The structure of the solenoid valve reveals that the reason the control oil does not stop after the coil is de-energized is due to the upper small spool valve failing to reset. This could be caused by an insufficiently strong reset spring for the small spool, or a clogged drain path in the large spool valve, which prevents the control oil from being properly discharged. As a result, oil remains trapped in the large spool valve, leading to a stable condition over time. The oil is only released when the vehicle stops, allowing impurities to settle and potentially block the thin oil drain pipe. A blocked drain line can cause delayed drainage during parking, which affects the performance of the large spool valve. Additionally, weak force in the large spool valve or its return spring may contribute to the issue.
For fault diagnosis and resolution, NDO004 was set to 0, and the system was monitored. No abnormalities were found during the visual inspection of the reset button. An on-site test was conducted by pressing PB02, and after 45 seconds, NSW085 was set to 0, with all operations functioning normally. The DCS sequence control table was reviewed, and no irregularities were detected. Multiple chain experiments confirmed that NDO004 was successfully set to 0, and measurements of the DCS output channel showed no issues.
After setting NDO004 to 0, the solenoid valve still did not de-energize. The relay contacts were checked, and since the resistance was within normal limits, the relay was replaced as a precautionary measure. To verify whether the neutral line was grounded, a megohmmeter was used to test the field and main control cables. Both showed a resistance above 100MΩ, indicating no grounding issues. Once the solenoid valve was de-energized, the control of the oil stopped. The return spring of the small spool was inspected, and it was confirmed that the spool moved smoothly under spring force, indicating the spring was in good condition. The movement of both the large and small spools was tested, and there was no evidence of sticking or malfunction.
Overall, the root cause appears to be related to the hydraulic system’s drainage inefficiency rather than electrical faults. Proper maintenance of the oil drain lines and ensuring adequate spring force in the spool valves are key steps in preventing future issues. Regular inspections and cleaning of the system should be implemented to avoid similar problems in the long run.
Water pumps serve in a wide range of applications such as pumping water from wells, aquarium filtering, pond filtering and aeration, in the car industry for water-cooling and fuel injection, in the energy industry for pumping oil and natural gas or for operating cooling towers.
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Materials: Ductile iron, Grey iron, Aluminum
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