Chapter3HydraulicPumps

Chapterlist3.1Introduction

3.2PistonPumps

3.3VanePumps

3.4GearPumps

3.1

Introduction

3.1.1OperatingPrinciple

3.1.2Mainperformanceparametersinhydraulicpumps

3.1.3Performancecurves

3.1.4Classification

3.1.5Graphicsymbols

3.1.1

Operatingprinciple

Hydraulicpumpsconvertmechanicalenergyintohydraulicenergy.Theysupplyfluidtothecomponentsinthehydraulicsystem.

1,2-Non-returnvalve3-Spring4-Cylinder5-Piston6-EccentricwheelFig.3-1Operatingprincipledisplacementpumps

Theoperatingprincipleofeverypumpinahydraulicsystemdependsuponthealternativechangeoftheirworkingvolumes.

Note:

thepistondiameterasd,theoffsetoftheeccentricwheelase,thelongeststrokethepistoncanreachass

andthedischargedoilvolumeV,then

Asdescribedabove,thebasicconditionsthatconstituteahydraulicpumpcanbeconcludedasfollows:

1)Oiltightchamber.

2)Flow-deploying(separatethelowpressurefromthehighone).

3)Theabsoluteoilpressureinthereservoirshouldbeequalormorethantheatmosphericpressure.3.1.2Mainperformanceparametersinhydraulicpumps

1.Pressure

（1)

Suctionpressure——thepressureintheinletport.Forself-primingsuctionpumps,thesuctionpressureislowerthantheatmosphericpressure.

（2)

WorkingpressureP——theoutletpressurewhenthehydraulicpumpisinoperation,whichdependsupontheoverallloads.

（3)

RatedpressurePS——thehighestpressuretestedwithstandardmethodwhenthepumprotatescontinuouslyundercommonworkingconditions.2.Delivery,flowrateandvolumetricefficiency

(1)DeliveryV

（2）Flowrate

Theflowrateconsistsoftheaveragetheoreticalflowrate,thepracticalflowrateandtheinstantaneoustheoreticalflowrate.

Averagetheoreticalflowrateqt

Practicalflowrate

q

Instantaneoustheoreticalflowrate

qsh

Ratedflowrate

qs3.Powerandefficiency

(1)Inputpower

pr

(2)Outputpower

P

(3)Volumetricefficiency

ηv

(4)Mechanicalefficiency

ηm(5)Overallefficiencyηandmechanicalefficiency

ηm

4.Rotatingspeed

(1)Ratedrotatingspeed

ns

：

thehighestrotatingspeedfornormalcontinuousandlong-timeoperationunderratedpressure.(2)Highestrotatingspeed

nmax：

thehighestrotatingspeedforshort-timeoperationunderratedpressure,whichmaybehigherthanns.(3)Lowestspeed

nmin：

thelowestspeedofthepumpfornormaloperation.(4)Rangeofrotatingspeed

：

thespeedrangebetweennminandnmax.3.1.3Performancecurves

Fig.3-2showsaperformancecurveofahydraulicpump,inwhichtheabscissarepresentsworkingpressurepofthehydraulicpumpandtheordinatethevolumetricefficiencyηv

(orthepracticalflowrateq),overallefficiencyηandinputpowerＰr.Fig.3-2Performancecurvesofhydraulicpumps

Forsomehydraulicpumpswithcertainrotatingspeedrangesorvariabledisplacementcapacity,theformatofthegeneralcharacteristiccurvesshowninFig.3-3arecommonlyusedtoreflectalltheirperformances.Theabscissarepresentstheworkingpressurepofthepumpandtheordinaterepresentsthepump’sflowrateq,rotatingspeednordeliveryV.Fig.3-3alsoshowstheequalefficiencycurveηv,andtheequalpowercurveＰri.Fig.3-3Generalperformancecurvesofhydraulicpumps

3.1.4Classification

Hydraulicpumpsmaybeclassifiedbytheformsofmainmovingcomponentsandtheirmovingmanners:gear,vane,pistonandscrewpumps.

