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HydraulicsystemandPeumaticSystemHui-xiongwan1,JunFan2Abstract:Hydraulicsystemiswidelyusedinindustry,suchasstamping,grindingofsteeltypeworkandgeneralprocessingindustries,agriculture,mining,spacetechnology,deepseaexploration,transportation,marinetechnology,offshoregasandoilexplorationindustries,inshort,Fewpeopleintheirdailylivesdonotgetcertainbenefitsfromthehydraulictechnology.Successfulandwidelyusedinthehydraulicsystem'ssecretliesinitsversatilityandeaseofmaneuverability.Hydraulicpowertransmissionmechanicalsystemsasbeingnotlikethemachinegeometryconstraints,Inaddition,thehydraulicsystemdoesnotliketheelectricalsystem,asconstrainedbythephysicalpropertiesofmaterials,itpassedalmostnoamountofpowerconstraints.Keywords:Hydraulicsystem,Pressuresystem,FluidThehistoryofhydraulicpowerisalongone,datingfromman’sprehistoriceffortstoharnesstheenergyintheworldaroundhim.Theonlysourcereadilyavailablewerethewaterandthewind—twofreeandmovingstreams.Thewatermill,thefirsthydraulicmotor,wasanearlyinvention.OneispicturedonamosaticattheGreatPalaceinByzantium,datingfromtheearlyfifthcentury.ThemillhadbeenbuiltbytheRomans.Butthefirstrecordofawatermillgoesbackevenfurther,toaround100BC,andtheoriginsmayindeedhavebeenmuchearlier.Thedomesticationofgrainbegansome5000yearsbeforeandsomeenterprisingfarmerisboundtohavebecometiredofpoundingorgrindingthegrainbyhand.Perhaps,infact,theinventorweresomefarmer’swives.Sincetheoftendrewtheheavyjobs.Fluidisasubstancewhichmayflow;thatis,itsconstituentparticlesmaycontinuouslychangetheirpositionsrelativetooneanother.Moreover,itoffersnolastingresistancetothedisplacement,howevergreat,ofonelayeroveranother.Thismeansthat,ifthefluidisatrest,noshearforce(thatisaforcetangentialtothesurfaceonwhichitacts)canexistinit.FluidmaybeclassifiedasNewtonianornon--Newtonian.InNewtonianfluidthereisalinearrelationbetweenthemagnitudeofappliedshearstressesandtheresultingrateofangulardeformation.Innon—Newtonianfluidthereisanonlinearrelationbetweenthemagnitudeofappliedshearstressandtherateofangulardeformation.Theflowoffluidsmaybeclassifiedinmanyways,suchassteadyornonsteady,rotationalorirrotational,compressibleorincompressible,andviscousornoviscous.AllhydraulicsystemsdependonPascal’slaw,suchassteadyorpipeexertsequalforceonallofthesurfacesofthecontainer.Inactualhydraulicsystems,Pascal’slawdefinesthebasisofresultswhichareobtainedfromthesystem.Thus,apumpmovestheliquidinthesystem.Theintakeofthepumpisconnectedtoaliquidsource,usuallycalledthetankorreservoir.Atmosphericpressure,pressingontheliquidinthereservoir,forcestheliquidintothepump.Whenthepumpoperates,itforcesliquidfromthetankintothedischargepipeatasuitablepressure.Theflowofthepressurizedliquiddischargedbythepumpiscontrolledbyvalves.Threecontrolfunctionsareusedinmosthydraulicsystems:(1)controloftheliquidpressure,（2）controloftheliquidflowrate,and(3)controlofthedirectionofflowoftheliquid.Hydraulicdrivesareusedinpreferencetomechanicalsystemswhen(1)powersistobetransmittedbetweenpointtoofarapartforchainsorbelts;(2)hightorqueatlowspeedinrequired;(3)averycompactunitisneeded;(4)asmoothtransmission,freeofvibration,isrequired;(5)easycontrolofspeedanddirectionisnecessary;and(6)outputspeedisvariedsteplessly.Fig.1givesadiagrammaticpresentationofthecomponentsofahydraulicinstallation.Electricallydrivenoilpressurepumpsestablishanoilflowforenergytransmission,whichisfedtohydraulicmotorsorhydrauliccylinders,convertingitintomechanicalenergy.Thecontroloftheoilflowisbymeansofvalves.Thepressurizedoilflowproduceslinearorrotarymechanicalmotion.Thekineticenergyoftheoilflowiscomparativelylow,andthereforethetermhydrostaticdriverissometimesused.Thereislittleconstructionaldifferencebetweenhydraulicmotorsandpumps.Anypumpmaybeusedasamotor.Thequantityofoilflowingatanygiventimemaybevariedbymeansofregulatingvalves(asshowninFig.7.1)ortheuseofvariable-deliverypumps.Theapplicationofhydraulicpowertotheoperationofmachinetoolsisbynomeansnew,thoughitsadoptiononsuchawidescaleasexistsatpresentiscomparativelyrecent.Itwasinfactindevelopmentofthemodernself-containedpumpunitthatstimulatedthegrowthofthisformofmachinetooloperation.Hydraulicmachinetooldriveoffersagreatmanyadvantages.Oneofthemisthatitcangiveinfinitely-variablespeedcontroloverwideranges.Inaddition,theycanchangethedirectionofdriveaseasilyastheycanvarythespeed.Asinmanyothertypesofmachine,manycomplexmechanicallinkagescanbesimplifiedorevenwhollyeliminatedbytheuseofhydraulics.Theflexibilityandresilienceofhydraulicpowerisanothergreatvirtueofthisformofdrive.Apartfromthesmoothnessofoperationthusobtained,agreatimprovementisusuallyfoundinthesurfacefinishontheworkandthetoolcanmakeheaviercutswithoutdetrimentandwilllastconsiderablylongerwithoutregrinding.HydraulicandpneumaticsystemThereareonlythreebasicmethodsoftransmittingpower:electrical,mechanical,andfluidpower.Mostapplicationsactuallyuseacombinationofthethreemethodstoobtainthemostefficientoverallsystem.Toproperlydeterminewhichprinciplemethodtouse,itisimportanttoknowthesalientfeaturesofeachtype.Forexample,fluidsystemscantransmitpowe