Copyright Goodheart-Willcox Co., Inc.
Chapter 18 Load-Sensing Pressure-Compensating (LSPC) Hydraulic Systems 435
Note
The flow control spool can also be called the low-pressure standby
spool, flow compensator spool, or the margin spool. In a fixed
displacement LSPC system, the unloading valve takes the place
of the flow control spool.
Figure 18-13. A compensator assembly from an LSPC variable-displacement piston pump uses two spools: a flow
control spool and a pressure compensator spool. The compensator also receives a signal pressure through the
O-ring elbow fitting.
Figure 18-14. Both pump symbols shown within the simple hydraulic motor circuits can be used to depict LSPC
variable-displacement hydraulic pumps. The pump senses the working pressure of the motor. Older Caterpillar
schematics might contain two arrows within the envelope to directly represent the pump compensator spool and
the load-sensing spool.
Flow
control
spool
Pressure
compensator
spool
Flat-face
O-ring elbow
fitting
LSPC variable-displacement
hydraulic pumps