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In the hydraulic system of agricultural machinery, pressure valves are widely used components. A sudden failure of a pressure valve can severely disrupt the normal operation of the equipment, leading to downtime and potential damage. This article explores the common causes of pressure valve failures and introduces practical testing methods through examples.
First, let's examine the typical reasons for pressure valve malfunction:
1. **Wear and Tear**: Over time, the hydraulic spool and valve body experience constant friction, which can alter their dimensions, shape, and surface quality. This wear reduces the precision and efficiency of the valve.
2. **Fatigue and Cracks**: The balance spring, valve core, and valve seat operate under fluctuating loads, leading to material fatigue. This can result in cracks, broken springs, or flaking on the sealing surfaces.
3. **Material Deformation**: Residual stresses from manufacturing processes and external loads during use may exceed the yield strength of the materials, causing deformation of the valve parts.
4. **Corrosion from Contaminants**: If the hydraulic oil contains excessive water or acidic substances, prolonged exposure can corrode internal components, reducing accuracy and performance.
5. **Radial Force Imbalance**: Uneven radial forces between the valve core and sleeve can cause the valve core to jam against the inner wall of the valve sleeve, leading to operational issues.
6. **Poor Manufacturing or Maintenance**: If the valve is not manufactured or repaired according to technical specifications, or if parts become rusted or contaminated, it can lead to premature failure.
Next, we'll look at some common test methods for pressure valves, using a pressure relief valve as an example.
**Testing Methods:**
1. **Pressure Regulation Range and Stability Test**: Adjust the valve’s adjustment knob from fully open to fully closed and back again. Monitor the pressure gauge to observe the pressure changes. The pointer should move smoothly, and the pressure range must meet the specified limits, with pressure fluctuations within acceptable levels.
2. **Leakage Test**: Set the valve to the fully closed position and adjust the overflow relief valve to the maximum pressure. Then, measure the leakage by adjusting the test valve until the overflow is detected.
3. **Unloading Pressure Test**: Connect the remote control port of the relief valve to the tank. Pass the test flow through the valve and measure the inlet and outlet pressures. The difference represents the unloading pressure.
4. **Pressure Loss Test**: Loosen the valve adjustment completely and allow full flow through the valve. Measure the pressure drop between the inlet and outlet to determine the pressure loss.
5. **Opening and Closing Characteristics**: Close the overflow relief valve and set the tested valve to its maximum pressure. Gradually reduce the system pressure and measure the overflow volume when the valve closes. Then, gradually increase the pressure until the valve opens and record the opening pressure.
These tests help ensure the reliability and performance of pressure valves, which is crucial for the efficient and safe operation of agricultural machinery. Regular maintenance and proper testing can significantly extend the service life of these critical components.
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