Basic Hydraulic Systems.docx
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Basic Hydraulic Systems.docx
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BasicHydraulicSystems
SUBCOURSEEDITION
AL0926A
BASIC
HYDRAULICSYSTEMS
ANDCOMPONENTS
BASICHYDRAULICSYSTEMSANDCOMPONENTS
SubcourseNumberAL0926
EDITIONA
USArmyAviationLogisticsSchool
FortEustis,Virginia23604-5439
4CreditHours
EditionDate:
September1994
SUBCOURSEOVERVIEW
Thissubcourseisdesignedtoprovideinstructionontheconceptandoperationofthebasiccomponentsofthehydraulicsystem.Italsodescribesthevariouscomponentsofatypicalhydraulicsystem,theirconstructionandfunctions,andtheirrelationshiptoeachother.
Whenthetermhydraulicsisappliedtoaircraft,itmeansamethodoftransmittingpowerfromonelocationtoanotherthroughtheuseofaconfinedfluid.Thefunctionsperformedbyhydraulicsystemsinaircraftincludeassistinginflightcontrol,extendingandretractinglandinggear,positioningflaps,operatinghoists,raisingandloweringcargodoors,andstartingengines.
ThehydraulicsystemsusedinArmyaircraftaredependableandrelativelytrouble-free.Themaintenancerequirementsaresmallincomparisontotheworkthesystemperforms.
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Thissubcourseistobecompletedonaself-studybasis.Youwillgradeyourlessonsasyoucompletethemusingthelessonanswerkeyswhichareenclosed.Ifyouhaveansweredanyquestionincorrectly,studythequestionreferenceshownontheanswerkeyandevaluateallpossiblesolutions.
Therearenoprerequisitesforthissubcourse.
Thissubcoursereflectsthedoctrinewhichwascurrentatthetimeitwasprepared.Inyourownworksituation,alwaysrefertothelatestofficialpublications.
Unlessotherwisestated,themasculinegenderofsingularpronounsisusedtorefertobothmenandwomen.
TERMINALLEARNINGOBJECTIVE
ACTION:
Youwilldemonstrateaknowledgeofthebasiccomponentsofthehydraulicsystem,includingthedeviceswhichactuate,discharge,andcontroltheflowofhydraulicfluidandthosedeviceswhichsense,control,andlimithydraulicpressure.
CONDITIONS:
Youwillusethematerialinthissubcourse.
STANDARD:
Youmustcorrectlyanswer70percentofthequestionsonthesubcourseexaminationtopassthissubcourse.
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TABLEOFCONTENTS
SectionPage
SubcourseOverviewi
TerminalLearningObjectiveii
AdministrativeInstructionsiv
GradingandCertificationInstructionsiv
Lesson1:
HydraulicReservoirs,Filters,Pumps,
Accumulators,andMotors1
PracticeExercise19
AnswerKeyandFeedback22
Lesson2:
BasicConstructionandOperationofHydraulic
ActuatingDevices,FlowControl,andDirectional
Devices25
PracticeExercise43
AnswerKeyandFeedback46
Lesson3:
HydraulicPressure-Limiting,Controlling,and
SensingDevices49
PracticeExercise55
AnswerKeyandFeedback58
Examination61
Appendix:
Glossary69
StudentInquirySheets
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GRADINGANDCERTIFICATIONINSTRUCTIONS
Examination:
Thissubcoursecontainsamultiple-choiceexaminationcoveringthematerialcontainedinthissubcourse.Afterstudyingthelessonsandworkingthroughthepracticeexercises,completetheexamination.Markyouranswersinthesubcoursebooklet,thentransferthemtotheACCPExaminationResponseSheet.Completelyblackouttheletteredovalwhichcorrespondstoyourselection(A,B,C,orD).Useanumber2leadpenciltomarkyourresponses.WhenyoucompletetheACCPexaminationresponsesheet,mailitinthepreaddressedenvelopeyoureceivedwiththissubcourse.Youwillreceiveanexaminationscoreinthemail.YouwillreceiveFourcredithoursforsuccessfulcompletionofthisexamination.
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LESSON1
HYDRAULICRESERVOIRS,FILTERS,PUMPS,ACCUMULATORS,ANDMOTORS
STPTasks:
552-758-1063
552-758-1071
OVERVIEW
LESSONDESCRIPTION:
Inthislessonyouwilllearnthebasicoperationofthehydraulicreservoirs,filters,pumps,accumulators,andmotors.
TERMINALLEARNINGOBJECTIVE:
ACTION:
Afterthislessonyouwilldemonstrateknowledgeofhydraulicreservoirs,filters,pumps,accumulators,andmotors.
CONDITIONS:
Youwillstudythematerialinthislessoninaclassroomenvironmentoratyourhome.
STANDARD:
Youwillcorrectlyanswerallthequestionsinthepracticeexercisebeforeyouproceedtothenextlesson.
REFERENCES:
Thematerialcontainedinthislessonwasderivedfromthefollowingpublications:
AR310-25,AR310-50,FM1-500,FM1-509,TM1-1500-204-23Series,TM55-1510-Series(FixedWingMaintenanceManuals),TM55-1520-Series(RotarywingMaintenanceManuals)andTM4301A050267(AirForce)
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INTRODUCTION
Ameansofstoringhydraulicfluidandminimizingcontaminationisnecessarytoanyaircrafthydraulicsystem.Thesefunctionsareperformedbyreservoirsandfilters.Thecomponentwhichcausesfluidflowinahydraulicsystem--theheartofanyhydraulicsystem--canbeahandpump,power-drivenpump,accumulator,oranycombinationofthethree.Finally,ameansofconvertinghydraulicpressuretomechanicalrotationissometimesnecessary,andthisisaccomplishedbyahydraulicmotor.
