液压与气压传动(英汉双语)第2版 教学课件 第2章 Chapter

Chapter2FundamentalHydraulic

FluidMechanicsChapter2FundamentalHydrau2.1

PerformancesoftheHydraulicOil

2.2Hydrostatics

2.3Hydrodynamics

2.4CharacteristicsofFluidFlowinPipeline2.5FlowRateandPressureFeaturesofOrifice

2.6 HydraulicShockandCavitation

Chapterlist2.1PerformancesoftheHyd2.1.1TheMainperformances2.1.2Therequestsandchoiceofhydraulicoil

2.1PerformancesoftheHydraulicOil

2.1PerformancesoftheHydra1.Density(kg/m3)

2.Compressibility

2.1.1TheMainperformances

thecoefficientofcompressibility,isthebulkmodulusofelasticity(2-2)(2-1)isdefinedastheratioofthechangeinpressure()torelativechangeinvolume()whilethetemperatureremainsconstant.

1.Density(kg/m3)3.Viscosity

TheexperimentshaveprovedthatfrictionforcebetweenthetwofluidmoleculescanbedescribedasWhereisviscositycoefficient,alsokinematicviscosity.Fig.2-1Thesketchofviscosity

ThesketchofviscosityisillustratedbyFig.2-1.

(2-3)Cohesionbetweentwomolecules……3.ViscosityTheexperimentshTherearethreemethodstodescribetheviscosity:absoluteviscosity,Kinematicviscosityandrelativeviscosity.(1)Dynamicviscosityorabsoluteviscosity

μ(Pa•s)or(N•s/m2)(2)Kinematicviscosityν(mm2/s)(2-4)(3)

Relativeviscosity(conditionalviscosity)Therelativeviscosity

whichusedinChinaistestedbytheviscometer,suchasFig.2-2.TherearethreemethodstodesFig.2-2Principleofviscometer

Fig.2-2PrincipleofvisTakethenotedescribestheviscosity:Theconversionformulabetweentheandkinematicviscosityis

(m2/s)

(4)Viscosity-temperature:Fortheviscositylessthan15andthetemperature30℃～150℃,theviscosity-temperatureformulaisdescribeasfollowing(WecanalsolookupfromFig.2-3):(2-5)(2-6)(2-7)(5)Viscosity-pressure(2-8)(6)Othersperformances

:physicalandchemical,suchasanti-inflammability,anti-oxygenation,anti-concreting,anti-foamandanti-corrosionetc.TakethenotedescribesthFig.2-3Theviscosity-temperatureofhomemadeoils

Fig.2-3Theviscosity-tempera2.Choice

Thehydraulicoilinahydraulicsystematisrecommendedgenerally.Request

Theoilplaystworolesoftransmissionenergyandlubricationonthesurfacesofworkinginteraction.

Therequestsforthehydraulicfluidsare:appropriateviscosity,thegoodinpropertyoffavorableviscosity－temperature,agoodlubricity,chemicallyandenvironmentallystabilities,compatiblewithothersystemmaterialsandsoon.2.1.2Therequestsandchoiceofhydraulicoil

Thehydraulicoilshouldbechoseninaccordingtotherequestofhydraulicpump.ThehydraulicoilviscosityadaptedfordifferenthydraulicpumpsislistedinTab.2-2.2.ChoiceRequest2.1.2ThereTab.2-2TherangeofviscosityofhydraulicoiladaptedtopumpsTypesviscosities(10-6m2/s)TypesViscosities(10-6m2/s)5～40℃①40～80℃①5～40℃①40～80℃①VanePumpsP<7MPa30～5040～75Gearpumps30～7095～165P≥7MPa50～7050～90Radialpistonpumps30～5065～240Screwpumps30～5040～80Axialpistonpumps30～7070～150①5～40℃、40～80℃aredescribedthetemperaturesofhydraulicsystem.Tab.2-2Therangeofviscosit2.2.1CharacteristicsofHydrostatics2.2.2

Thebasicformulaofhydrostatics2.2.3TheprincipleofPascalapplication2.2.4Effectoffluidpressureoncurvedsurfaces2.2

Hydrostatics

2.2.1CharacteristicsofHy1.ThehydrostaticsStaticpressure:theactionforceinnormalonaunitarea.Itisintituledpressureinphysicsandactionforceinengineeringusually.

