VARIABLE-DELIVERY PISTON PUMPS
A variable-delivery piston pump automatically and instantly varies the amount of fluid delivered to the
pressure circuit of a hydraulic system to meet varying system demands. This is accomplished by using a
compensator, which is an integral part of the pump. The compensator is sensitive to the amount of
pressure present in the pump and in the hydraulic system pressure circuit. When the circuit pressure
rises, the compensator causes the pump output to decrease.
Conversely, when circuit pressure drops, the compensator causes pump output to increase. There are
two ways of varying output--demand principle (cam) and stroke-reduction principle (angular).
Demand Principle. The demand principle (Figure 1-8) is based on varying pump output to fill the
system's changing demands by making the piston stroke effective in varying degrees.
Figure 1-8. Variable-Delivery Demand-Principle Cam Pump.