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1、Unit4HydraulicFluidsInhydraulics,hyraulicfluidsareusuallydividedintothreecategories—petroleum-basefluids,syntheticfluids,andwater.Thefirsttwofluidsareusedin“packaged-powerdevices.”Waterisgenerallyusedasthehydraulicfluidincentralhydraulicsystems.Thefunctionofago
2、odhydraulicfluidisthreefold:(1)itisameansoftransmissionoffluidpower;(2)itisameansoflubricationofthefluidpowersystem;and(3)itactsasasealant.Theselectionoftheproperhydraulicfluidisimportant,asithasadirectbearingontheefficiencyofthehydraulicsystem,onthecostofmaint
3、enance,andontheservicelifeofthesystem’scomponents.PETROLEUM-BASEFLUIDSThreebasictypesofmineraloilsareused:(1)Pennsylvania,orparaffin-baseoils;(2)GulfCoast,ornaphthenicandasphaltic-baseoils;and(3)Mid-Continent,ormixed-baseoils.Thesecontainbothnaphthenicandparaff
4、incompounds.Toobtaincertaincharacteristics,chemicalsareaddedtoanoil.Thesechemicalsarecalledadditives.Additivescannotmakeaninferioroilperformaswellasagoodoil,buttheycanmakeagoodoilperformevenbetter.Anadditivemaybeintheformofanantifoamagent,arustinhibitor,afilm-s
5、trengtheningagent,orandoxidationstabilizer.Theusershouldnotattempttoplaceadditivesinahydraulicoil.Thatjobisprimarilyfortheoilmanufacturerorrefiner.SYNTHETIC-BASEFLUIDSSinefirehazardsareprevalentaroundcertaintypesofhydraulicallyoperatedmachines,especiallywhereop
6、enfiresarepresent,muchresearchhasbeendonetodevelopfire-resistanthydraulicfluids.Thesefluidsaredividedintotwoclassificationssynthetic-basemixturesandwater-basefluids.Notallsynthetic-basefluidsareresistant.Synthetic-basefluidsincludechemicalcompounds,suchasthechl
7、orinatedbiphenyls,phosphateesters,ormixturescontainingeach.Thesehydraulicfluidsarefireresistant,becausealargepercentageofphosphorousandchloridematerialsareincluded.Water-basefluidsdependonahighpercentageofwaterofeffectthefire-resistantnatureofthefluid.Inadditio
8、ntowater,thesecompoundscontainantifreezematerials,suchasglycol-typethickeners,inhibitors,andadditives.Synthetic-basefluidshavebothadvantagesanddisadvantages.Someoftheadvanta
