| Emulsion pump is power resource of hydraulic support system in coal mine fully-mechanized mining equipment. With the rapid development of modern fully-mechanized mining technology, The demand for Liquid supplying quality of emulsion pump station puts forward higher. For pump with high pressure and large flow, pressure control with electromagnetic unloading valve can meet the timeliness and stability of the working face pressure. Therefore, strengthening the research on structure and overall dynamic performance of electromagnetic unloading valve is help to improve stability and reliability of pump pressure control, and there is a practical significance to ensure the normal operation and safety of fully mechanized mining face.The paper analysed that the structure and working principle of electromagnetic unloading valve, then had stress analysis and established the separately dynamic mathematical model of each component. At last, obtained the transfer function block diagram of valve.The paper established the simulation model of electromagnetic unloading valve in AMESim, and maked dynamic process analysis of valve continuous work in electromagnetic control and mechanical control. Through simulation obtained the main factors affecting the dynamic characteristics of unloading valve on electromagnetic control. The results showed the bigger diameter of pilot orifice hole is,the smaller outlet pressure fluctuation range is, valve is opened more frequently, but the diameter of the orifice hole will cause increasing valve port flow overshoot. The main valve cone half angle increases, outlet pressure fluctuation is the smaller, the faster response speed is, and the lower Unloading pressure is, then reducing the half cone angle is help to reduce the flow fluctuation. The smaller main valve seat diameter is, the smaller outlet pressure fluctuation range is, valve is opened more frequently, and the flow fluctuations is smaller, but unloading pressure is increasesd. The smaller control chamber volume is, the smaller the outlet pressure fluctuation is, the faster response speed of the valve is, but it will cause the outlet pressure and flow overshoot. In addition, control chamber volume is too large to make spool oscillate violently, when the main valve is opened.Numerical simulation of unloading valve flow flied was conduct in FLUENT. Firstly, through2d flow field simulation of pilot valve analysis:The maximum pressure drop of fluid flowing has through valve orifice, the maximum speed of area is along the contour surface of ball valve throttle position, vortex is formed in the orifice outlet and valve cavity outlet oblique flow, this prones to have cavitation damage in the actual work, the spool is impacted on hydraulic shock. Then through2d flow field simulation of the main valve analysis:Simulation results showed the bigger main spool opening is, negative pressure area is smaller, intensity and scope of vortex reduced, The opening is smaller, the maximum speed area is larger and more concentrated in the throttle,(2)The half cone angle increases, negative pressure areas formate smaller, the minimum negative pressure value becomes greater, velocity and vortex is smaller, and high speed region has the trend to move to orifice exit.(3)Changing spool corner with brounded design, the negative pressure^flow velocity and vortex is obviously decreases than before, the possibility of producing cavitation is reduced greatly. At last through3d flow field simulation of the main valve analysis:Fluid flowing past liquid through hole is the loss of pressure, vortex emerges in the cavity formed by the valve cover and body and near wall of liquid through hole. In addition,Through3d simulation of different entrance velocity and outlet pressure can be obtained the larger velocity,or smaller outlet pressure is, negative pressure area、velocity of liquid、intensity and area of ivortex are larger, the energy loss is relatively more.The research of this paper provides a reference for the improvement of the whole performance of electromagnetic unloading valve, and there is a guiding significance for reliable operation of emulsion pump unloading system. |
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