What Is The Sealing Pair Of A Lined Ball Valve? What Is The Function Of The Sealing Pair?

The Lined Ball Valve sealing pair consists of a valve seat and a closure member. This refers to the contact between the seat and closure member to achieve closure. The two precision-machined sealing surfaces on the valve seat and closure member maintain a tight seal, or plastically deform under pressure. This seal is crucial for ensuring reliable ball valve operation. Due to wear on the sealing surfaces during the sealing process, sealing performance deteriorates with use.

During use, metal sealing surfaces are susceptible to damage from trapped media and abrasive particles. Valves are also subject to media corrosion, erosion, and cavitation. If the wear particles are larger than the surface roughness, the surface precision of the sealing surface will deteriorate during run-in. Conversely, if the wear particles are smaller than the surface roughness, the precision of the relatively rough surface will improve during run-in. The size of ball valve wear particles depends not only on the material and operating conditions, but also on the lubricity of the media and the potential for contamination and corrosion of the sealing surface. These factors can help reduce the size of the worn sealing surface. Therefore, ball valve seals must be made of materials that are corrosion-resistant, erosion-resistant, and abrasion-resistant. If any of these requirements are not met, the material is unsuitable for the sealing surface. For example, corrosive media can significantly accelerate erosion. Similarly, materials with high corrosion and abrasion resistance are also unsuitable due to their poor abrasion resistance. However, using materials with better performance in ordinary valves is prohibitively expensive, so material selection must consider both application requirements.

There are five types of valve sealing pairs.

1. Plane seal: The two contact surfaces of the sealing pair are flat. This type is easy to manufacture and maintain. When used on globe valves, there is no friction at the moment of closing, but the valve stem is subject to a greater unidirectional force.

2. Cone seal: The two contact surfaces of the sealing pair are conical. This type, when other conditions are the same as those of a plane seal, can achieve higher sealing force and better sealing performance. Cone seals are generally used on high-pressure, small-diameter valves (such as needle valves and plug valves).

3. Spherical seal: One (line contact) or both (surface contact) of the two contact surfaces of the sealing pair are spherical. This type of seal offers excellent sealing performance but is difficult to manufacture and maintain. It is commonly used in ball valves and globe valves.
4. Knife seal: One of the two contact surfaces of the seal is knife-edge shaped. This type of seal is somewhere between linear and flat contact. This type of seal is commonly used in vacuum valves and other applications where the seal is not large.
5. Cylindrical seal.