HYDRAULICRESERVOIRS
Thehydraulicreservoirisacontainerforholdingthefluidrequiredtosupplythesystem,includingareservetocoveranylossesfromminorleakageandevaporation.Thereservoircanbedesignedtoprovidespaceforfluidexpansion,permitairentrainedinthefluidtoescape,andtohelpcoolthefluid.Figure1-1showstwotypicalreservoirs.Comparethetworeservoirsitembyitemand,exceptforthefiltersandbypassvalve,noticethesimilarities.
Fillingreservoirstothetopduringservicingleavesnospaceforexpansion.Mostreservoirsaredesignedwiththerimatthefillerneckbelowthetopofthereservoirtopreventoverfilling.Somemeansofcheckingthefluidlevelisusuallyprovidedonareservoir.Thismaybeaglassorplasticsightgage,atube,oradipstick.Hydraulicreservoirsareeitherventedtotheatmosphereorclosedtotheatmosphereandpressurized.Adescriptionofeachtypefollows.
VentedReservoir.Aventedreservoirisonethatisopentoatmosphericpressurethroughaventline.Becauseatmosphericpressureandgravityaretheforceswhichcausethefluidtoflowtothepump,aventedreservoirismountedatthehighestpointinthehydraulicsystem.Airisdrawnintoandexhaustedfromthereservoirthroughaventline.Afilterisusuallyinstalledintheventlinetopreventforeignmaterialfrombeingtakenintothesystem.
PressurizedReservoir.Apressurizedreservoirissealedfromtheatmosphere.Thisreservoirispressurizedeitherbyenginebleedairorbyhydraulicpressureproducedwithinthehydraulicsystemitself.Pressurizedreservoirsareusedonaircraftintendedforhighaltitudeflight,whereatmosphericpressureisnotenoughtocausefluidflowtothepump.
Inreservoirspressurizedbyenginebleedair,theamountofairpressureisdeterminedbyanairpressureregulator--usually10to15poundspersquareinch(psi)gage.Anexampleofa
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hydraulicallypressurizedreservoirusedintheCH-47hydraulicsystemisshowninFigure1-2.
Thisreservoir,ortankasitisreferredtobyBoeing-Vertol,isconstructedofametalhousingwithtwointernalpistons,onefixedandtheotherafloatingpistonwhichslidesalongacentraltube.AttachedtothefloatingpistonisalargertubethatprojectsthroughtheforwardendofthetankandiscalibratedtoindicateFULLandREFILLfluidlevelsforramp-upandramp-downpositions.
Figure1-1.TypicalHydraulicReservoirs.
Hydraulicfluidat3,000psiflowsintothecentraltubeasshowninFigure1-2,passesthroughtwooutletholes,andappliespressureatthepistonareabetweenthetwotubes.Becausethesmallerpistonhasa.5-square-inch(sqin)exposedsurfaceandthefloatingpistonhasa30-sq-inexposedsurface,the3,000-psipressureactinguponthesmallerforwardareaproducesanopposingpressureof50psionthereturnfluidstoredattherearofthepiston.
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AdditionalReservoirComponents.Manyreservoirs,asshowninFigure1-1,areconstructedwithbafflesorfinstokeepthefluidfromswirlingandfoaming.Foamingcancauseairtobecomeentrainedinthesystem.
Filtersareincorporatedinsomereservoirstofilterthefluidbeforeitleavesthereservoir.
Abypassvalveisusedtoensurethatthepumpdoesnotstarveifthefilterbecomesclogged.
Astandpipeisusedinareservoirwhichsuppliesanormalandanemergencysystem.Themainsystemdrawsitsfluidfromthestandpipe,whichislocatedatahigherelevation.Thisensuresanadequatefluidsupplytothesecondarysystemifthemainsystemfails.
Figure1-2.HydraulicReservoirPressurizedWithHydraulicFluid.
HYDRAULICFILTER
Contaminationofhydraulicfluidisoneofthecommoncausesofhydraulicsystemtroubles.Installingfilterunitsinthepressureandreturnlinesofahydraulicsystemallows
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contaminationtoberemovedfromthefluidbeforeitreachesthevariousoperatingcomponents.Filtersofthistypearereferredtoaslinefilters.
LineFilterConstruction.AtypicallinefilterisshowninFigure1-3.Ithastwomajorparts--thefiltercase,orbowl,andthefilterhead.Thebowlholdstheheadthatscrewsintoit.Theheadhasaninletport,outletport,andreliefvalve.Normalfluidflowisthroughtheinletport,aroundtheoutsideoftheelement,throughtheelementtotheinnerchamber,andoutthroughtheoutletport.Thebypassvalveletsthefluidbypassthefilterelementifitbecomesclogged.
Figure1-3.TypicalLineFilterAssembly.
TypesofFilterElements.ThemostcommonfilteringelementusedonArmyaircraftisthemicronictype.Itisadisposableunitmadeoftreatedcelluloseandisfor
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