The main seat sealing ring material of all manual ball valves is polytetrafluoroethylene (PTFE), which is inert to almost all chemical substances, and has the comprehensive characteristics of small friction coefficient, stable performance, easy aging, wide temperature application range and excellent sealing performance. However, the physical properties of teflon, including high coefficient of expansion, sensitivity to cold flow and poor thermal conductivity, require that the valve seat seal be designed around these characteristics. Plastic materials for seat sealing also include filled teflon, nylon and many other materials. However, when the sealing material becomes hard, the reliability of the seal will be damaged, especially in the case of low pressure difference. In addition, synthetic rubber such as butadiene rubber can also be used as a seat sealing material, but it is suitable for the medium and the temperature range used is limited. In addition, if the medium is not lubricated, the use of synthetic rubber is easy to jam the sphere. In order to meet the requirements of high temperature, high pressure, strong erosion, long life and other industrial applications, the metal sealed ball valve has been greatly developed in the past ten years. Especially in industrially developed countries, such as the United States, Italy, Germany, Spain, the Netherlands, etc., the structure of the ball valve continues to improve, the emergence of fully welded valve body directly buried ball valve, lifting ball valve, so that the ball valve is more and more widely used in industrial fields such as long-distance pipelines and refining units. Ball valves with large diameter (3050mm), high pressure (70MPa) and wide temperature range (-196 ~ 815 degrees) have appeared, so that the technology of ball valves has reached a new level.