THEORY OF OPERATION - CONTINUED
STEERING SYSTEM - CONTINUED
N OT E
Load sensing signal pressure does not need to increase in order to upstroke piston pump.
When a hydraulic circuit for work tool or steering system requires flow, pressure from pump outlet is reduced.
Reduced pump output pressure causes force from pump outlet pressure to decrease relative to force from load
sensing signal and margin spring. This force is on left side of flow compensator spool. Force is greater than pump
supply pressure at right of spool.
Spool moves right which blocks oil flow to actuator piston. Oil in chamber for actuator piston is vented to case
drain across flow compensator spool. This allows bias spring to move swashplate to a greater angle.
Pump now produces more flow. This condition is known as "upstroking".
These conditions can result in upstroking pump:
If a hydraulic circuit for work tool or steering system is initially activated from low pressure standby, load
sensing signal increases pump output flow. This increased pump output flow is routed to position of a con-
trol valve main control spool that demands oil.
Piston pump upstrokes when demand increases from changing position of control valve main control
spool, or when hand metering unit is turned at a faster rate of speed.
If another hydraulic circuit for work tool is engaged, there is a need for increased pump flow.
If flow demand on hydraulic system remains constant, piston pump will upstroke when engine speed