1)Gearpumpsmaybefurtherclassifiedintwobroadcategories,externalorinternalmesh;

2)Vanepumpsmaybefurtherdividedintodouble-actingvanepumps,single-actingvanepumpsandcam-rotorvanepumps;

3)Pistonpumpsconsistofradialpistonpumpsandaxialpistonpumps;

4)Screwpumpsincludesingle-screwpumps,two-screwpumpsandthree-screwpumps.Hydraulicpumpsmaybefurtherclassifiedaccordingtothetypesofdelivery:(1)Fixeddelivery;(2)Variable

delivery.

variabledeliverycanbeaccomplishedinsingle-actingvanepumps,radialoraxialpistonpumps.3.1.5

Graphicsymbols

ThegraphicsymbolsofhydraulicpumpsareshowninFig.3-4.Fig.3-4Graphicsymbols

a)Non-returnfixeddeliveryhydraulicpumpsb)Non-returnvariabledeliveryhydraulicpumpsc)Reversiblefixeddeliverypumpd)Reversiblevariabledeliverypump

3.2PistonPumps3.2.1Valveshaftradialpistonpumps

3.2.2Swashplateaxialpistonpumps3.2.3Bentaxisaxialpistonpumps

3.2.1Valveshaftradialpistonpumps

Theoilsuctionanddeliveryactionsofapistonpumpdependuponthesizechangeofthechamberproducedbythereciprocatingmovementofthepistonswithintheircylinderbores.ThesignalpistonpumpshowninFig.3-1isaradicaltype.1.OperatingprincipleThepump’sdeliveryisexpressedby:

wheredisthepistondiameter,eistheoffsetbetweenthestatorandcylindercase(rotor),zisthenumberofthepistons.Fig.3-5Valveshaftradialpistonpump1-Piston2-Rotor3-Bush4-Stator5-Valveshaft2.Structurefeatures

1)Theinletandtheoutletportsofthevalveshaftareseparatedbyacenterlandandbalancinggroovesaresetintheiroppositedirections.Thehydraulicradialforcesactingonthevalveshaftarebalancedoutbythebalancinggrooves.2)Thedeliveryofthepumpcanbechangedsimplybychangingtheeccentricityeofthestatorwithrespecttotherotor;whiletheinletandoutletdirectionscanbechangedbychangingthedirectionofe(i.e.,ebecomesnegativefrompositive).3.Radialpistonpumpswithload-sensitivevariabledisplacementcapacity

Fig.3-6OperatingprincipleofLoad-sensitivevariabledischargesofradialpistonpump1-Rightvariablepiston2-Rotor3-Stator4-Leftvariablepiston

3.2.2Swashplateaxialpistonpumps

1.Operatingprinciple

Fig.3-7Swashplateaxialpistonpump

1-Swashplate2-Piston3-Cylinder4-Transmissionshaft5-Valveplate6-Pin7-Adjustingpiston8-Bolt9-Screw10-Handwheela-Inletportb-Outletport

Theswashplateaxialpistonpumpisalsocalledstraightshaftaxialpistonpump.Notethediameterofthepistonasd,thediameterofthecylinderboredistributioncircleasD,thepistonnumberasz,theangleoftheswashplatewithrespecttothepistonaxisasβ,thenthedeliveryoftheswashplateaxialpistonpumpis:

(3-2)

Notetheverticaldistancebetweenthepin(forceapplyingpoint)andtheswashplategyrationcenterlineasL,then

tanβmax=smax/LBecausethedisplacementofthepinequalsthatoftheadjustingpiston,thentanβ=s/L,substitutingitintoformula3-2,wehave:

(3-3)

Fromformula3-3,wecanseethatthepumpdeliveryisproportionaltothepump’sdisplacement.Tolimitthehydraulicsideforcesonthepistons,theswashplatelargestangleβmaxshouldbelessthan18°～20°.2.Structurefeatures

1)

Forpistonpumps,themachiningaccuracybetweenthepistonsandthecylinderboresiseasytoacquire;andtheycanreachhighvolumetricefficiency;highratedpressure(highupto32MPa).2)

Toavoidpressurepulsationattheendsofpistons(tightvolumes)whereoilpressurearechangedfromsuctiontodelivery,dampinggrooves(orholes)aresetinthefrontendsofthesuctionanddeliveryportsofvalveplate,orthevalveplateisplacedananglealongthecylinderrotatingdirection.

