The main control valve is a key part of mobile hydraulic control systems. The main control valve consists of several types of spool valves. A notch is usually introduced to the end of the spool valve to reduce the influence of the flow force generated by the movement of fluid. In this study the flowrate from a spool valve combined with a servo-valve system is controlled based on an accurate prediction of transient pressure-flow relations by CFD. The transient analyses inside the spool valves with three typical types of notch are performed using a commercial CFD code of Fluent™. The flow characteristics such as flow pattern, discharge coefficient, and flow force, which depend on the notch shapes and their openings, are analyzed via vorticity distributions. Hysteresis of flow coefficients is observed for opening and closing motions of the spool valve, which should be compensated by the servo-valve in order to control the designed rate change of flowrate.

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