1、Open Center Valve BasicsMobile Valve Training 1Transition ChecksDouble-acting, Parallel, Hold-in-neutral Work SectionsB BA AFixed DisplacementPumpSystemRelief ValveInlet OutletTankOpen CenterPassageParallel PassageTank PassageValve Terms2 Load force feedback - operator feel Responsive function contr
2、ol Flexible circuitry - parallel, series, tandem Few problems with system stability Familiar technology Less sensitive to contamination Simple design Easy to trouble-shoot Low maintenance Low costOpen Center Systems Positive Characteristics 3 Metering band generally load dependant Throttle changes a
3、ffect metering Multi-function inter-action Operator fatigue Non linear lever efforts on manual sections Can be inefficient Wasted horsepower & fuel Heat GenerationOpen Center Systems Application Concerns 4Transition Check IntermediateFeed CoreParallel PathNotchesTank NotchesWork Port “A” Work Port “
4、B”Open Center NotchesParallelPathUpstream open centerDownstreamOpen CenterParallel Valve Work Section5 ConcernLoad Dependent MeteringOpen Center Metering Band051015202530354045500% 10% 20% 30% 40% 50% 60% 70% 80%90% full% of spool strokeFLOWGPM0 load1000 PSI2000 PSIQ=CxAx P6Open Center Spool Forces
5、Flow through the valve creates flow forces that act inconsistently on the spool Bernoulli forces Pressure drop across the notches result in an undesirable force on the spool Undesirable spool forces can occur at any or all of the metering lands/notches Open Center, Parallel Path, & Tank Increased le
6、ver efforts result from forces acting on the spool7Open Center Spool Forces01020304050607080.0 + .1 + .2 + .3 + .4STROKE In.Neutral to “A“A“ to NeutralFORCE#s ConcernBernoulli flow forcesSpring only8Power ConsumptionOpen Center Valve CircuitHP = GPM x PSI / 1714 ConcernCan be inefficient9Open Center Valve Basics ConcernMulti-function interaction Oil takes path of least resistance 10
