液压制动控制阀斯图特贝克信息.pptx

ObjectiveswIdentify purpose of metering valvewIdentify purpose of proportioning valvewIdentify purpose of pressure differential valvewExplain operation of height sensing proportioning valvewIdentify Operation of combination valveIntroductionBrake hydraulic systems need various type of control devicesBraking performance must be even and consistentCombination disc/drum systems require different type of valvesMetering ValvePurpose of ValveLocation/construction of metering valveOperation of metering valveBleeding system with a metering valveMetering ValvewDelays application of front discs slightlywLocated between master cylinder and front disc brakes(pg 100C)wOperationnValve is held open by springnCloses at 3 30 psinOpens at 75 300 psiwOperation happens in microseconds Proportioning ValveProportioning valve balances pressure on front disc,rear drum vehiclesRestricts fluid to the rear brakesLocated between MC and rear brakes(pg 100C)Split point is the pressure when P.V.closes Slope is percentage of rear pressure to total pressureTwo proportioning valves required on diagonal split systemSome 4 wheel disc brake cars have two Proportioning valvesPage 104 105CHeight Sensing Proportioning ValveUsed on trucks and some carsReduces pressure to rear brakes for light loadsTwo types of valveslinkage type(pg 107C)Gravity ball(pg 108C)Placement of valves Height/Load Sensing ValvewSome systems use one valve per rear wheel.Pressure Differential ValveHydraulically operated switchLocated between front and rear systemsSome systems use a low fluid level switch instead of a pressure Diff SwitchCombination ValveCombines 2 or 3 functionsMetering valveWarning switchProportioning valve Pg 111C3 Function Combination ValveHydraulic System BleedingBrake Bleeding and Bleeder ScrewswMust remove all air from systemwFive methodsnManual bleedingnPressure bleedingnVacuum bleedingnGravity bleedingnSurge bleedingSymptoms of Trapped AirwLow and Spongy when first appliedwRepeated pedal pumping will make pedal become firmwCan be similar to drum brakes in need of adjustmentwCan perform air entrapment test to verify air in systemAir Entrapment TestwWear safety glasseswPump brake 10 to 20 times rapidlywHold pedal pressurewObserve reservoirswLet off pedalwIf air in system,air will squirt fluidBleeding ProcedureswMust follow bleeding sequence and procedures (pg 137L)wBench bleed master cylinder firstwStart at high points in systemwThen,continue from farthest point away from MC and work back towards MC.wWatch fluid level!wUse jar and hose to observe fluidFrozen Bleeder ScrewwUse six sided wrench or socketwAlways test bleeders first when doing brake workwSometimes a hammer will break bleeder freewSometimes use applied heatwTapping on caliper will also free air bubblesMetering Valve prepwMust hold open valve when pressure bleedingwSeveral tools availableWheel Brake Bleeding SequencePressure Bleeding Set UpBrake Hydraulic System ServiceManufacturers RecommendationsFollow brake inspection scheduleFollow service proceduresProblems of FlushingSystem should be refilled with fresh fluidIntervals are 15,000 to 60,000 milesBe careful of stirring sludge up in system!Recentering a Pressure Differential ValveAfter flushing or work on brake system valve becomes off centerMake sure other sources not turning on lightMust determine type of Pressure Differential ValveValve may be separate or part of M.C.Re-centering Single Piston Valve with centering springsRe-centering single piston valve without centering springsRe-centering Two Piston Valve with Centering SpringsServicing Hydraulic System ValvesMetering ValvesBrake problems caused by bad metering valveCan allow front brakes to lock prematurelyTesting metering valveInspect boot for leakageMetering valve pressure test(2 methods)1.Apply brakes and feel stem 2.Pressurize system over 40 psi and open front bleeder to see if system fluid flows(should not flow)Proportioning ValveBrake problems caused by bad proportioning valveMay cause rear drum lock upTesting proportioning valveCheck for leaksCheck“split point”pressure operation(pg 171L)Servicing of proportioning valveCan only overhaul non integral valvesPg 171LHeight Sensing Proportioning ValveBrake problems caused by bad valveCan cause over braking or reduced brakingChassis modificationsAdjustment of valveFollow factory proceduresRemoval and replacement of valveRoad test to make sure correct operationPg 174L