2.Thecharacteristicsofhydrostatics

(1)Inanyhomogeneousfluidsystematrest,thepressureincreaseswiththedepthofthefluid.(2)Pressureatanypointinahomogeneousfluidsystematrestactsperpendicularlytosurfacesincontactwiththefluid.2.2.1CharacteristicsofHydrostatics

1.Thehydrostatics.2Thebasicformulaofhydrostatics

Thebasicformulaofhydrostatics

Theactingpressuresonthefluidatrest,inacontainerincludetheweight,forceonthefluidsurface,showninFig.2-4a.

Fig.2-4ThedistributionofforcesinacontainerwithrestfluidThetotalbalanceforceformulais

Formula(2-9)divideby,then

(2-9)(2-10)2.2.2ThebasicformulaofhyThepressureonarestfluidcontainedinvolvestwoparts:

Theformula(2-10)isthebasicequationforhydrostatic.Itstatesthatthedistributionstatusofhydrostaticsasfollowing:(2)Thepressureisincreasedwiththedepthh;(3)Isotonicpressuresurface,thatis,thepressuresareallequalatthesurfaceconsistedbyallpointsatgivendepthh,suchasatthelineofA-A;(4)Conservationofenergy

(2-11)(2-12)Here,theaspressureenergyatperunitmassfluid.Thepressureonarestfluidc2.Thedefinitionofpressure(1)AbsolutepressureRelativegaugepressure：Thepressuresmeasuredbyapressuregaugeareallrelativepressure(3)Vacuum(negativepressure)

1Pa＝1N/m2；1bar＝1×105Pa＝1×105N/m2;1at＝1kgf/cm2=9.8×104N/m2;1mH2O＝9.8×103N/m2;1mmHg＝1.33×102N/m2.

TherelationshipofthreepressuresisshowninFig.2-5.Theunitsofpressureandrelationsbetweendifferentpressures：2.Thedefinitionofpressure1Fig.2-5Absolute,relativeandvacuumpressureFig.2-5Absolute,relativeanExample2-1:Theoilisfullinacontainer.Foragivencondition,thedensityofoil,theactionforceonthispistonsurfaceF＝1000N,theareaofpistonＡ=1×10-3(m2),ifthemassofpistonisneglected,trytocalculatethestaticpressurepath=0.5ｍ,asshowninFig.2-6.Fig.2-6CalculationoffluidstaticpressureExample2-1:Theoilisfulli2.2.3

TheprincipleofPascal

TheprincipleofPascal:pressureexertedonaconfinedliquidistransmittedundiminishedinalldirectionsandactswithequalforceonallequalareas.ItsapplicationisshowninFig.2-7.Fig.2-7TheexampleofPascalprinciple2.2.3TheprincipleofPascal(1)Whenthewallisplane：F=PA(2)Whenwallisacurvedsurface：2.2.4Effectoffluidpressureoncurvedsurfaces

Example2-2.Fig.2-8showsacylindricalmemberofinsideradiiroflength.Calculation:theeffectforceFx

ontherightsegmentofthecylinderatxdirection.Fig.2-8Effectforceontheinnersurfaceofthecylinder

(1)Whenthewallisplane：F=2.3

Hydrodynamics

2.3.1Equationofcontinuity—conservationofmass2.3.2BernoulliEquation—conservationofenergy2.3.3Equationofmomentum—conservationofmomentum

2.3Hydrodynamics2.3.1EqTheequationsofcontinuity,Bernoulliandmomentumarebasicmotionequationsthatdescribethedynamicslawsinflowingfluid2.3.1

Theequationofcontinuity—conservationofmass

Fig.2-9sketchofconservationmassaccordingtotheconservationofmass,Forincompressibleflow,,OrconstantFormula(2-16)istheequationofflowcontinuity.

（2-14）(2-15)

（2-16）TheequationsofcontinTheassumptions:noenergyloss(meansin-viscidandincompressible),accordingtheequationofBernoulli—Conservationofenergy.OrFormulas(2-17)isthewell-knowBernoulliequation.Itstatesthatidealfluidincludepressureenergy,potentialenergy,andkineticenergy.Thesethreeenergiescanbetransferredbetweeneachother,butthetotalenergyisalwaysinvariable.

2.3.2BernoulliEquation—conservationofenergyFig.2-10SketchofBernoulliequation

(2-17)1.IdealequationofBernoulliTheassumptions:noenerg2.RealequationofBernoulliInmanyhydraulicsystems,theenergiescanbelost(thetotallossisdescribedashw),ontheotherhand,therealvelocityisanon-uniformdistributionandsetakineticcorrectionfactortooffsetthislost,andthecoefficientdefinedby:Hereα=1.1whenitisturbulentflow,andα=2whenlaminarflow,butusuallyinpracticesettheα=1.

