THEORY OF OPERATION - CONTINUED
STEERING SYSTEM - CONTINUED
N OT E
Load sensing signal pressure does not need to decrease in order to destroke piston pump.
When less flow is required, piston pumps destroke. Piston pump destrokes when force at right of flow compensator
spool becomes greater than force at left.
Flow compensator spool moves left, which allows more oil flow to actuator piston. Pressure on actuator piston is
Increased pressure overcomes force of bias spring, which moves swashplate to a reduced angle. When pressure
from pump outlet matches force at left of flow compensator spool, spool returns to a metering position. Piston
pump returns to a constant flow.
These conditions result in destroking piston pump:
A control valve main control spool is moved to HOLD position.
Control valve main control spool is moved to a position that requires less flow.
If multiple control valves are being used, piston pump will destroke when there is a reduction in demand
from any one control valve.
Engine speed increases.
When piston pump destrokes, supply oil pressure from pump outlet decreases on right side of flow compensator
spool. Pressure on left side of flow compensator spool is sum of load sensing signal and margin spring pressures.
Flow compensator spool will meter force on both ends of spool. Once forces become equal on each end of spool,
system will stabilize.