IMPLEMENT AND STEERING HYDRAULIC SYSTEM CONTINUED
Destroking means that the pump is decreasing the displacement (output) and occurs when the signal oil pressure
decreases from lower loads. Destroking also occurs when all of the control valves are in the HOLD position and
signal oil pressure decreases to 0 psi (0 kPa). The lower signal oil pressure in the chamber causes the higher
system oil pressure in the chamber to move the margin spool to the right. The spool movement allows the system
oil pressure to flow through passages and to the large actuator piston. The force that is created by the system oil
pressure (that is behind large actuator piston) is now higher than the force of the actuator spring, and the system
oil pressure (that is behind small actuator piston). The angle of the swashplate decreases.
Pump output decreases until the pump flow is not adequate to maintain system pressure, and system pressure
decreases. When system pressure approaches 305 psi (2,100 kPa) (margin pressure) above the signal oil
pressure, the margin spool moves to the left, and the spool begins to meter oil at the large actuator piston to case
drain. When system pressure approaches 525 psi (3,600 kPa) (low pressure standby), the margin spool moves to
the left and the spool begins to meter oil at the large actuator piston to the case drain. Signal oil pressure is zero
when the control valves are in the HOLD position. The swashplate increases the angle slightly, so that the pump
output makes up system leakage. Also, the higher swashplate angle maintains the margin pressure in the system.
Figure 14. Pump and Compensator Operation (Destroking).