Copyright Goodheart-Willcox Co., Inc.
Chapter 18 Load-Sensing Pressure-Compensating (LSPC) Hydraulic Systems 437
If the variable-displacement pump uses a bias piston instead of a bias
spring, the control piston will have a larger surface area, and it might be called
the large piston. The control piston must be larger than the bias piston in this
style pump because pump output pressure acts on both piston surfaces any-
time the pump compensator is trying to destroke the pump. In this situation,
the control piston’s larger surface area must produce a stronger force to over-
come the bias piston’s force.
Working Mode
Whenever the operator actuates a DCV to request oil fl ow, the pump gen-
erates oil fl ow to perform some work. The DCV must be a load-sensing valve,
meaning that as the oil is routed to the cylinder, the load-sensing DCV must
also send a signal pressure to the pump’s compensator so the pump can meet
the system’s demands. See the schematic in Figure 18-17.
Figure 18-16. An inline axial LSPC piston pump uses a flow control spool for directing oil to the control piston to
destroke the variable-displacement pump while in the low-pressure standby mode. The control piston extends against
the swash plate, pushing the swash plate slightly against the resistance of the bias spring. Note the smaller charge
pump used to provide low-pressure fluid to the axial piston pump.
Bias spring
Swash
plate
DCV
Control piston
Axial piston
Axial piston
Flow control
spool (300 psi)
Charge
pump
Pressure
compensator
spool (2500 psi)
Shuttle valve