Afterintroducingtheenergylossandkineticcorrectionfactor,theequation(2-17)willbechangeto(2-18)(2-19)Notes：seep27,(1)across-sectionarea1and2shouldbeselectedalongthestreamlinedirectionoffluidflow……2.RealequationofBernoulli3.ApplicationexampleoftheequationofBernoulli

Example2-3TheVenturimetershownreducesthepipediameterfrom0.1mtoaminimumof0.05masshowninFig.2-11.Calculatetheflowrateandthemassfluxassumingidealconditions.Fig.2-11Venturemeter

3.ApplicationexampleoftheExample2-4.TrytoanalysetheconditionofapumpdrawingintooilfromareservoirbytheequationofBernoulli(Fig.2-12).Setthepressureat2-2across-sectionisp2,thepressureat1-1across-sectionisp1,andp1=pa.andthedistancefrompumporificetohydraulicoilsurfaceish.Fig.2-12SetupofhydraulicpumpExample2-4.Trytoanalyseth2.3.3Equationofmomentum-conservationofmomentumFig.2-13SketchofoilflowthroughapipelinewithapressurevesselFig.2-14Sketchofoilflowthroughapipeline

Fig.2-15SketchofoilthroughcurvedpassagesInanysystemofabove,therateofchangeofmomentuminthesystemequalsthenetappliedexternalforce.

Theequationlooksthesameastherelationship(2-20)(2-21)2.3.3Equationofmomentum-con

Assumeafrictionless,incompressibleliquidinacylindricalpassageasshowninFig.2-14.

Theforcebalanceis,fromequation(2-20):

Because

q=Av,so

(2-22)(2-23)(2-24)AssumeafrictionlesFig.2-15,isachangeinmomentumasdefinedinequation2-20.TheforcescanberesolvedintoacomponentFxwhichisaxialtotheinletdirectionandacomponentFywhichisnormaltotheinletdirection.

(2-25)Fig.2-15,isachangeinExample2-5.Fig.2-16showsasketchofaspoolvalve.Whenoilfluidflowthroughthevalve,calculate:theaxialeffectforceofoilfluidonthespoolsurface.Fig.2-16Hydraulicdynamiconthespoolvalve

Example2-5.Fig.2-16showsaExample2-6.Fig.2-17showsasketchofapoppetvalve,wherethepoppetcoreis2.Whenfluidrateflowqthroughthevalveunderthepressureandthefluidflowdirectionat

bothstatusesofout-flowingFig.2-17

aandin-flowingFig.2-17

b,calculate:actionforcemagnitudeanddirectiononthispoppetcore.Fig.2-17Hydraulicdynamiconthepoppetvalve

Example2-6.Fig.2-17showsaFortwocasesabovethefluidactionpressuresonthepoppetareallequaltoF.TheactiondirectionsareshowninFig.2-17aandFig.2-17brespectively.

FortheFig.2-17athefluiddynamicpressuremakesthepoppetorificestendtobeclosed,andfortheFig.2-17btendtobeopened.Soweshouldbeconsideredaccordingtothedetailstatusandcouldnotconsideralltendspoolorificetobeclosedinanyconditions.Fortwocasesabovethe2.4.1StatesoffluidflowandReynoldsnumber

2.4.2Lossesalongcircleparallelpipe2.4.3Minorlossesinpipesystem2.4CharacteristicsofFluidFlowinPipeline

2.4.1StatesoffluidflowanWhenacontinuityviscousfluidflowsthroughvariablesection,fluidwilllosepartsofenergy.Thiscanbepresentedbythepressurelosshwandkineticcorrectionfactor

,i.e.,intheabovementionedrealfluidBernoulli’sequation

herehwincludestwoparts:pressurelossesalongparallelpipesandminor(orlocal)losses.

