Chapter
Load-Sensing
Pressure-
Compensating (LSPC)
Hydraulic Systems
Copyright Goodheart-Willcox Co., Inc. 417
Objectives
After studying this chapter, you will be able to:
✓ List the two different types of pre-spool-
compensated LSPC systems.
✓ Explain the operation of a fi xed-displacement
LSPC hydraulic system.
✓ Describe the operation of a signal network.
✓ Defi ne load sensing.
✓ Explain the two different meanings of
pressure compensation in an LSPC system.
✓ List examples of fi xed-displacement LSPC
systems in mobile machinery.
✓ Explain the similarities between unloading
valves and fl ow control valves; and pressure
relief valves and pressure compensator valves
within LSPC systems.
✓ Explain the operation of a variable-
displacement LSPC hydraulic system.
✓ Describe examples of relief valves and the
absence of relief valves in LSPC systems.
✓ Explain the benefi t and operation of torque-
limiting controls.
✓ Describe the application of jammer solenoids
in variable-displacement LSPC systems.
✓ Explain what equipment is needed to add
power beyond in an LSPC system.
✓ List all three items that must receive oil from
the primary shuttle valve when a DCV uses a
detent kick-out.
✓ List the advantages and disadvantages of a
variable-displacement LSPC system.
Introduction to Load-Sensing
Pressure-Compensating
(LSPC) Hydraulic Systems
The previous chapter focused on pressure-
compensating hydraulic systems, which use a
variable-displacement hydraulic pump that main-
tains high pressure and practically no fl ow any-
time the DCVs are in a neutral position. LSPC
systems use closed-center DCVs and one of two
hydraulic pump designs:
• Variable-displacement with variable fl ow.
• Fixed-displacement with constant fl ow.
In order to fully understand LSPC systems, it
is helpful to break the system into two separate
operations: load sensing and pressure compensa-
tion. This chapter will begin by explaining load
sensing and pressure compensation separately
in order to build a foundation to better under-
stand the principles of load-sensing pressure-
compensating (LSPC) systems.