Analysis Of Releasing Curve And Valve For High Pressure Chamber

The working pressure of large hydraulic press is very high, the system will maintain high oil pressure at some stage of the operation. Due to compression,the oil in high pressure chamber composed of main working cylinder and part hydraulic lines will reach the maximum pressure in the holding stage. After the holding stage, it needed to release the compressed oil inside the chamber before enter the rapid return stage, this procedure called pressure relief process. In order to ensure the stability and rapidity of the hydraulic press, the pressure relief process must be controlled reasonably. Fast pressure relief rate will form huge hydraulic impact, causing the system vibration, and affect the stability of hydraulic press; Slow pressure relief rate will extend the operation period of equipment, reduce the production efficiency, and affect the rapidity of the hydraulic press. Therefore, in order to take into account the needs of hydraulic stability and rapidity, a thorough and comprehensive study on the rule of pressure relief is necessary.In this paper, the commonly used pressure relief circuit of the hydraulic press is analyzed. To ensure the stability of the pressure relief process, most of them through the method of time prolonging, ignored the demand for rapid. The application of electro-hydraulic proportional valve can control the pressure relief process effectively, but the research on the pressure relief law is not thorough enough,which makes it difficult to determine the open curve. At the same time,the cost of the valve is higher and the use environment is strict. The existing methods of pressure relief are not perfect, only study from the mechanism of pressure relief impact can get a more reasonable pressure relief law to guide the process of pressure relief.The root reason of the pressure relief impact, the sudden and irregular change of oil momentum, is pointed out through the analysis of the mechanism. The maximum rate of momentum change is obtained by the formula derived and calculated, and a pressure relief law by control the oil momentum change according to the maximum rate of momentum change is proposed. The pressure relief process is calculated by selecting the parameters of a certain type of hydraulic press,and obtained the change laws between chamber pressure, valve core opening area, oil flow rate and time.If the valve core opening area changs with the chambe pressure according to the law, the pressure relief process can be carried out quickly and smoothly.Based on the analysis and calculation of pressure relief law, a new special pressure relief valve is designed. This valve uses a variable orifice, can control the movement of the valve core directly by the chamber pressure to change the orifice area in real time.And it can make the pressure relief process accroding to the law, achieved fast pressure relief without impact. Compared with electro-hydraulic proportional valve, it has the advantages of simple structure, low cost, easy to use, easy to determine the open curve and stronger applicability. At the same time, the pressure relief is designed, and it’s composition and working principle are introduced.The new pressure relief valve model and circuit were established through the AMESim software. Simulation analysis results show that the ressure relief process can be carried out quickly and smoothly,and the the spool can quickly respond when pressure changes. The rationality of pressure relief law and the design feasibility of pressure relief valve were verified by comparing the simulation curve with the theoretical curve.Besides, the pressure relief time influence factors are analyzed,and some suggestions are proposed on how to shorten the time of pressure relief process.