Hydraulic Variable Displacement Pump

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Hydraulic open loop system
Hydraulic open loop system

An expensive hydraulic variable displacement pump offers many options for hydraulic circuit design. The pump displacement can be changed using a servo valve to manipulate the actuator speed movement. The open loop hydraulic design as shown in figure above can be re-design in to a closed loop system by adding sensor on the gearbox output shaft. The sensor output voltage is compared to the setting point which is representing the speed setting. The voltage difference between the setting point and the actual speed is used to increase or decrease the pump displacement. The error voltage signal is used to move the servo valve spool by rotating the torque motor. The hydraulic oil is directed to the control pistons to extend or retract and change the angle of the swash plate. The manipulation of the swash plate changes the pump displacement.

A servo pump is a variable displacement pump with a servo valve mounted on the pump. This pump combination doesn’t need any pressure drop to control the actuator speed, thus this system is more efficient to control actuator speed.

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