THEORY OF OPERATION - CONTINUED
HYDRAULIC SYSTEM - CONTINUED
Low Pressure Standby.
When implements piston pump produces flow, system pressure begins to increase because oil flow is
blocked at bank valves. Blocked oil creates pressure which is felt at end of flow compensator spool. Flow
compensator spool moves left against margin spring. This permits system oil to flow to actuator piston.
When pressure on actuator piston increases, force of bias spring is overcome and swashplate is moved to a
Piston pump produces enough flow to compensate for normal system leakage when swashplate is at a min-
imum angle. Also, piston pump has sufficient pressure to provide instantaneous response when an imple-
ment is activated.
If there is no flow demand from a hydraulic circuit for implements, no load sensing signal is generated.
Pressure at pump outlet must only overcome force of margin spring. Pressure at pump outlet is called "low
pressure standby". For implements piston pump, low pressure standby is approximately 290 ± 30 psi
(1,999 ± 207 kPa).
Low pressure standby is higher than margin pressure due to a higher back pressure created by oil which is
blocked at closed center valves when valves are in HOLD position.
N OT E
Amount of system leakage and adjustments to the flow compensator spool can cause margin pressure to
equal low pressure standby. Margin pressure can never be higher than low pressure standby.
When piston pump is at low pressure standby, supply oil from pump outlet pushes flow compensator spool
left. This will further compress margin spring. An increased amount of supply oil from pump outlet will
flow to actuator piston. This will slightly destroke piston pump.