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.

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.

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.

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.

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

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

The difference between the two inner diameters is generally twice the thickness of the gasket to ensure that after compression, the inner edge of the gasket does not protrude into the container or pipeline, so as not to hinder the flow of fluid in the container or pipeline. The pre-tightening force of the gasket should not exceed the design specifications to avoid excessive compression and loss of rebound ability of the gasket. When tightening the gasket, it is best to use a torque wrench.

For large bolts and high-strength bolts, it is best to use hydraulic tighteners. The tightening torque should be calculated based on the given gasket compression, and the magnitude of the hydraulic tensioner oil pressure should also be determined through calculation.

When installing the gasket, tighten the nuts in the order shown in the diagram on the right. But it should not be twisted once to reach the design value. Generally, it should be cycled at least two to three times to ensure even distribution of gasket stress. For pressure vessels and pipelines with flammable and explosive media, safety should be used when replacing gaskets.

All tools are used to avoid sparks caused by collisions between tools and flanges or bolts, which may lead to fire or explosion accidents. If there is a leak in the pipeline, it must be depressurized before replacing or adjusting the installation gasket. It is strictly prohibited to operate under pressure.

Special requirements for gasket installation

When installing the spiral gasket that matches the protruding flange, attention should be paid to ensuring that the seal is concentric with the pipeline. Generally, an external strong ring is used to contact the inner circumferential surface of the bolt for positioning, and eccentric installation is not allowed.

When installing the basic spiral wound gasket in the sealing surface flange of the mortise and tenon groove, attention should be paid to keeping the gap consistent with the groove wall surface.

When installing metal coated gaskets with narrow widths, a certain thickness of steel plate should be placed on the outside of the gasket, and then the flange should be tightened to prevent the filling material inside the gasket from being compressed and causing the interface (or lap joint) of the metal shell to expand and damage the gasket.

When the working temperature of the flange is higher than 200 ?, sealant should be applied between the flange sealing surface and the gasket to prevent the gasket from sintering with the flange sealing surface under high temperature, which will increase the trouble of maintenance and gasket replacement.

If the sealing surface is irregular, apply sealant on the sealing surface before installing the gasket. Sealing glue is generally composed of manganese dioxide, graphite powder, and boiled linseed oil (dry oil).? The corresponding type and grade of liquid sealant can be selected according to the sealing medium, working temperature, and medium pressure conditions.

For the installation of octagonal metal ring gaskets, when the machining of the metal ring gasket and flange sealing groove is not ideal, a tight fit can be achieved through mating. For large diameter metal ring pads, it is difficult to match and research them. In order to fill the small unevenness on the metal surface, sealant can be used.

Notes for gasket installation

The sealing surface ofgasketsand flanges should be cleaned thoroughly, and there should be no defects such as scratches or spots that affect the sealing performance of the connection.? The outer diameter of thegasketshould be smaller than that of the flange sealing surface, and the inner diameter of the gasket should be slightly larger than the inner diameter of the pipeline.

The difference between the two inner diameters is generally twice the thickness of the gasket to ensure that after compression, the inner edge of the gasket does not protrude into the container or pipeline, so as not to hinder the flow of fluid in the container or pipeline. The pre-tightening force of the gasket should not exceed the design specifications to avoid excessive compression and loss of rebound ability of the gasket. When tightening the gasket, it is best to use a torque wrench.

For large bolts and high-strength bolts, it is best to use hydraulic tighteners. The tightening torque should be calculated based on the given gasket compression, and the magnitude of the hydraulic tensioner oil pressure should also be determined through calculation.

When installing the gasket, tighten the nuts in the order shown in the diagram on the right. But it should not be twisted once to reach the design value. Generally, it should be cycled at least two to three times to ensure even distribution of gasket stress. For pressure vessels and pipelines with flammable and explosive media, safety should be used when replacing gaskets.

All tools are used to avoid sparks caused by collisions between tools and flanges or bolts, which may lead to fire or explosion accidents. If there is a leak in the pipeline, it must be depressurized before replacing or adjusting the installation gasket. It is strictly prohibited to operate under pressure.

Special requirements for gasket installation

When installing the spiral gasket that matches the protruding flange, attention should be paid to ensuring that the seal is concentric with the pipeline. Generally, an external strong ring is used to contact the inner circumferential surface of the bolt for positioning, and eccentric installation is not allowed.

When installing the basic spiral wound gasket in the sealing surface flange of the mortise and tenon groove, attention should be paid to keeping the gap consistent with the groove wall surface.

When installing metal coated gaskets with narrow widths, a certain thickness of steel plate should be placed on the outside of the gasket, and then the flange should be tightened to prevent the filling material inside the gasket from being compressed and causing the interface (or lap joint) of the metal shell to expand and damage the gasket.

When the working temperature of the flange is higher than 200 ?, sealant should be applied between the flange sealing surface and the gasket to prevent the gasket from sintering with the flange sealing surface under high temperature, which will increase the trouble of maintenance and gasket replacement.

If the sealing surface is irregular, apply sealant on the sealing surface before installing the gasket. Sealing glue is generally composed of manganese dioxide, graphite powder, and boiled linseed oil (dry oil).? The corresponding type and grade of liquid sealant can be selected according to the sealing medium, working temperature, and medium pressure conditions.

For the installation of octagonal metal ring gaskets, when the machining of the metal ring gasket and flange sealing groove is not ideal, a tight fit can be achieved through mating. For large diameter metal ring pads, it is difficult to match and research them. In order to fill the small unevenness on the metal surface, sealant can be used.