THEORY OF OPERATION - CONTINUED
HYDRAULIC 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 supply oil 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 will cause piston pump to upstroke.
If pressure of supply oil from pump outlet is high enough, pressure compensator spool is forced left
against cutoff spring.
Movement of pressure compensator spool blocks actuator piston oil 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.
Maximum system pressure is adjusted by turning adjustment screw for pressure compensator spool.