In hydraulic circuits, the pump is the device that creates the flow of hydraulic fluid. The pump converts energy supplied to it from a motor or engine into rotational force. Hydraulic pumps are either positive displacement pumps or variable displacement pumps. Displacement refers to the flow of fluid through the pump per rotation. In a positive displacement pump, the flow rate cant be changed. In contrast, the flow rate in a variable displacement pump can be changed. This change allows for the saving of power and energy which otherwise would be lost doing normal changes in work loads. Different types of pumps include gear, vane, piston, rotary vane, and bent axis pumps. Bent axis pumps are the most efficient pumps, however, the gear pumps are the simplest and cheapest type.
Flow rate of the pump is proportionally related to the actuator speed; the actuator speed depends on the flow rate of the pump, faster pump faster output. Most pumps are used in an open system, which means the reservoir is not pressurized. If the reservoir is pressurized then it’s a closed system. Examples of machines that couldn't operate without the use of hydraulic pumps are cranes, loaders, backhoes. Power steering in cars also use hydraulic pumps.
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