This paper studies the use of modified pneumatic on/off spool valve as a proportional valve in low-pressure water hydraulics. The most inexpensive solution is to use the modified pneumatic valve without spool position feedback but the characteristics are not good enough for most cases. The characteristics of the valve with spool position feedback and Pi-controller are introduced and compared to the characteristics of a reference valve. The reference valve is a water hydraulic proportional valve with hydrostatic bearings on both ends of the spool. The characteristics of the reference valve in low-pressure water hydraulics are good although the valve is designed for high-pressure water hydraulics. The results show that with spool position feedback and Pi-controller the characteristics of the modified pneumatic valve are quite good when used at low pressure levels.
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