4. Sealing of pneumatic ball valve The most important material for sealing ring of valve seat of pneumatic ball valve is polytetrafluoroethylene (PTFE), which is inert to almost all chemicals, and has comprehensive characteristics of small friction coefficient, stable performance, aging resistance, wide temperature application range and excellent sealing performance. However, the physical characteristics of PTFE, including high expansion coefficient, sensitivity to cold flow and poor thermal conductivity, require that the design of valve seat seal must focus on these characteristics. Plastic materials for seat sealing also include filled PTFE, 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 valve seat sealing material, but its applicable medium and temperature range medicine are limited. In addition, if the medium is not lubricated, it is easy to jam the ball with synthetic rubber. In order to meet the requirements of industrial applications such as high temperature, high pressure, strong erosion and long life, metal sealed pneumatic ball valves have been greatly developed in the past decade. Especially in countries with developed industries, such as the United States, Italy, Germany, Spain, the Netherlands, etc., the structure of pneumatic ball valves has been constantly improved, with the emergence of all welded body directly buried pneumatic ball valves, lifting pneumatic ball valves, which has made pneumatic ball valves more and more widely used in long-distance pipelines, oil refining units and other industrial fields, with large diameter (3050mm), high pressure (70MPa) The pneumatic ball valve with a wide temperature range (- 196~815 ℃) enables the technology of the pneumatic ball valve to reach a new level.

Next, let's make a detailed explanation for you. The application environment of pneumatic butterfly valve needs to consider the following five elements:
1. Temperature
The rated working pressure of the pneumatic butterfly valve used at high temperature must be reduced according to the temperature correction coefficient of the working pressure of the pneumatic butterfly valve at high temperature, so as to ensure that the valve is stopped under safe conditions.
2. Corrosion
The pneumatic butterfly valve is generally made of stainless steel. The active anions (such as chloride ion and sulfur ion) in the medium are easy to destroy the stainless steel passive film, showing small corrosion holes on the base metal, which is the active center generated by pitting corrosion. The external potential of the metal inside the etch hole is relatively negative, and the external potential of the metal outside the etch hole is relatively positive, so an active passive micro galvanic corrosion cell is formed inside and outside the etch hole. The cell has the structure of large cathode and small anode area ratio, and the anode current density is large, and the etch hole deepens quickly.
3. Fatigue failure
Under the dynamic working condition, the pneumatic butterfly valve is often damaged by fatigue cracks under the cyclic load. Such destruction is normal failure. In order to extend the service life, it is necessary to ensure that the hose design and selection are correct, the device is accurate, and no additional stress such as twisting occurs to the hose.
4. Water hammer phenomenon
Water hammer phenomenon is a pressure transient process caused by sudden change of medium activity state and sudden change of fluid momentum in the pipe. It is a special oscillation phenomenon caused by unstable activities in the pipe. When the pressure wave of sharp rise and fall is transmitted through the pipeline, it will produce a noise similar to that generated when hitting the pipeline with a hammer, so it is also called "water hammer with two edges and one edge". When water hammer occurs, the impact on the elbow section of the pipeline becomes more intense. Therefore, the user should follow the requirements of the operating procedures, such as slowly heating, steadily pressurizing, reducing the change of instantaneous flow and pressure, and preventing water hammer.
5. Escort media
If the escort medium in the hose has chemical properties (acidic or alkaline) and is prone to electrochemical reaction, the material of each part of the hose shall be selected reasonably according to the corrosion resistance parameter table of the hose material.
In addition to the above, the life of the pneumatic butterfly valve will also be affected by the thermal contraction, external vibration and shock, alternating working conditions, short and regular monitoring and maintenance, and inadequate management.