THEORY OF OPERATION - CONTINUED
STEERING SYSTEM - CONTINUED
Low Pressure Standby.
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 work tools piston pump produces flow, system pressure begins to increase because oil flow is blocked at
bank valves. When pilot and steering system piston pump produces flow, system pressure begins to increase
because oil flow is blocked at steering metering pump. Pilot system does not contain a load signal circuit.
Blocked oil creates pressure which is felt at end of flow compensator spool, moving it 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 slight
Piston pump produces enough flow to compensate for normal system leakage when swashplate is at a slight angle.
Also, piston pump has sufficient pressure to provide instantaneous response when a work tool or steering metering
pump is activated.
If there is no flow demand from a hydraulic circuit for work tool or steering metering pump, no load sensing signal
Pressure at pump outlet must only overcome force of margin spring. Pressure at pump outlet is called "low pres-
sure standby". For work tools piston pump low pressure standby is approximately 285 ± 35 psi (1,965 ± 241 kPa).
For pilot and steering system piston pump, low pressure standby is approximately 590 ± 30 psi (4,068 ± 207 kPa).
Low pressure standby is higher than margin pressure due to a higher back pressure created by oil blocked at closed
center valves when valves are in HOLD position.
When piston pump is at low pressure standby, supply oil from pump outlet pushes flow compensator spool left.
This further compresses margin spring. An increased amount of supply oil from pump outlet flows to actuator pis-
ton. This slightly destrokes piston pump.