THEORY OF OPERATION - CONTINUED
STEERING SYSTEM - CONTINUED
High Pressure Stall.
Pressure compensator spool is parallel with flow compensator spool. Pressure compensator spool limits maximum
system pressure at any pump displacement.
Pressure compensator spool is forced right by cutoff spring during normal operation.
If piston pump is at a high pressure stall or maximum system pressure, pressure of load sensing signal is equal to
pressure of oil supply from pump outlet.
Combined pressure of load sensing signal and margin spring forces flow compensator spool right. When flow
compensator spool moves right, a passage will normally be opened. This allows oil holding actuator piston to be
vented to case drain. This causes piston pump to upstroke.
If supply oil pressure from pump outlet is high enough, pressure compensator spool is forced left against cutoff
Movement of pressure compensator spool blocks oil from actuator piston from flowing to case drain. This allows
supply oil to flow to actuator piston.
Increase in pressure on actuator piston overcomes force of bias spring. Swashplate moves and piston pump
Piston pump is now at minimum flow and supply oil at pump outlet pressure is at maximum pressure. These condi-
tions are maintained for a single work tool in a stall condition.
Maximum system pressure is adjusted by turning adjustment screw for pressure compensator spool.
If multiple work tool hydraulic circuits are activated, work tool piston pump circuits still produce flow while one
circuit is at a high pressure stall. This flow meets other circuits needs that are operating at a lower work port pres-
sure. Piston pump could be producing maximum flow while pressure of supply oil from pump outlet is at maxi-