HYDRAULICS
desired pressure. However, some pressure-compensating pumps have two
valves mounted on the pump body. e two adjustments can look nearly
identical. is type of pressure-compensating pump is called a load-
sensing pump. e second adjustment is called either a "load-sensing"
valve or "fl ow-compensator" valve.
A load-sensing pump is designed to reduce its pressure to a much
lower standby level whenever the system is idle. is can conserve energy
and reduce heat and wear in systems that spend a signifi cant amount of
time in an idle condition. e two separate pressure adjustments allow
setting the compensator valve to the required maximum system pressure
and the load-sensing adjustment to a much lower standby pressure.
Whenever the system is moving a load, the high-pressure adjustment
limits the system pressure. For instance, as a cylinder is extended, pres-
sure in the system will build as necessary to move the load. Eventually,
the cylinder reaches the end of its stroke, and fl ow is blocked. When
the fl ow is blocked in this fashion, the system pressure can build no
higher than the setting of the compensator, but until another load is to
be moved, there is no need for the system pressure to be kept so high.
Most load-sensing systems have a pump-loading directional-con-
trol valve of some sort that can place the system in an idle condition
until it is necessary to move another load. When the pump-loading
valve is shifted, the system pressure drops to the much lower load-
sensing valve setting.
A load-sensing valve usually is smaller than the compensator valve
and typically mounted directly on top of the compensator. e compen-
sator valve is closer to the pump. e load-sensing valve is factory preset
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To System
To System
To System
Pump-loading Valve
Figure 1. A typical confi guration of a
pressure-compensating pump
Figure 2. When system pressure shifts the
load-sensing valve and directs pressure to re-
duce the pump stroke, the pressure drops to the
load-sensing setting of 300 psi.
Figure 3. System pressure shifts the compensator
valve to de-stroke the pump exactly the amount
necessary to limit system pressure to the compensa-
tor setting.
Load-sensing Valve
Load-sensing Valve
Compensator Valve
Compensator Valve
Pump-loading Valve
Pump-loading Valve
Load-sensing Valve
Compensator Valve
