The pilot piston pressure relief valve is a new type of safety valve which can prevent the dam- age caused by water hammer, but the theoretical research is not yet mature. In this paper, various factors affecting the movement of the pilot piston relief valve are systematically considered, including water pressure, gravity of moving parts, spring force, piston ring friction force and leakage. Based on the principles of structural motion mechanics and hydraulics, the functional relationship between the opening and closing speed of the main valve and the pipeline flow rate of the hydraulic transmission system is obtained, and the mathematical models of the opening and closing speed, stroke and time of the main valve are established. Then, through the analysis of the closing motion equation of the main valve, the existing calculation formula of piston leakage flow is revised, and a method of reasonably selecting the diameter of piston and the diameter, of main valve disc to reduce the influence of water pressure change on the closing process is put forward. Then the calculation formula of main valve closing speed, stroke and closing time are obtained analytically. Finally, the accuracy of the analytical formula is verified by numerical examples, and the effects of some key parameters on the opening and closing of the relief valve are calculated and analyzed. The motion law of the main valve in this paper is also applicable to the piston type pressure fluctuation pre-stop valve. © 2019, China Water Power Press. All right reserved.
