Detection and Treatment of Internal Leakage in Plug Valves

Plug valves are essential components in fluid control systems, widely used in industries such as oil, chemicals, and water supply. Internal leakage can not only reduce system performance but also pose safety risks. Therefore, timely and effective detection and treatment of internal leakage in plug valves are crucial for ensuring the safety and reliability of the system. Below is a detailed guide on how to identify and address internal leakage in plug valves.

Identifying Internal Leakage

The detection of internal leakage in plug valves primarily relies on temperature changes on the valve surface and sound detection. Based on different detection results, internal leakage can be categorized into three types.

1. No Leakage

If you touch the valve body and the downstream pipeline and feel no coldness, it indicates that no fluid is leaking. Generally, the absence of temperature change suggests that fluid is not flowing inside the valve. If the valve body and downstream pipeline are dry and clean, it indicates no internal leakage. Listening closely to the pipe wall and hearing no sound of escaping fluid confirms that the valve is in normal condition, demonstrating good sealing performance.

2. Slight Leakage

If the valve body and downstream pipeline feel slightly cold, it may indicate minor leakage. This temperature change typically correlates with the leakage level; as leakage increases, the temperature difference becomes more pronounced. You might see no obvious water droplets on the valve body or downstream pipeline, but there may be minor moisture present. Watch for any increasing trend in water droplets, which could signal worsening leakage. If you listen closely to the pipe wall, you might hear faint sounds of escaping fluid, indicating slight leakage. In this case, further inspection and maintenance should be carried out promptly to prevent worsening of the issue.

3. Severe Leakage

If the valve body and downstream pipeline feel distinctly cold, it suggests significant fluid leakage. This cold sensation is usually caused by a large flow of fluid leaking, leading to a noticeable drop in surface temperature. The presence of water droplets on the valve body and downstream pipeline (which may freeze in winter) is a clear sign of severe internal leakage, indicating continuous fluid leakage and condensation on the surface. You can hear the sound of escaping fluid without putting your ear directly against the pipe wall, which shows that the leakage is serious. This sound often comes from fluid passing through the valve that has not fully closed, and it needs urgent attention.

Treatment with Grease Injection

For newly detected or slightly leaking plug valves, grease injection is a common and effective solution. The specific steps are as follows.

1. Choose Injection Points

Full Closure Injection: Inject grease when the valve is completely closed to ensure no fluid is passing through the valve. This position maximizes the sealing effect, ensuring that the new grease fills the sealing cavity completely.
Multi-Position Injection: Depending on the severity of the leakage, inject grease at fully open, mid-position, and fully closed positions to ensure an even distribution of sealing grease for optimal results. This method helps maintain good sealing performance under different operating conditions.

2. Handling Slightly Severe Leakage

Using a Cleaning Agent: For slightly severe leakage, it is advisable to inject a cleaning agent into the valve and let it soak for 24 hours before injecting grease. The cleaning agent effectively softens and dilutes old grease, clearing the injection passages inside the valve and reducing potential blockages.
Effect of Sealing Grease: After injecting new grease, it can push out the old grease, restoring the sealing effect and ensuring the valve functions normally. This method is suitable for cases where sealing grease has aged and failed due to long-term use.

3. Bottom Adjustment

Adjusting Screws: If grease injection is ineffective, it may be due to excessive wear causing increased clearance between the plug and the valve body. In this case, you can gently tighten the bottom adjustment screws to readjust the clearance between the plug and the valve body, followed by grease injection. It is important to ensure the clearance is appropriate to avoid impacting valve operation.

Care must be taken when adjusting the screws, as overtightening may prevent the valve from opening properly, affecting its use. Operators should have experience and sensitivity to find the right amount of force during adjustments.

Disassembly and Repair

If the above methods do not resolve the leakage issue, consider disassembly and repair. The steps include the following aspects.

1. Disassembling the Valve

Take apart the plug valve, remove the plug, and thoroughly clean the plug cavity to remove aged and hardened sealing grease. Also, check for noticeable scratches on the plug surface and repair them through grinding. This step is crucial for restoring the sealing performance of the valve, ensuring it can function as intended.

2. Reinstallation

When reinstalling the plug, if any surface defects are found, rotate the plug 180° during installation to swap the pressurized and non-pressurized surfaces, optimizing the sealing effect. This method helps avoid using the same worn areas, thereby improving the reliability of the sealing effect.

3. Injecting New Sealing Grease

After reassembly, inject new sealing grease to ensure an effective seal between the plug and the valve body, restoring the valve's functionality. The injection of new grease effectively fills all gaps, providing good sealing properties.

Analyzing Repair Effectiveness

While disassembly and repair can remove old, degraded sealing grease and restore grease injection passages, the overall effectiveness may not meet expectations. Here are some common reasons for subpar repair results.

1. Limitations of Sealing Performance Recovery

For internal leakage caused only by hardened old grease, removing it and injecting new grease can restore sealing performance. However, if there is wear, scratches, or deformation between the plug and the valve body, this method won't solve the problem. This means that unless wear issues are thoroughly addressed, merely injecting grease may not maintain sealing effectiveness over time.

2. Difficulty in Restoring Clearance

The plug and valve body are precision machined and paired with adjusted clearances at the factory. After disassembly, it is hard to recreate the original clearance, which can affect sealing effectiveness. Even if adjustments are made during the repair, it may be impossible to restore the original precision, leading to continued weakening of the sealing effect.

Conclusion

Timely detection and treatment of internal leakage in plug valves can effectively extend their lifespan and ensure the safe operation of the system. Users should flexibly apply grease injection and disassembly repair methods based on the leakage situation to keep the valves performing at their best. Regular maintenance and monitoring of valve conditions will help reduce the likelihood of internal leakage and enhance the overall reliability of the system. By implementing proper operation and maintenance, the functionality of plug valves can be maximized, ensuring the stability and efficiency of fluid control systems.