Variable displacement piston pumps are widely used, and graded variable displacement piston pumps are also used in applications such as ice and snow control, where it may be desirable to change system flow without changing engine speed. This is where the plunger pump comes into play. When hydraulic flow requirements vary according to operating conditions. Unlike fixed displacement designs, the angle of the rotating swash plate is not fixed and can be adjusted by a compensator through pressure signals from the directional valve.

 

If more flow is required, the angle of the rotating swash plate will change, increasing the displacement of the pump by generating longer piston strokes. Unlike fixed displacement piston pumps, quantity is used in closed systems. For a closed system, the angle of the rotating swash plate inside the pump decreases with the decrease of flow requirements, so that there is no excessive loss of flow or hydraulic horsepower. Piston pumps can be flow compensated, pressure compensated, or flow and pressure compensated. Flow compensation adjusts the angle of the rotating swash plate to maintain a constant pressure range as the flow requirements change. Pressure compensation can maintain flow rate by adjusting the angle of the inclined plate regardless of changes in system pressure. These systems with flow and pressure compensation combinations are commonly referred to as load sensing systems, which are common for snow and ice control vehicles.

 

When high operating pressure is required, a pump is usually used. Traditionally, pumps have been subjected to higher pressure than gear pumps with considerable displacement; However, the initial cost associated with piston pumps is high, and the pollution is low and the complexity increases. This complexity is understood by equipment designers and maintenance personnel, as piston pumps operate normally with additional moving parts, strict filtration requirements, and strict tolerances. Piston pumps are typically used with vehicle mounted cranes, but can also be found in other applications such as ice and snow control, which may require changing system flow without altering engine speed.

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