3 – HYDRAULIC PUMPS

This chapter discusses the purpose, operation, and performance of hydraulic pumps. It describes the various methods used to classify pumps and also reviews the types of pumps, such as hydrodynamic, hydrostatic, and rotary pumps, which further include various gear pumps. A hydraulic pump is used to supply the flow of fluid required by a hydraulic system. The pump does not create system pressure; it is created by a combination of the flow generated by the pump and the resistance to flow created by friction and restrictions within the system. As the pump provides flow, it transmits a force to the fluid. When the flow encounters resistance, this force is changed into pressure. A pump must have a continuous supply of fluid available to its inlet port before it can supply fluid to the system. As the pump forces fluid through the outlet port, a partial vacuum or low-pressure area is created at the inlet port. When the pressure at the inlet port of the pump is lower than the atmospheric pressure, the atmospheric pressure acting on the fluid in the reservoir must force the fluid into the pump's inlet. Pumps are normally rated by their volumetric output and discharge pressure. Volumetric output is the amount of fluid a pump can deliver to its outlet port in a certain period of time and at a given speed.