3)

Leakagepasttheclearanceamongthepistons,pistonshoesandcylinderblockfacearecarriedthroughthepumpbodyandoutacasedrainconnectiontothereservoir,whichcarriesawaytheheatgeneratedandpreventsanyheatbuildupandoverheatingwithinthepump.4)Theflowpulsationinapumpwithoddnumberpistonsislowerthanonewithevennumberbytheory,thuspistonpumpsalwayshaveanoddnumberofpistons,usually5,7or9.3.2.3Bent-axisaxialpistonpumps

1.Operatingprinciple

Fig.3-8Bent-axisaxialpistonpump

1-Valveplate2-Piston3-Cylinder4-Pistonrod5-Transmissionshafta-Inletportb-Outletport2.Constantpowervariabledisplacementbent-axisaxialpistonpump

Fig.3-9Constantpowervariabledisplacementbent-axisaxialpistonpump

1-Cylinder2-Swashplate3-Piston4-Valveplate5-Pin6-Dampingorifice7-Controlpiston8-Springplate9、10、12-Spring11-Servovalve13-Variabledisplacementpiston

3.3VanePumps3.3.1Double-actingVanePumps3.3.2Single-actingvanepumps

Vanepumpsmaybeeitherofthesingle-actingordouble-actingtype.Theformerisusedforvariabledisplacementpumps,whilethelatterforfixeddisplacementpumps.1.Operatingprinciple

Fig.3-10Double-actingVanePump

3.3.1Double-actingVanePumps

Thedouble-actingvanepumpgetsitsnamefromthefactthattherearetwoinletsegmentsandtwooutletsegmentsduringeachrevolution.1,11-Bearing2,6-Leftandrightvalveplate3,7-Frontandrearhousing4-Vane5-Stator8-Endcover9-Transmissionshaft10-Dustproofring12-Screw13-RotorFig.3-11a)Operatingprincipleofdouble-actingvanepumpb)Springvaneconfiguration

1,2,3,4,5,6,7,8,15-Vane10,12-Inletport9,11-Outletport13-Rotor14-Spring16-Stator2.Structurefeatures

1）Simplicity:becausethetwoinletsegmentsandthetwooutletsegmentsaredesignedsymmetricallyonthevalveplate,thepressureforcesactingontherotorandthecamringareequalandopposite,completelycancelingeachotherout.Asaresult,asmallradialforceactsonthebearings.Consequently,thelifeofthistypeofpumpisexceptionallygood.

2）Intravanefeature:

manyofthebalancedvanepumpsalsohaveanintravanefeaturewhichhelpstokeepthevaneincontinuouscontactwiththeinnerringduringtherisesandfallswhilealsominimizingvane-tipcontactforces.Toreachthis,thevane-tipsofthevanegroovesindouble-actingvanepumpsareusuallyconnectwithoutletport.ThedeliveryVfordouble-actingvanepumpis(3-4)3)Constantdelivery

Pumpingoccurswhileonevaneisincontactwiththemajordwellandonewiththeminordwellofthecamring.Eachdwellisessentiallyaconstantradiussothefluiddeliveredperdegreeofrotationisaconstantvalue.Asaresult,theflowdeliveredbyabalancevanepumpisverysmoothcomparedtomostothertypesofpumpingmechanisms,andsoundlevelsareinherentlylow.4)Optimize

Besidessuitablematerialchooseandheattreatment,wewouldtakesomemeasurestosolvetheproblemofpressure-unloadedinordertoenhancetheoperationpressureforthedoubleactionvanepump.Usuallytherearethreekinds:doublevanes,springvaneandmother-sonvaneconfiguration.3.3.2

Single-actingvanepumps

Thesingle-actingvanepumpgetsitsnamefromthefactthatthereareonlyoneinletsegmentandaseparateoutletsegmentduringeachrevolution.1.OperatingprincipleFig.3-12OperatingprincipleofSingle-actingvanepumpThedeliveryVforsingle-actingvanepumpis(3-5)

1-Stato2-Rotor3-vaneA-InletportB-Outletport

2.

