2 Overview and trend of relevant technologies at home and abroad
2.1 Introduction to the use of high-end valves in the power plant The high-end valves used in the thermal system of the power plant work in a high-temperature and high-pressure parameter environment, which requires high reliability for the automatic control of high-end valves. As the research and manufacturing of high-end valves in China is still in the technical breakthrough stage, the high-end valves used in China currently mainly rely on foreign imports, and the import quota of high-end valves of domestic power plants alone each year exceeds 10 billion yuan. Therefore, it is of great significance for China's equipment manufacturing industry to introduce, digest and absorb the technology of world famous valves. Among them, the small high-temperature and high-pressure metal seat pneumatic ball valve should be the first to realize localization. This project can not only bring considerable economic benefits for power plant energy conservation, but also have huge promotion space in the power industry.
2.2 Development of supersonic thermal spraying technology Thermal spraying methods can be divided into combustion method and electrothermal method. Combustion method includes flame spraying and explosive spraying; Electric heating method includes arc spraying and plasma spraying. Now there have been supersonic flame spraying, supersonic plasma spraying, laser spraying, reactive thermal spraying, cold spraying and other processes.
(l) Supersonic flame spraying. The High Velocity Oxygen Fuel (HVOF) method mainly uses a high-pressure water-cooled reaction chamber and a slender injection pipe to send fuel (kerosene, acetylene, propylene and hydrogen) and oxygen into the reaction chamber for combustion, generating a high-pressure flame, which is compressed by the injection pipe and accelerates the injection. The sprayed powder can be delivered axially with high pressure or from the side of the injection pipe. The other method is to inject fuel (kerosene, acetylene, propylene and hydrogen) and oxygen through high pressure, burn them outside the nozzle, shoot the sprayed powder axially into the flame from inside the nozzle with high pressure gas, then compress and accelerate the combustion flame through the compressed gas in the air hood outside the nozzle, and spray the molten powder to the substrate. This method is characterized by high jet velocity, lower flame flow temperature than explosive spraying, and is suitable for carbide coating. The highest density of the coating obtained by supersonic flame spraying can reach 99.9% of the theoretical density, and the strength can reach more than 70MPa; In addition, there are few impurities in the coating, and the residual stress of the coating is small. In some cases, the designed residual stress can be obtained. Therefore, thicker coatings can be sprayed, and the spraying efficiency is high. But it also has the disadvantages of high fuel consumption and high cost.

1. Fluid resistance pneumatic ball valve is one of the smallest fluid resistance in all valve categories. Even the reduced diameter pneumatic ball valve has relatively low fluid resistance.
2. The thrust bearing reduces the friction torque of the valve stem, which can make the valve stem operate stably and flexibly for a long time.
3. The sealing performance of the valve seat is good. The sealing ring made of elastic materials such as polytetrafluoroethylene is easy to seal, and the sealing capacity of the pneumatic ball valve increases with the increase of the medium pressure.
4. The valve rod seal is reliable. Because the valve rod only operates as if it is rotating rather than lifting, the packing seal of the valve rod is not easy to be damaged, and the sealing capacity increases with the increase of the pressure of the medium
5. Since materials such as polytetrafluoroethylene have good self-lubricating property and small friction loss with the ball, the service life of pneumatic ball valve is long.
6. Anti static function: set a spring between the ball, valve stem and valve body, which can lead out the static electricity generated during the switching process.
7. The lower mounted valve stem and the convex step at the head of the valve stem prevent the valve stem from ejecting. If the valve stem seal is damaged due to fire, metal contact can also be formed between the convex step and the valve body to ensure the valve stem sealing.