Optimization & Practice of Packing Seal for Ball Valves

In numerous industries such as petrochemicals, coal chemicals, and fine chemicals, ball valves play an extremely crucial role. They are not only the terminal control elements in the process flow but also a vital safeguard for production safety. Particularly when dealing with hazardous media such as toxic, corrosive, flammable, and explosive substances, the sealing performance of ball valves directly affects the safe operation of the entire facility. As a key part of the sealing mechanism for ball valves, the importance of packing seals cannot be overstated. This article will delve into the optimization of packing seals for ball valves, using practical case studies to illustrate how to address packing box leakage issues and ensure the reliable operation of the valves.

Ball valves, as widely used control elements, have their sealing performance directly determining their reliability under complex operating conditions. The packing seal is a critical part of the ball valve sealing mechanism, achieving sealing through the interaction between the packing, the valve stem, and the packing box. In actual production, if the packing seal fails, it can not only lead to media leakage but also cause serious safety accidents. For example, when handling toxic media, a packing seal failure can lead to the leakage of toxic gases, endangering the lives of operators. In flammable and explosive environments, leaked media can cause fires or explosions, resulting in significant economic losses and casualties.

Therefore, ensuring the reliability of the packing seal for ball valves is an essential part of ensuring safe chemical production. By continuously optimizing packing seal technology, the risk of leakage can be effectively reduced, improving the safety and operational efficiency of the facility.

In actual production, packing seal failures for ball valves occur from time to time. Through the analysis of faulty valves on site, it has been found that the main causes of packing box leakage are related to the following factors:

The performance of packing seals largely depends on the compatibility of the packing with the media. If there is a chemical reaction between the packing and the media, or if the media is corrosive to the packing, the sealing performance of the packing will be significantly reduced. For example, polytetrafluoroethylene (PTFE) packing is a commonly used sealing material, known for its excellent corrosion resistance and sealing properties, making it suitable for a variety of media. However, under certain special operating conditions, such as high temperature, high pressure, or strong oxidizing environments, PTFE packing can also be corroded, leading to seal failure.

In practical applications, it is essential to select the appropriate packing based on the nature of the media. For most common media, PTFE packing is a good choice, but in some special cases, other types of packing, such as carbon fiber packing or graphite packing, may be required.

The surface finish of the valve stem has a direct impact on the packing seal performance. If the valve stem surface is rough, the contact area between the packing and the valve stem will be reduced, thereby lowering the sealing performance. In actual production, the surface finish of the valve stem usually needs to meet certain standards to ensure that the packing can form a good seal with the valve stem.

Through the inspection of faulty valves on site, it was found that the surface finish of the valve stem was higher than grade 12 (with a roughness of Ra=0.04), which fully meets the sealing requirements. Therefore, the surface finish of the valve stem is not the cause of packing seal failure.

The surface finish of the packing box inner wall is also crucial for the packing seal performance. If the packing box inner wall is rough, it is difficult for the packing to form a uniform seal layer under the pre-tightening force, leading to leakage. In actual production, the surface finish of the packing box inner wall usually needs to meet certain standards to ensure that the packing can form a good seal with the inner wall of the packing box.

After inspection, the surface finish of the packing box inner wall reached grade 7 (with a roughness of Ra=1.6), which meets the sealing requirements. Therefore, the surface finish of the packing box inner wall is not the cause of packing seal failure.

The sealing specific pressure of packing refers to the average normal pressure acting on a unit sealing surface. The magnitude of the sealing specific pressure is an important factor affecting the packing seal performance. In actual production, the sealing specific pressure of the packing needs to be sufficiently high to ensure that the packing can form a good seal with the valve stem and the inner wall of the packing box.

Through the analysis of faulty valves on site, it was found that insufficient sealing specific pressure of the packing is the main cause of packing seal failure. Although the contact surface finish of the packing with the valve stem and the inner wall of the packing box meets the requirements, the insufficient sealing specific pressure of the packing leads to media leakage.

Through an in-depth analysis of the causes of packing seal failure, we have clarified the direction for optimization. To ensure the reliable operation of ball valves and reduce the risk of packing box leakage, we have proposed a series of targeted optimization solutions. These solutions are not only based on theoretical analysis but also combined with practical on-site operating experience, aiming to fundamentally solve the problem of packing seal failure.

Choosing the appropriate packing based on the nature of the media is key to ensuring the performance of the packing seal. In practical applications, PTFE packing is a commonly used sealing material, known for its excellent corrosion resistance and sealing properties, making it suitable for a variety of media. However, under certain special operating conditions, other types of packing, such as carbon fiber packing or graphite packing, may be required.

In this case, the media is not corrosive to PTFE packing, so the selection of PTFE packing is appropriate.

Increasing the sealing specific pressure of the packing is an effective method to solve the problem of packing seal failure. In actual production, the sealing specific pressure of the packing can be increased by increasing the pre-tightening force of the packing gland or by adjusting the packing structure.

In this case, we adopted a structural adjustment measure for the packing, modifying the original V-shaped packing to a U-shaped packing at the bottom. This structural adjustment can further release the deformation capability of the packing, increasing the radial sealing pressure of the packing. After calculation, the radial sealing force of the adjusted packing is much greater than the internal pressure of the media, while also being much lower than the allowable specific pressure of PTFE packing and the yield strength of the valve body material.

Adding pre-tightening measures with disc springs below the packing gland can effectively ensure the pre-tightening force of the packing, increasing the sealing specific pressure. This measure not only reduces the impact of packing wear or stress relaxation on sealing performance but also reduces the maintenance workload of on-site instrument personnel on the packing position, ensuring the reliability of the packing box seal.

In this case, we added pre-tightening measures with disc springs below the packing gland. After more than a year of operation, the ball valve no longer had the problem of packing box leakage, effectively solving the problem of packing seal failure.

Through the implementation of the above optimization solutions, the packing seal performance of the ball valve has been significantly improved. In practical applications, after more than a year of operation, the ball valve no longer had the problem of packing box leakage, effectively solving the problem of packing seal failure. This optimization solution not only improved the sealing performance of the ball valve but also reduced the maintenance workload of on-site instrument personnel, providing a guarantee for the long-term safe operation of the facility.

The optimization of packing seals for ball valves is a systematic project that requires a comprehensive consideration of multiple factors such as the compatibility of media and packing, the surface finish of the valve stem and the packing box inner wall, and the sealing specific pressure of the packing. By conducting an in-depth analysis and optimization of these factors, the problem of packing seal failure can be effectively solved, improving the sealing performance and reliability of ball valves.

In practical applications, selecting the appropriate packing, increasing the sealing specific pressure of the packing, and adding pre-tightening measures with disc springs are effective methods to solve the problem of packing seal failure. The implementation of these measures not only improves the sealing performance of ball valves but also reduces the maintenance workload of on-site instrument personnel, providing a guarantee for the long-term safe operation of the facility.

In summary, the optimization of packing seals for ball valves is an ongoing process of continuous improvement. With the continuous progress of technology and the accumulation of practical experience, we believe that the sealing performance of ball valve packing will continue to improve, providing a more reliable guarantee for the safe production of the chemical industry.