingconnectionsshouldhavegoodstrength,sealing,lessleak,lowpressurelossandconvenientreplacementandfixing.1.Oilpiping

Pipingismadefromavarietyofmaterials,includingsteel,copper,nylon,plastics,andrubberpipe.Itisdecidedbysystempressureandoperatingconditions.ThefeaturesandapplicationarelistedinTab.6-1.Tab.6-1ThefeaturesandapplicationsofvariousoilpipesTypesFeaturesandapplicationsTubingesAsteeltubeIthasthefeaturesofwithstandingoilandhighpressure,highstrengthandworkingstably.Butitisdifficulttobebendedininstallation.Itisusuallyusedasapressurewhereoneiseasytoinstallation.Theseamlesssteeltubeisusedinabovemediumpressuresystem.JointedtubingisusedinalowpressuresystemAcopperpipeItisexpensiveandhaslow-pressurepipelincapacity(6.5～10MPa).Itwithstandswithalowshockandvibration.Itiseasytobebendedandcorrosive.Itiscommonusedtowherethesystemisdifficulttoinstallation,suchasinstrumentHosesAplasticpipeIthasthefeaturesofwithstandoil,lowprice,convenientinstallation,andeasytoagingforalongused.Itisusedinlowpressure(<0.5MPa),suchasreturnoilpipesAnylonpipeItisaivory-whiteandsightflowing.Ithaslowpricewhenitheateditiseasytobebended.Itiseasytobebended,enlargedandformedaftercooling.Itiseasytoinstallation.IthasthepossibleofexpandingrangeofapplicationArubberpipeItisusedwherethehydrauliclineistobesubjectedtomovement.Ithastwotypesoflowandhighpressurehose.Thehighpressurehoseismadewithseveralpliesofbraidedsteelwirereinforcementtowithstandworkingpressures.Itisexpensiveandusedinahighpressuresystem.Thelowpressurepipeismadeofresistantoilrubberwithpliesofsailcloth,whichisusedinlowpressuresystemJustasothertubularmaterials,tubingismeasuredbyitsinsidediameterd,andthicknessδofawall.（6-19）（6-20）2.Connectors

Connectorsmorefrequentlycalledfittingsareusedtojoinpipelinesandtoconnectpipelinestocomponents.Nomatterwhattheconfigurationoftheconnectorisused,itperformsthreetasksunderenoughintensity:(1)theconnectormustjointothelineinafirm,leakproofmanner.(2)theconnectormustnotcarryanyloadsimposedonitbythehydraulicsystemorbytheline.(3)theconnectormustprovideasealbetweenthepartsbeingjoined.Tubingconnectordesignbynationalstandards,metricinternationalstandardthread,isdenotedasZMorplainEnglish(standard)threaddenotedasM.Theyincludeflaredshapeconnectors(Fig.6-6),joiningstyleconnectors(Fig.6-7),clipstyleconnectors(Fig.6-8),hosepipeconnectors(Fig.6-9)andquickconnectors.Fig.6-6Aflaredshapeconnector

1-Pipeconnected2-Orientedsleeve3-Nut4-ConnectionbodyFig.6-7Ajoiningstyleconnector

1-Pipeconnected2-Nut

3-“O”ringseal4-Connectionbody5-

CompoundSealsFig.6-8Aclipstyleconnector

1-Pipeconnected2-Clip3-Nut4-Connectionbody5-CompoundSealsFig.6-9Ahosepipeconnector

1-Rubberpipe2-Shell3-Connectionbody4-NutFig.6-10Aquickconnector1-Pad2，10-Connectionbody3，7，12-Spring4，11-Coreofno-returnvalve5-“O”ringseal6-Shell8-Steelball9-Springring6.5SealsandSealingDevicesThesealingdevicesareusedtopreventoilfrominternalandexternalleakage,holdbackpollutantandkeepthesystempressure.Typesandcharacters:

Therearemanykindsofsealingdevices.Accordingtothemovementofthesealingdevices,therearetwomainkindsofsealingdevices:dynamicandstatic.1.Clearancesealing2.‘o’ringsealingAsshowninfig.6-11.Asshowninfig.6-12.Fig.6-12‘o’ringsealingFig.6-11Clearancesealing

Fig.6-13‘o’ringwith