2.4.1StatesoffluidflowandReynoldsnumber

therearethreemainstatesofflow,suchaslaminar,transitionandturbulentinapipe.NowtakeFig.2-18forexample.WhenacontinuityviscFig.2-18.SetupofReynoldstestTheexperimentprovedthat,Reynoldsnumber,isconsistedofthreeparameters.TheReynoldsnumberwasobservedtobearatiooftheinertialforcetotheviscousforce.(2-26)1-Overflowpipe2-Supplypipe3,6-Reservoir4,8-Checkvale5-Smallpipe7-LargepipeFig.2-18.SetupofReynoldstisacriticalvaluebetweenlaminarandturbulenceusuallydeterminedbyexperimentaldata.(showinTab.2-3)pipesRecrpipesRecrsmoothmetalpipe2320Smoothpipewitheccentricannularitygap1000hosepipe1600-2000Columnvalveorifice260smoothpipewithconcentricannularitygap1100Poppetvalveorifice20-100Tab.2-3FamiliarcriticalReynoldsnumberbasedondifferentpipematerialForflowinnoncircularducts

(2-27)HereRishydraulicradius,definedby:(2-28)isacriticalvalueb2.4.2

Lossesalongcircleparallelpipe

Thelossesduetoviscosityinequaldiameterpipeisreferredaslossesinparallelpipe,whichwillchangewiththedifferentflowingstates.Lossesinparallelpipeatlaminarflow

(1)Velocityprofileinalaminarpipeflow

Fig.2-19Laminarflowinacirclepipe2.4.2Lossesalongcirclepa(2-29)

Integrateitandundertheboundaryofu=0atr=R,weobtain

Itsaysthatvelocityprofileinalaminarpipeflowalongradiidirectionisaparabolaprofileandthemaximumvelocityisattheaxiscenterr=0andAsshowinFig.2-19,aforcebalanceinthex-directionyields,thusSetthen

(2-30)(2-29)AsshowinFig.2-19,a(2)Theflowrateinpipe

Formula(2-32)saysthattheaveragevelocityis1/2ofthemaximumvelocity.（2-32）(2-31)Integrateitweobtain(3)Averagevelocityinpipe

Accordingtothedefinitionofaveragevelocity,Fromformula(2-30)(2)TheflowrateinpipeForm(4)LossesalongcircleparallelpipeFromformula(2-32),thelossis

Dosomechange,Theformula(2-33)canbewrittenas(2-33)(2-34)

Whereistheresistancecoefficientalongacirclepipe.Intheory,,butinapracticalcase,forametalpipe,forahosepipebecauseinfluenceoftemperatureneedtobeconsidered.(4)LossesalongcircleparallWhenturbulenceflowhashappened,Theexperimenthasshownthatresistancecoefficientis

Here∆isrelatedwithmaterialofpipe,suchassteeltube0.04mm,copperpipe0.0015～0.01mm，aluminum0.0015～0.06mmandhosepipe0.03mm.2.Lossesinparallelpipeatturbulenceflow

Theresistancecoefficientcanbecalculatedbyexperimentalformulaasfollowsforwater-powerslipperypipe,

（2-35）（2-36）

Thevelocityiswelldistributionatturbulenceflow,themaximumvelocityasWhenturbulenceflowhas2.4.3Minorlossesinpipesystem

Usuallytheminorlossescanbecalculatedby

Thereasonsofminorlosses:(2-37)

Thenwecancalculatetheflowrateexcepttheratingratebypressurelossformula,(2-38)2.4.3Minorlossesinpipesy

Thetotalenergylossesinawholehydraulicsystemcanbesummedaftercalculatingoutseveralsection’slossesby

(2-39)

Thetotalenergylossesi2.5.1Thinwallorifice

2.5.2Stubbyorificeorslotorifice

2.5.3Plateclearance

2.5.4Cylinderannularclearance

2.5

FlowRateandPressureFeaturesofOrifice

2.5.1Thinwallorifice

.1Thinwallorifice

ThinwallorificedefinedastheradioofflowlengthLtodiameteroforificedislessthan0.5asshowninFig.2-20,usuallytheorificeissharpedged.Fig.2-20Fluidflowthroughorifice2.5.1ThinwallorificeFig.

Fortheorificebeforeandaftersection1-1and2-2,TheBernoulliequationis

Thenwecanobtain

Hereisthespeedcoefficient.

