THEORY OF OPERATION - CONTINUED
HYDRAULIC SYSTEM - CONTINUED
When a hydraulic circuit for implements requires flow, pressure from pump outlet is reduced. Reduced
pump output pressure causes force from pump outlet 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 that is in actuator piston chamber is vented
to case drain across flow compensator spool. This allows bias spring to move swashplate to a greater
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 a hydraulic circuit for an implement is initially activated from low pressure standby, load sensing
signal increases pump output flow. This increased pump output flow is routed to position of control
valve main control spool that demands oil.
(b) Piston pump will upstroke when flow demand increases from changing position of control valve main
(c) When another hydraulic circuit for implements is engaged, there is a need for increased pump flow.
(d) If flow demand on hydraulic system remains constant, piston pump will upstroke when engine speed