| Hydraulic support is the key equipment of the synthetical mechanized coal mining, the large flow relief valve is the basic component in the hydraulic support system, which protects the security of the entire hydraulic support. With the increase of supporting height and working resistance of the hydraulic support, the better properties of relief valve are demanded. How to improve the dynamic characteristics and flow of relief valve has become an important problem for the researchers.According to the working principle and structure characteristics of the large flow relief valve which is produced by famous company, the paper established the power bond graph of relief valve working system, and then derived the system state equation. According to the state equation, it also established the simulation model on unloading stage of relief valve by using Matlab/Simulink software. It had the pressure and flow curve of the valve port, and the displacement and velocity curve of the valve disk through simulation. The flow of relief valve is 1508L/min. The opening pressure is 44.38MPa. The closing pressure is 39.31 MPa. The dynamic pressure overshoot of relief valve is 6.51%. The peak time is 10.9 milliseconds. The stable time of pressure is 62～73 milliseconds. The paper also discussed how the structure parameters of relief valve (such as dead zone,setting pressure,spring stifiness,the shape of overflow, etc.) affected the dynamic performance of research system. The overshoot of system could decrease when reducing dead zone, valve disk and spring mass, and increasing setting pressure, area of the overflow hole and spring stiffness. Although the overshoot of system could decrease as the liquid resistance of strainer decreases, the stability of valve will get worse. When the shape of overflow is round, the dynamic characteristics of relief valve is the best .When increasing friction force produced between oring and valve housing, and liquid capacitance of valve disk, the stability of valve will get better.The 3-D geometrical model of relief valve was built by using PROE software, according to its actual structure and parameters as well as feasibility of computational mathematical model. The flow field of valve for the opening of 8.3mm was simulated in Fluent. The Pressure drop occurs mainly in overflow hole .The velocity of overflow hole has a maximum value and its value reaches 290m/s. The large whirlpool occurs mainly in flow area and orthogonal turning point. Under certain valve opening(8.3mm), when the pressure difference is 48MPa, the maximum speed near overflow hole is between 285 and 300m/s, the minimum pressure is between -0.105 and -0.091Mpa; When the pressure difference is 45MPa, the maximum speed near overflow hole is between 276 and 290m/s, the minimum pressure is between -0.08 and -0.07 Mpa. With the increase of the pressure difference, the maximum speed of overflow hole will increase, the minimum pressure will decrease, the possbility of air pocket will increase, the whirlpool and energy loss will also increase. Under certain pressure difference(45MPa), when the valve opening is 7.1mm, the minimum pressure of orthogonal turning point is between -0.0995 and -0.0923Mpa; When the valve opening is 8.3mm, the minimum pressure of orthogonal turning point is between -0.068 and -0.037Mpa. With the increase of the valve opening, the minimum pressure of orthogonal turning point will increase, the possbility of air pocket will decrease, and the whirlpool near the corner of valve housing and energy loss will also decrease.The study has offered the significant reference to the relief valve in optimal design. On the other hand, it also has a certain practical meaning to ensure the reliable work of hydraulic support system and the safe and high-efficiency development for mining production.
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