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, specifically focusing on the valve system shown in Figure 1. The system involves two pumps: Pump A with a rated pressure of 6.3 MPa and a flow rate of 70 L/min, and Pump B with a higher pressure rating of 21 MPa and a lower flow rate of 10 L/min. The operation of the system relies on a solenoid valve, check valve, and pressure relay to control the flow and pressure within the circuit. When the solenoid valve is energized, Pump A supplies oil to the main circuit, causing the pressure to rise. Once the pressure reaches a set threshold, the pressure relay de-energizes Pump A, allowing it to unload while Pump B continues to operate. However, during this switching process, Pump A often experiences damage or reduced service life due to high-pressure shocks. Through detailed analysis, it was determined that the outlet pressure of Pump A exceeds its maximum allowable pressure, especially during the transition phase when the solenoid valve switches. This occurs because, during the commutation of the electromagnetic reversing valve, there is a brief moment where the pump’s outlet is momentarily closed, leading to a sudden pressure spike that damages the pump. The original electromagnetic reversing valve (as shown in Figure 2) has a transition function where the P, A, B, and T ports are not fully connected during the switch, resulting in restricted flow and pressure buildup. After evaluating domestic and international solenoid valve options, a modified valve with improved transition characteristics was implemented (Figure 3). Although this change reduced the impact on Pump A, the issue was not completely resolved, as different manufacturers' valves still exhibited similar behavior. Further investigation revealed that Pump A, being a low-pressure, high-flow pump, experiences throttling during the transition phase. Only 3% to 6% of the valve's rated flow passes through the valve, while the rest cannot be effectively diverted, leading to pressure surges. Additionally, factors such as valve manufacturing tolerances, spring quality, electromagnetic response time, and oil viscosity can extend the commutation time beyond the manufacturer's specifications, increasing the risk of damage. Based on these findings, modifications were made to the hydraulic circuit (as illustrated in Figure 4). In the new design, when the solenoid valve is not energized, Pump A is isolated from the main circuit via a check valve, preventing unnecessary unloading. When the solenoid valve is activated, Pump A supplies oil to the system, and the electromagnetic reversing valve ensures full flow passage without pressure buildup during switching. These changes successfully eliminated the issue of Pump A being damaged by pressure shocks, significantly extending its service life and restoring normal system performance.

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