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1、黑龙江工程学院本科生毕业设计附录附录A英文部分：Thecommonlyusedsourcesofpowerinhydraulicsystemsarepumpsandaccumulators.Similarly,accumulatorconnectedtoatmospherewilldischangeoilatatmospherepressureuntilitempty.onlywhenconnectedtoasystemhavingresistancetoflowcanpressurebedeveloped.Thr
2、eetypesofpumpsfinduseinfluid-powersystems:1,rotary,2,reciprocating,3,orpiston-type,and3,centrifugalpumps.Simplehydraulicsystemmayusebutonetypeofpump.Thetrendistousepumpswiththemostsatisfactorycharacteristicsforthespecifictasksinvolved.Inmatchingthecharacterist
3、icsofthepumptotherequirementsofthehydraulicsystem,itisnotunusualtofindtwotypesofpumpsinseries.Forexample,acentrifugalpumpmaybetosuperchargeareciprocatingpump,orarotarypumpmaybeusedtosupplypressurizedoilforthecontronlsassociatedwithareversingvariabledisplacemen
4、tpumps.Mostpowersystemsrequirepositivedisplacementpumps.Athighpressure,reciprocatingpumpsareoftenpreferredtorotarypumps.RotarypumpsThesearebuiltinmanydifferntdesignsandextremelypopularinmodernfluidpowersystem.Themostcommonrotay-pumpdesignsusedtodayarespurgear,
5、internalgear,generatedrotor,slidingvane,andscreewpumps.Ehchtypehasadvantagesthatmakeitmostsuitableforagivenapplication.GearpumpsGearpumpsarethesimplesttypeoffixeddisplacementhydraulicpumpavailable.Thistypeconsistsoftwoexternalgear,generallyspurgear,withinaclos
6、ed-fittinghousing.Oneofthegearisdrivendirectlybythepumpdriveshaft.It,inturn,thendrivesthesecondgear.Somedesignsutilizehelicalgears,butthespurgeardesignpredominates.Gearpumpsoperateonaverysimpleprinciple,illustrationFig.7.3.Asthegearteethunmesh,thevolumeatthein
7、letportAexpands,apartialvacuumonthesuctionsideofthepumpwillbeformed.Fluidfromanexternalreservoirortankisforcedbyatmosphericpressureintothepumpinlet.ThecontinuousactionofthefluidbeingcarriedfromtheinlettothedischargesideBofthepumpforcesthefluidintothesystem.11黑
8、龙江工程学院本科生毕业设计Pressureriseinaspur-gearpumpisproducedbythesqueezingactiononthefluidasitisexpelldefrombetweenthemeshinggearteethandthecasing.Fluidfromthedischargesideispreventedfromre
