The pressure gain of hydraulic servovalves is caused by an internal leakage. The leakage flow occurs because of the spool construction and finite radial clearance of th spool. The internal leakage results in unwanted properties such as crawling of a loaded actuator in open loop systems and position error of a P-controlled loaded actuator. On the other hand system damping increases. This paper presents a robust model for internal leakage that can be identified according to known pressure gain. The imporance of the valve's pressure gain on steady state and dynamic behaviour is studied by a well verified simulation model.
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