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1、Unit1IntroductiontoBasicDevicesandsystemsManydifferentmachinesandprocessesuseafluidfordevelopingaforcetomoveorholdanobjectorforcontrollinganaction.Inautomobiles,forexample,hydraulicbrakesareusedtostopthecar.Inroadconstructionandrepair,anotherexample,compresse
2、dairisusedtooperatechippinghammers.Machinesandprocessedarebecomingmoreandmoreautomatedinordertomeetcompetitionandmoreautomatedinordertomeetcompetitionandtoreducehumanerror.HYDRAULICANDPNEUMATICSYSTEMSGenerallyspeaking,anumberoffluidscanbeusedindevicesandsyste
3、ms.Thetermhydraulicreferstoaliquid.Forexample,thetermhydraulicturbinecanbeusedtodesignateaturbineinvolvingwaterflow.Inahydraulicsystem,oil,water,orotherliquidcanbeused・Besidesaliquid,eitheragasoracompressiblefluidcanbeused・Inactualpractice,twofluidsarcmostcom
4、monlyisusedinthisbook,oiliscalleda"hydraulic“system.Afluidsystemthatusescompressedairiscalleda"pneumatic“system・Bothtypesoffluidsystemsaretreatedinthisbook.HydraulicSystemsFigJillustratesatypicalhydraulicsystem•Oilfromatankorreservoirflowsthroughatubeorpipein
5、toapump.Thepumpcanbedrivenbyanelectricmotor,airmotor,gasturbine,orinternalcombustionengine、Thepumpincreasesthepressureoftheoil;theoilpressureatthepumpoutletmaybe5to5000ormorepoundspersquareinch・High-pressureoilflowsinatubeorpipingthroughacontrolvalve;thisvalv
6、ecanbeusedtochangetheoilflow・Areliefvalveisusedtoprotectthesystem;thevalvecanbesetatadesiredsagemaximumpressure.Iftheoilpressureinthesystembeginstoriseabovethemaximumsafepressure,thereliefvalveopenstorelievethepressureandtopreventdamagetoeitherthesystemorthes
7、urroundings.Theoilthatentersthecylinderactsonthepiston;thispressureactionovertheareaofthepistondevelopsaforceonthepistonrod・Theforceofthepistonrodcanbeusedtomovealoadordevice・Oilfromthecylinderreturnstothereservoir.Astheoilpassesthroughthefilter,dirtandforeig
8、nmatterareremovedfromtheoil・Eachseparateunit、suchasthepump,thevalve,thecylinder,orthefilteriscalleda“component^ofthesystem・INTRODUCTIONTOBASICDEVICESANDSYSTEMSPISTONROOPUSH10MOVEfig.1Atyp
