Objective The reversing valve failures in metro train brake system's twin-tower dryer may prevent the dryer from switching between drying and regeneration states, and further triggering the shutdown of air compressors. Therefore, it is necessary to analyze the root cause of the reversing valve failure and develop targeted preventive measures.

Method Taking multiple failures of twin-tower dryers on Hefei Metro Line 5 as examples, the reversing valve is confirmed as the failure point by combining the fault logic and the working principle of twin-tower dryers. Through disassembling failed reversing valves, piston component dimension measurements, actuation force tests, and failure simulations are conducted. The causes of the reversing valve failure are analyzed in depth from the piston component dimension, valve cover installation torque, and dust seal inner diameter three aspects.

Result & Conclusion  The test results indicate that the piston component dimensions all meet the design requirements, and the valve cover installation torque has no significant impact on the piston action. However, the inner diameter of the dust ring directly affects the smoothness of the piston assembly movement. The root cause of the reversing valve failure is finally determined to be that the inner diameter dimensions of the dust ring and the piston guide reaching the lower limit of the design requirements. Subsequently, a special inspection has been carried out on all trains of Hefei Rail Transit Line 5, and preventive replacement of abnormal components has been implemented.