Water hydraulic system using tap water as working fluid is a new driving method which provides high speed, high-output control, while providing safety, hygiene, and ecofriendliness. Its applicable markets widely range from food, health, Pharmaceuticals, cosmetics, semiconductors, beverages, to energy industries. Applications of the water hydraulic technology differ from those of its oil counterpart in heavy industries. This paper is aimed at analytically considering the stability of systems that use tap water as the working fluid. We studied a comprehensive system, including a water hydraulic control valve, a cylinder, and piping for connecting these components, to determine the transfer function of the entire system that has three elements: a control valve; piping and cylinder; and a compensation circuit. Based on the determined function, we reviewed the relationship among natural frequencies of the system, including the control valve and piping, and examined the effect of the control valve and cylinder on the stability of the entire system according to the Hurwitz stability criterion. This gave us a design guideline about the compensation circuit that stabilizes the system by adjusting the natural frequency of the water hydraulic proportional control valve according to the natural frequencies of the piping and cylinder.
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