A novel pilot stage valve called simplified 2D valve, which utilizes both rotary and linear motions of a single spool, is presented. The rotary motion of the spool incorporating hydraulic resistance bridge, formed by a damper groove and a crescent overlap opening, is utilized as pilot to actuate linear motion of the spool. A criterion for stability is derived from the linear analysis of the valve. Special experiments are designed to acquire the mechanical stiffness, the pilot leakage and the step response. It is shown that the sectional size of the spiral groove affects the dynamic response and the stiffness contradictorily and is also very sensitive to the pilot leakage. Therefore, it is necessary to establish a balance between the static and dynamic characteristics in deciding the structural parameters. Nevertheless, it is possible to sustain the dynamic response at a fairly high level, while keeping the leakage of the pilot stage at an acceptable level.
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