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1、PNEUMATICS GeneralPneumatics,fromtheGreekｹνευματικός(means-comingfromthewind)Pneumaticswasfirstdocumentedin60A.DPascal'sprinciple,statesthatpressureisconstantthroughoutastaticfluid.Pneumaticsaregenerallyusedforapplicationsinvolvinglessforcethanhydraulicapplications.Pneumat
2、icsmaybecontrastedwithhydraulics,whichusesincompressibleliquidmediasuchasoilorwaterinsteadofair.Airiscompressible,isconsideredtobeafluid,andmostindustrialapplicationsuseapproximately80to100poundspersquareinch(psi)gaugepressure,ascomparedtohydraulicswhicharecommonlyusedfrom
3、1,000to5,000psi,andinsomecases10,000psiandhigher.Bothpneumaticsandhydraulicsareapplicationsoffluidpower.Physicalpneumaticprinciplesconcludethatthepressurethatformsincompressibleliquidscanbeharnessedtoahighpotentialofpower.Pneumaticsystemscanprovidescompressedairataconstant
4、flowratetoairconditioningunits,whereitstemperatureiscontrolledanditisductedintothecabin.Pressurizationsystems,restrictstheescapeofairfromthecabintomaintainproperpressurizationinthecabin.Thepneumaticsystemalsoprovidescompressedairforenginestarting.Theenginecompressors,auxil
5、iarypowerunit,oragroundunitcanbeusedtosupplythepneumaticsystem.Thepneumaticmanifoldisnormallysuppliedfromtheengines.TheAPUoranexternalairsourcemayalsobeused.InstructionalpurposesonlyPNEUMATICS-APPLICATIONSAPPLICATIONSSomeexamplesPressurizationAnti-iceDe-iceRainremovalLifte
6、nhancementAirconditioningEnginestartingPneumaticbrakingOtherPressurizationPressurizedairforthecabincomesfromthecompressorstagesintheaircraft'sjetengines.Movingthroughthecompressor,theoutsideairgetsveryhotasitbecomespressurized.Theportiondrawnoffforthepassengercabinisfirstc
7、ooledbyheatexchangersintheenginestrutsandthen,afterflowingthroughductinginthewing,isfurthercooledbythemainairconditioningunitsunderthefloorofthecabin.Thecooledairthenflowstoachamberwhereitismixedwithanapproximatelyequalamountofhighlyfilteredairfromthepassengercabin.Thecomb
8、inedoutsideandfilteredairisductedtothecabinanddistributedthroughoverheadoutlets.Comparedt
