Pneumatic and Hydraulic Systems

11PneumaticSystems9Pneumaticsystemsaredesignedtomoveloadsbycontrollingpressurizedairindistributionlinesandpistonswithmechanicalorelectronicvalves.9Airunderpressurepossessesenergywhichcanbereleasedtodousefulwork.9Examplesofpneumaticsystems:dentist’sdrill,pneumaticroaddrill,automatedproductionsystems.Chapter7PneumaticandHydraulicSystems229Compressoristhepowersourceofapneumaticsystem.Itisusuallydrivenbyamotororaninternalcombustionengine.Thecompressedairisfirststoredinastrongmetaltankcalledreservoir.9Beforeenteringthecylindersandvalves,thecompressedairhastopassthroughtheairtreatmentdevices,includingairfiltertoremovedustandmoisture,pressureregulatortoadjustpressure,andlubricatortospraylubricationoil.motorcompressorreservoirdistributionlinesairtreatmentcylindersandvalvesComponentsofaPneumaticSystem33airfiltercondensedwaterwaterreleasevalveAirFilter--toremovedustandmoisture44PressureRegulator--toadjustpressureadjustscrewspringvalvediaphragmventilationhole55Lubricator--tospraylubricationoillubricationoilsiphontube66PneumaticActuator--Cylinder9Cylinderistheactuatorinthepneumaticsystem.Whencompressedairflowsintoacylinder,energystoredintheairwillrelease,transferringintokineticenergytodowork.compressedairexhaust77Example1.Calculatingtheforceproducedbyacylinder9Theinputairpressureis0.5MPa,whichmeanstheairwouldexertaforceof0.5Noneachsquaremillimeters.Iftheareaofthepistonis300mm2,thenthetotalforceproducedbythecylinderwillbe:force=pressure×pistonarea=0.5N/mm2×300mm2=150N壓縮氣體0.5MPa2mm300compressedair0.5MPa88PneumaticMotor–PistonTypeandVaneTypeinletoutletpistonpistonrodoutputshaft99bladespringanvilairoutletpistonairinletcontrolleverairflowdiskvalveairflowairduct(a)(b)Example2.PneumaticDrill1010PressureControlValve–RelieveValveadjustscrewspringballvalve9Reliefvalve,alsoknownassafetyvalve,isusedtomaintainthedesiredpressure.1111PressureControlValve—ReduceValveadjustscrewspringdiaphragm減壓閥表示符號1212DirectionalControlValve–TwoPortValve(2/2)OUTINOUTIN9Directionalcontrolvalvesarecommonlydescribedbyanx/ydesignation,wherexisthenumberofportsandyisthenumberofpositions.92/2valve:2ports,2positions.9Thetwoportvalveissimilartothesinglepolesinglethrowswitchinelectriccircuits.1313231DirectionalControlValve–ThreePortValve(3/2)9Thethreeportvalveissimilartothesinglepoledoublethrowswitchinelectriccircuits.123彈簧出氣口氣壓源123彈簧出氣口氣壓源exhaustairsupplyspring1414Example3.PneumaticPunchingMachine(I)氣壓缸方向控制閥沖壓模singleactingcylinderthreeportvalve(3/2)punchingmold1515Example3.PneumaticPunchingMachine(II)1321322(a)(b)1321322(a)(b)16169Theonewayvalveallowsairflowfromonlyonedirection.Itissimilartothediodeinelectriccircuits.球閥止回閥表示符號ballvalveDirectionalControlValve–OneWayValve17171B1A22111B1A2閥梭動閥氣壓表示符號valve9Ashuttlevalvehasthreeportsandcontainsasmallrubberpistonwhichisfreetomovebetweenport1Aand1Bwithinthevalve.9Ifairentersthevalvethroughport1Aor1B,thepistonispushedtotheothersideandaircanonlyescapethroughport2.DirectionalControlValve–ShuttleValve1818Example4:DualControlPneumaticPunchingMachine123123ABabCD1919FlowControlValve–theFlowRegulator9Aircanpassthroughtheregulatorineitherdirection.9Ifairentersfromleft,theballvalveispushedopenandaircanflowthroughthevalveunrestricted.9Ifairentersfromright,theballvalveisclosedsothataircanonlypassthroughtheregulator.9Theflowofaircanbecontrolledbyturningafingerscrew.球閥彈簧調整螺栓INOUT針形閥fingerscrewneedlevalvespringballvalve2020ControlofDoubleActingCylinders(I)流量控制閥五口二位置方向閥fiveportvalve(5/2)flowcontrolvalve2121ControlofDoubleActingCylinders(II)9Unlikeasingleactingcylinder,adoubleactingcylinderdoesnotcontainareturnspring.Movementsinbothdirectionsarepoweredbycompressedair.9Theflowcontrolvalvemakesthedownwardmovementofpiston2slowerthanthatofpiston1.However,bothpistonsmoveupwardatthesamespeed.513513122222AirOperatedValves9Inthevalvesdescribedsofar,thespoolwhichcontrolstheflowofairismovedmechanically,byabuttonorlever.9Inordertobeautomated,directioncontrolvalvesinthepneumaticsystemshavetobecontrolledbyairpressureorelectricalsignals.9Inairoperatedvalves,thespoolismovedbyairpressure.351243122323Example5:ApplicationofAirOperatedValves123352314211412安全區域123352314211412安全區域saferegion2424PneumaticSolenoidValves9Thespoolpositionismovedbyanelectricalsolenoid,andcancontrolledelectronically.+V+V電磁線圈閥(b)(a)electricalsolenoidspool2525Hydraulics400N50NBA800mm2100mm2Pascal’sLaw9Theworkingfluidinahydraulicsystemisincompressible.Thusahydraulicsystemcanmovelargeloads.2626HydraulicSystemsoilreservoirmotoroilpumphydraulicvalvescylinder9Pneumaticsystemsareopensystems,alwaysprocessingnewair,andairissimplyexhaustedtotheatmosphere.Hydraulicsystemsareclosedsystems,alwaysrecirculatingthesameoil.2727Example6.HydraulicJackhandlesmallpistonone-wayvalvevalvereleasescrewlargepiston9Onlyasmallforceisrequiredbytheoperatortoraisetheheavyload.Thelargepistoncanbestoppedatanypointbecausetheoilcannotbecompressed.2828HydraulicActuators9Inahydraulicsystem,theactuatorstransferringhydraulicenergyintomechanicalmotionarehydrauliccylindersandhydraulicmotors.9Thereare3typesofhydraulicmo