What is the leakproof structure of stainless steel ball valves?

With its well-known advantages, the stainless steel ball valves are widely used in the control of various pipeline systems, which can be used in change of flow direction and automatic control of the system. In the application of the stainless steel ball valves, its control can be driven manually, electrically or pneumatically.

In the performance of the stainless steel ball valve, the tightness of sealing is one of its main indicators. It can be seen that the sealing structure of the ball valve is mainly composed of three parts. One is the sealing between the main and auxiliary valve bodies, which is realized by the sealing gasket. The second is the sealing between the main valve body and the stem, which is based on the seal rings to form the sealing structure of the valve outside. The third is the sealing between the body and the main and auxiliary valve bodies, which is realized by the seal block to form the main structure for sealing of the stainless steel ball valve. The tightness of the main structure for sealing affects the working performance of the stainless steel ball valve, and it is the key structure in the design and manufacture of the ball valve.

Sealing Requirements

The sealing index of the stainless steel ball valve is determined by the requirements of internal and external leakage. National standards stipulate that the tightness of the stainless steel ball valves is that there should be no visible leakage within the duration of the test in accordance with "General Valve Pressure Test" .

Analysis of Main Structure for Sealing

The stainless steel ball valves in early time generally used metal to make the sealing structures. With the development of engineering plastics, especially the emergence of polytetrafluoroethylene, the sealing structure of the ball valve have an ideal material.

The soft sealing of the sealing structure of the stainless steel ball valves includes seal blocks with elastic elements, seal blocks with polytetrafluoroethylene rings and combined seal blocks composed of elastic rings and so on. The lip-type seal block has a lip-shaped structure, which makes it have good elasticity. In use, it can ensure and compensate the pre-compression of the sealing surface, which is better than the rigid structure.

However, during use, it was found that the ability in elastoplastic deformation of PTFE and the stability under changes of temperature are still not ideal. At the same time, because the wide range of operating pressure of the stainless steel ball valve, the lip-type seal made of polytetrafluoroethylene is still prone to cause leakage under low pressure or in long-term use.

Finally, the way to solve this problem is to use a combined seal composed of an elastic ring for expansion and a lip-type seal made of  polytetrafluoroethylene. It can rely on the good ability in elastoplastic deformation of the metal material to enhance its overall ability in elastoplastic deformation and compensation ability to improve the sealing ability of the stainless steel ball valve.