Variable Displacement Pump Leakage Characteristics

If the pump is driven at constant speed, the flow from the pump is directly proportional to the pump stroke. The output pressure or discharge pressure from the pump is determined by the load or the restriction to the pump discharge flow. As the pressure is increased, the discharge flow will decrease because of leakage from the high-pressure passageways of the pump. This leakage takes place through the clearances between the pistons and the cylinders and between the pintle and cylinder block.

Since the leakage paths of a pump tend to be long, the leakage as a function of pressure win approach a constant. However, with very low viscosity fluids over a large range of pressures, the leakage characteristics will become increasingly more nonlinear.

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