Copyright Goodheart-Willcox Co., Inc.
Chapter 18 Load-Sensing Pressure-Compensating (LSPC) Hydraulic Systems 451
Variable-Displacement LSPC System Advantages
Several decades ago, when hydraulic engineers began to design variable-
displacement LSPC systems, they envisioned a hydraulic system that would
deliver only the “pressure and fl ow” required to do the work and nothing more.
Today, nearly four decades later, manufacturers are still using these systems
on much more complex and expensive machines. LSPC variable-displacement
hydraulic systems have the following advantages:
• The system runs at low pressures (300 to 500 psi [21 to 34 bar]) when
the DCVs are in a neutral position and produces very little fl ow
(perhaps less than 0.5 gpm).
• The hydraulic system uses only a fraction of a horsepower when the
system requires no fl ow.
• With the DCVs are in a neutral position, the system generates very
little heat and very little noise.
• The system can quickly ramp up to deliver hydraulic fl ow and
pressure on demand.
The agricultural industry serves as one of the largest customers for
machines equipped with variable-displacement LSPC hydraulic systems. The
systems are commonly used on large agricultural tractors and some combine
harvesters.
Variable-Displacement LSPC System Disadvantages
LSPC variable-displacement systems do have some disadvantages:
• The system costs more to manufacture than open-center hydraulic
systems and PC systems.
• The system requires a complex signal network of primary and
secondary shuttle valves that sense the highest system working
pressure and send that signal back to the pump compensator.
• Perhaps the largest drawback to LSPC pre-spool compensation systems
is that if an operator requests multiple hydraulic functions at one
time and if that request was for more oil than the pump is capable of
delivering, the actuators with the smallest load will receive the oil fi rst,
while the highest system loads will receive no oil. The next chapter
will explain the benefi t of using fl ow-sharing post-spool compensation,
an advanced style of pressure compensation that will solve this
problem.