Problems with the diverter valve
This paper presents a detailed analysis and solution to the issues encountered in the hydraulic circuit of a die-casting machine, as illustrated in Figure 1. The system involves two pumps—pump A and pump B—connected through a solenoid valve and a check valve. Pump A has a rated pressure of 6.3 MPa and a flow rate of 70 L/min, while pump B operates at a higher pressure of 21 MPa with a flow rate of 10 L/min. During operation, when the solenoid valve is energized, pump A supplies oil to the main circuit. As the pressure rises, the pressure relay triggers the solenoid valve to de-energize, allowing pump A to unload, while pump B continues to operate.
However, during normal operation, pump A often experiences damage or shortened lifespan due to excessive pressure spikes. While the relief valve functions properly and other components work normally, the issue primarily occurs during the switching process of the solenoid valve. When the electromagnetic reversing valve switches, there is a transitional phase where the P, A, B, and T ports experience different on-off states. This transition can cause a momentary closure of the pump A’s outlet, leading to pressure surges that damage the pump.
After analyzing the original valve function symbol (Figure 2), it was found that the pump A's outlet remained connected to the T cavity during the transition, increasing the risk of damage. To address this, an improved electromagnetic reversing valve with a modified function symbol (Figure 3) was installed. Although this reduced the impact on the pump, the service life was still not satisfactory, as the problem persisted across different manufacturers.
Further investigation revealed that pump A is a low-pressure, high-flow unit, and during the transition, only 3% to 6% of the rated flow passes through the valve, while the rest is blocked. This leads to pressure buildup, especially with valves like the 4WE10 from Beijing Hydraulic Factory, which have AC commutation times of 40–60 ms and DC times of 50–70 ms. However, factors such as machining tolerances, spring quality, electromagnet response, and oil viscosity can extend the actual commutation time, causing prolonged high-pressure exposure and reducing pump life.
Based on these findings, the hydraulic circuit was redesigned (as shown in Figure 4). In the new configuration, when the solenoid valve is not energized, pump A is unloaded and isolated from the main circuit by a check valve, preventing unnecessary pressure fluctuations. When the solenoid valve is activated, pump A supplies oil to the system, and the electromagnetic reversing valve allows full flow without pressure rise during the transition. This modification successfully eliminates the issue of pump A being damaged by pressure surges, significantly extending its service life and restoring normal system performance.
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