(2-40)(2-41)Fortheorificebef

Thefluidflowratethatflowsthroughthisorificeasbelow,Where：A0—theacross-sectionareaofthisorifice；

Cc—thesectioncontractioncoefficient，；Cd—flowratecoefficient，Cd=CvCc。(2-42)ThefluidflowratethaInthecaseofcompletecontraction,,canbecalculated

InthecaseofRe＞105，=0.60～0.61inthecaseofincompletecontraction,canbeselectedbyTab.2-4Tab.2-4Flowratecoefficientsinincompletecontraction0.7Cd0.6020.6150.6340.6610.6960.7420.804

Thisisthereasonoflowresistancelosseswhenfluidflowsalongthelengthofthepipeinthinorifice.Ithaslesssensitivitytotemperature,andthinorificeisthususuallyusedtothrottleadjustor.Poppetandspoolvalveorificesaresimilartothethinorifice,sobothareallusedtothehydrauliccomponentorifices.(2-43)InthecaseofcompletecontraFig.2-21SketchofcylinderspoolorificeAisavalveseatBisaspoolcore

Theflowratethatflowthroughtheorificeiscalculatedbelowbyequationasfollow

Ifxv>>Cr，neglectCr,theflowrateas

TheflowratecoefficientcanbeobtainedbyFig.2-22,theReynoldsnumbercanbecalculatedbyfollowing,

(2-44)(2-45)(2-46)Fig.2-21SketchofcylinderAForahydraulicvalvewhateverflowinginorout,istheanglebetweenstreamlineandspoollineandiscalledspeeddirectionangle,itisusually.Fig.2-22Flowcoefficientontheorificeofspoolvalve

ForahydraulicvalvewhateThepoppetvalveorificeisshowninFig.2-23,Whenpoppetmovesupadistanceof,theaveragediameterof,,thentheflowrateis

Fig.2-23OrificeshapeofpoppetvalveFig.2-24Flowcoefficientofpoppetvalveorifice(2-47)WheretheflowratecoefficientcanbeobtainedbyFig.2-24Thepoppetvalveorificeissh2.5.2Stubbyorificeorslotorifice

Fig.2-25FlowratecoefficientsinStubbyorificeTheflowrateequationforslotorificeobeystheformula

(2-31),i.e.

Theflowrateequationforthestubbyorificeisthesameasformula(2-42),buttheflowratecoefficientcanbeobtainedfromthecurveinFig.2-25.Thestubbyorificeisdefinedas，slotorifice2.5.2Stubbyorificeorslot2.5.3

PlateclearanceFig.2-26FlowinparallelplainclearanceTheflowratefluidflowthroughtheplainplateclearanceis

（2-48）Theformula（2-48）hastwostatuses:1）Fluidflowatpressuredifferential:

（2-49）2）Fluidflowbyviscosityshear：（2-50）

ThefluidflowsunderpressuredifferentialandvelocityasshowninFig.2-PlateclearanceFig.2-2.5.4Cylinderannularclearance1.TheflowrateequationinaconcentricannularorificeFig.2-27showsasketchofconcentricclearanceflow

Fig.2-27SketchofconcentricclearanceflowLet’sconsiderannularclearanceexpandedalongthelengthdirectionisthesameasaplainplateclearance,sosubstitutingintoformula(2-48)

Ifthemotiondirectionofcylinderisthesameasthedirectionofpressuredifferential,thesymbolin(2-51)chooses“+”,otherwise“－”.theflowrateis(2-51)(2-52)2.5.4Cylinderannularcleara

asshowninFig.2-28,wecanabtainForverysmallclearances,isverysmalland,thenBecauseofsmallclearance，，

canbeconsideredasPlatesclearanceflow,theincrementalflowiswhereTheflowrateequationineccentricannularorifice

Fig.2-28Eccentricannularorifice(2-53)(2-54)(2-55)asshowninFig.2-28,wecanaIfe=h0，theflowisgreaterthanitwouldbeindicatedbytheuseofequation(2-51).Substitute（2-54）into（2-55）(2-56)(2-57)Integrating:Or

(2-58)Ife=h0，theflowisgreaterth3.TheflowratethroughaconicalannularclearanceBecauseofmachiningirregularities,suchaspistonorbore,valvecoreorseatcore,somedegreeofconicmustalwaysbeexpected,asshowninFig.2-29.Fig.2-29Fluidflowthroughaconicalannularclearancea)Converseconeb)Sequencecone

WhenitiscalledinversedegreeofconicasshowninFig.2-29a;

otherwisesequencedegreeofconicasshowninFig.2-29b3.TheflowratethroughaconForthestatusofFig.2-29a,substitutingintoformula(2-51),

Becauseh=h1+xtanθ,substitutingintoformula(2-59)：Integratingandsubstitutinginto

Weobtaintheflowrateas

(2-59)(2-60)(2-61)(2-62)ForthestatusofFig.2-29a,When，flowrateis

Integratingformula(2-61)thepressuredistributioninthisclearanceflowing,andsubstitutingtheboundaryconditionath=h1，p=p1,weobtainSubstitutingformula(2-62）andinto(2-64)，