Pressure-limitingvariablevanepumpsFig.3-13YBXtypeexternalfeedbackpressure-limitingvariablevanepump

1-Preloadadjustingscrew2-Pressurecontrolspring3-Pumpbody4-Springplate5-Rotor6-Stator7-Slidingblock8-Transmissionshaft9-Vanes10-Feedbackpiston11-AdjustingscrewformaximumflowrateFig.3-14Pressure-limitingvariablevanepumpoperation

a)Simplifiedpressure-limitingvariablevanepumpoperationb)Pressure-flowcharacteristicscurve1-Stator2-Pressurecontrolspring3-Preloadadjustingscrew4-Rotor5-Piston6-Eccentricityadjustingscrew3.4GearPumps3.4.1Externalmeshgear

pumps3.4.2Innermeshgearpumps3.4.3

Screwpump

3.4.1Externalmeshgear

pumpsAccordingtomeshingtypes,therearetwotypesofgearpumps:externalgearandinternalgear.1.Operatingprinciple

Fig.3-15CB-Btypeexternalgearpumpconstruction

1-Rearcover2-Needlerollerbearing3-Pumpbody4-Drivepump5-Frontcover6-Transmissionshaft7-Key8-Drivengear

Fig.3-16Externalgearpumpoperation

1-Pumpbody2-Drivegear3-Drivengear

Notetheinstantaneousmaximumflowasqmax，theminimumasqmin，andtheaverageasqp，thentheinstantaneousflowfluctuatingcoefficientisexpressedby：

(3-6)

increasesinverselywiththenumberofgears.

Thedeliverycanbeobtainedfromtheformulathatdescribestheareaoftoothvalveforagear:A=πm2：

(3-7)

Fromformula(3-7),wecanseethatthedeliveryVisproportionaltothegearteethnumber(z)andthesquareofitsmodulus(m2).So,whenthediameterofgearpitchcircleDj=mzisgiven,thedeliveryofthepumpcanbeincreasedbyincreasingthemodulus

mordecreasingthegearteethnumberz.Itisforthisreasonthatthenumberofgearteethisusuallyfewer,andthegearshouldbemodifiedtoavoidrootundercutduetosmallteethnumberofgear.Structurefeatures

（1）Lowsoundlevel

（2）Leakage

（3）Clearancecompensation.Fig.3-17isahighpressuregearpumpwithafloatingaxissets.

Fig.3-17Themiddleandhighpressuregearpumpwithfloatingbushing1,2-floatingbushing（4）

Unbalancedforce:theresultanthydraulicpressureonthegearsandtheshaftisunbalancedduetothepressuredifferentialbetweentheinletandtheoutletports,seeFig.3-18a.Fig.3-18aUnbalancedforce

Theunbalancedradialhydraulicradialpressurecanbeexpressedby:(3-8)

Asdescribedabove,whenthesizeofthepumpisgiven,thehighertheoilpressure,thelargertheradialunbalancedforce.Thehydraulicradialforceactingonthegearshaftnotonlyaffectsthelifeofthebearings,butalsodistortsthegearshaft,resultinginthegeartip’sscrapingagainsttheinnercontourofthepumpbody.Measurestobalancethehydraulicradialforce:1)Settingbalancinggrooves2)Reducingtheareaoftheoutletports

（5）Phenomenonofsurroundedoilandloadreliefmeasures

1)

Phenomenonofsurroundedoil

Fig.3-19