Although the use of water is neither new nor innovative, the use of water as a working fluid in hydraulic circuits is receiving an increasing attention by both manufactures and users due to its fire resistance and environmental compatibility. The water hydraulic components are being developed thoroughly. Materials, machining technology, structures and so on must be examined for whether or not they are compatible with water when the components are designed. The purposed of this paper is to show a water hydraulic unloading relief valve and its principle which is invented by Zhejiang university. From the view of flow control, the method of cavitation resistance of a water hydraulic unloading relief valve are investigated. The computational fluid dynamics approaches are applied to obtain static pressure distributions and cavitation images in the channel of the main stage of the valve with four kinds of structure. These structure consist of one-stage throttle, one-stage with high-pressure induct, two-stage throttle and two-stage throttle with high-pressure induct. The experiments are carried out with different supply pressure, flow rate and the opening on the pilot-operated water hydraulic relief valve. The results show that the method of combined cascading restrictors with high-pressure induct can effectively restrain cavitaion.
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