THEORY OF OPERATION - CONTINUED
HYDRAULIC SYSTEM - CONTINUED
When steering system hydraulic circuit requires flow, pressure from pump outlet is reduced. Reduced
pump output pressure causes force from pump outlet to decrease. Reduced pressure is 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 flow of oil to actuator piston. Oil in actuator piston chamber 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".
N OT E
Load sensing signal pressure does not need to increase in order to upstroke piston pump.
These conditions can result in upstroking pump:
(a) If steering system is initially activated from low pressure standby, load sensing signal increases pump
output flow. This increased pump output flow is routed to steering circuit and pilot circuit compo-
(b) Piston pump will upstroke when hand metering unit is turned at a faster rate of speed.
(c) If flow demand on hydraulic system remains constant, piston pump will upstroke when engine speed