,Whenu0=0,wehave

(2-64)(2-63)(2-65)(2-66)When，flowrate

ForthestatusofFig.2-29b,thesequencedegreeofconictheflowrateformulaisthesameastheformula(2-62),butpressuredistributionwhenis

or

(2-67)(2-68)ForthestatusofFig.2-4.HydrauliclockandforceIfthereisaeccentricity“e”betweenspoolcoreandseatduetosetting,asshowninFig.2-30.Eccentricwithinverseorderconicalannularb)Eccentricwithinorderconicalannularc)Sectionfigureatanypointd)SpoolcorenotchedbalancepressureFig.2-30Fluidflowthroughaconicalannularclearancewitheccentric4.HydrauliclockandforceThevalueof“h”atanypointis

(2-69)（1）Forthecaseofeccentricwithinverseorderconicalannularclearance(Fig.2-30a):thesideforceFwillenlargetheeccentricvalue“e”(Fig.2-30a)tomakethespoolcorelockedonthewallofseat.Since

，fromtheequation(2-66),thepressureatpointofislessthanthatat，i.e.(Fig.2-30c).

Thevalueof“h”atanypoint（2）Forthecaseofeccentricwithinverseorderconicalannularclearance(Fig.2-30b)：thesideForceFwillbecreatedanditwillreducetheeccentricvalue“e”(Fig.2-30b)tomakethespoolcorecenteredintheseat.Infact,thehydrauliclockisobjectiveandwhatwecandoistotrytoeliminateit.Themostsimplemethodisbalancenotchesonthespoolcore.

（2）Forthecaseofeccentricw2.6.1Hydraulicshock2.6.2Cavitation2.6

HydraulicShockandCavitation

2.6.1Hydraulicshock2.6Hyd2.6.1HydraulicShockHydraulicshockanddamagesThetypesofhydraulicshock

(1)Thatoccursduetothesuddenreductionoftheacross-sectionoftheorificeorchangeoftheflowdirection;(2)Thatresultsfromtheinertiaofthehighspeedworkingcomponentssuddenlybrakingorchangingdirection.2.6.1HydraulicShockHydrauli

1）Hydraulicshockresultsfromfluidflowstoppingsuddenly

Fig.2-31Hydraulicimpact

(2-70)

Thefluidflowisstoppedsuddenlywhenthecheckvalveisclosedsuddenly.Accordingtoconservationofenergy,So

1）HydraulicshockresultsfrSpreadspeedofshockwaveinpipecanbecalculatedby

(2-71)Formula(2-72)isinitituledthewholehydraulicshocksituation.Thepressurepeakvalueatnon-wholehydraulicshockislessthanthewholehydraulicshockanditcanbecalculatedby

(2-73)Formula(2-70)isonlyusedtotheclosedpipe,i.e.,thetimetofthecheckvalveclosedislessthanthetime(timeofcriticalclose).

(2-72)Spreadspeedofshockwavein2)Hydraulicshockresultesfromthemotionpartsbrakedaccordingtotheconservationofmomentum,thesystemshockpressurecanbecalculated:

Example2-7.Iftheinnerdiameterofpipeisd=200mm,thewallthickness10mm,theinitializationspeed,pressure,thebulkmodulusofelasticityoffluidMPa,themodulusofelasticityofpipematerialMPa.Calculatethemaximumpressuredropwhenthecheckvalveisclosedsuddenly.

2)Hydraulicshockresultesfr

Measurestoreducethehydraulicshock1)Prolongthetimeclosingcheckandmotioncomponents.2)Valveorificeofmotionworking-pieceisdesignedaccuratelymakingspeeduniformitychange.Expandproperlythediameterofpipe.Trytoshortenthelengthofpipe.Utilizerubbertubeoraccumulatoratpointofhydraulicshock.Measurestoreducethehydrau2.6.2Cavitatation

1.Theprincipleandharmofcavitation

Theprincipleofcavitation：Thephenomenonofcavitationhappenseasilyinsuctionofpumpandvalveorifice.

harm：air-corrosionwhichwilldamageworking-piecesofhydraulicmachineryandshortenthemachine’slife.2.6.2Cavitatation1.ThepriThemeasuretodecreasetheCavitation

1)Reducingthepressuredrop,usuallythespecialpressureiscontrolledp1／p2＜3.5.2)Whendesignitisbetterfortryingtoavoidnarrow,elboworsuddendirect