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This paper describes the solution to problems encountered by the valve solution A die-casting machine hydraulic circuit shown in Figure 1, the working process for the pump A exit through a solenoid valve, check valve and pump B The parameters of pump A are rated pressure 6.3 Mpa and rated flow 70 L / min. The parameters of pump B are rated pressure 21 Mpa and rated flow 10 L / min. When the solenoid valve is energized, pump A Total oil supply, the pressure rises to a certain value, the solenoid valve through the pressure relay to power off the pump A unloading, pump B to continue working. Figure 1 Schematic diagram of a hydraulic pressure die-casting machine The circuit in the course of the work of the pump A is often damaged or the impact of the pump life is not long, the phenomenon of the normal reversing valve check, the relief valve can be normal overflow, Other hydraulic parts can work normally. According to the analysis, the pump A is damaged and the pressure at the outlet of the pump A exceeds the maximum pressure of the pump. When the solenoid valve is not energized, pump A is unloaded, and pump A outlet pressure is lowest. When the solenoid valve is energized, the pump oil outlet is connected to the main oil circuit. Due to the relief valve and pressure relay, the pressure here can not rise too high, so the problem is most likely to occur during commutation. Electromagnetic reversing valve in the process of commutation there is a transition process, that is, from left to right bit commutation process P, A, B, T port there is a different on-off relationship, check the transition function of the valve As shown in Figure 2. During commutation, the outlet of pump A is momentarily closed by an instantaneous closing pressure and the pump is damaged by the impact. Figure 2 original electromagnetic reversing valve function symbol After the above analysis and access to domestic and foreign products of the solenoid valve, the die-casting machine put on the transition function shown in Figure 3, the reversing valve. Figure 3 Replacement of the electromagnetic valve function symbol that the pump outlet is still in the commutation process and T cavity connected through this transformation, the pump is damaged by the impact of the reduction, but the service life of the pump is not too long, replaced Different manufacturers of the valve, this phenomenon has not eradicated. The author analyzes the pump is a low-pressure high flow, there is throttling from the P cavity to the T cavity during the transition, the flow through the valve is only 3% to 6% of the rated flow of the valve, and the rest of the flow can not overflow, which may cause For example, the 4WE10 electromagnetic reversing valve in Beijing Hydraulic Factory, the solenoid valve is 40-60 ms for the AC commutation time, and 50-70 ms for the DC solenoid valve. Due to valve machining accuracy, spring manufacturing accuracy, electromagnet response accuracy reasons, and the use of oil in the valve viscosity, cleanliness, temperature and other aspects, the commutation time may be longer than the value provided in the manufacturer's sample so that Pump in the commutation process to withstand a long period of high pressure, affecting pump life. According to the above problem-solving experience, the hydraulic circuit made the following changes, the principle shown in Figure 4. Figure 4 The modified hydraulic circuit In this circuit, when the solenoid valve is not energized, the pump A is unloaded and is isolated from the main oil circuit by the check valve so that the main oil circuit is not affected by the unloading of the solenoid valve. When the solenoid valve is energized, the pump A supplies oil to the system. The transition function of the electromagnetic reversing valve is P, A, B and T are all connected, and can pass the full flow of the pump A and the pressure of the electromagnetic reversing valve during commutation It will not rise. Through such a modification, there is no phenomenon that the pump A is damaged by impact, and the service life can reach the normal state.