1 Overview
With the continuous development of the industry, there is an increasing demand for ball valves, especially ball valves under severe conditions of high temperature and high pressure. ball valves are required to have higher performances such as wear resistance, erosion resistance, high temperature resistance, and corrosion resistance. The traditional full-bore ball valve, although the core and valve seat are surface hardened by surfacing, spraying, etc., but its service life, cost and performance still cannot meet the requirements of use, such as industrial silicon, coal chemical industry, blast furnace gas, Harsh working conditions such as gas. The double eccentric hemispherical valve is a new product developed by taking the advantages of different structures of ball valves, V-shaped valves and orbital ball valves. The ball valve adopts a double eccentric sealing structure, which has low wear, small torque, good sealing performance and long service life. The valve seat and hemisphere are treated with a special hardening process, which is especially suitable for the requirements of wear resistance, erosion resistance, corrosion resistance and high temperature resistance under harsh working conditions.

2 Structural features
2.1, hemisphere

 When fully opened, the sphere is completely separated from the valve seat, and there is a certain gap. The radius of gyration is divided into a long radius and a short radius. The tangent to the long-radius rotation track will form an angle θ with the sealing surface of the valve seat. When the valve is opened and closed, the hemisphere has a gradual separation and squeeze effect relative to the seat surface, thereby reducing the valve seat during opening and closing. The mechanical wear and abrasion between the hemisphere and the hemisphere increase the service life.

2.2, valve seat

(1) The valve seat adopts a floating design, which reduces the difficulty of processing and ensures that the center line of the valve seat coincides with the center point of the hemisphere spherical surface, thereby improving the sealing performance. There is a gap between the valve seat and the valve body. The center line can be automatically aligned by using the hemispherical positioning during assembly to ensure full contact between the sealing surface of the valve seat and the spherical surface of the hemisphere, which solves the leakage caused by machining accuracy errors and improves the service performance and life of the ball valve. .

(2) The seal between the valve seat and the valve body adopts a hard seal structure, which is suitable for high temperature and high pressure working conditions. The size c of the sealing contact surface between the valve seat and the valve body is small, and the accuracy of the respective sealing surfaces is high. When assembling, the retainer is installed with an electric impact wrench. Not only the retainer engages with the valve body to prevent loosening, but also the frictional rotation of the valve seat. , In line with the principle of mechanical vibration meshing, so that the valve seat and the valve body are reliably sealed.

(3) The valve seat and the valve body and the valve seat and the hemisphere adopt two-point hard sealing, so the valve can be used in high temperature and high pressure conditions.

2.3. Other parts

The valve adopts modular design as a whole, with simple structure, good reliability and high versatility. The valve stem adopts a blow-out prevention structure. The driving mode is diversified. The connection size of the valve stem, the bracket and the actuator conforms to the ISO5211 standard, and can be directly assembled with various standard actuators. Commonly used driving methods include manual, pneumatic, hydraulic, pneumatic and hydraulic linkage and electric, etc., thereby improving the performance of the double eccentric hemispherical valve.

3 Range of use
The double eccentric hemispherical valve is suitable for the requirements of various general industries, such as water, sewage, waste water, steam, gas, pulp and other media. If the seal pair adopts Cr-Mn-Si cemented carbide and has the functions of fire resistance, explosion protection and anti-static, it is suitable for medium and high temperature medium requirements, such as coal gas, coke oven gas, water gas and natural gas. If the sealing pair (half sphere, valve seat) and the valve body flow passage are treated with a special tungsten carbide process, it will have the advantages of high efficiency and energy saving, good wear resistance, reliable sealing performance, light operation, rapid opening and closing, and long service life. Ideal for valves used on pipelines in the industrial silicon industry. Because of its hemisphere and valve seat instant separation and instant compression characteristics, it is suitable for harsh working conditions with particles in the medium. It can be widely used in blast furnace pulverized coal injection, pulverizing system and dust removal system in metallurgy, mineral processing, electric power and other production processes. Various pipeline control in the. In the process of instant detachment and instant compression, the hemisphere and the valve seat have the effect of squeezing and cutting, which can remove the scale and adhesion on the sealing surface, and can ensure the tightness and reliability of the seal. It is the ideal choice for the valve for conveying two-phase mixed fluid medium in technological processes such as solution slurry, slurry ash slag, etc., which are easy to precipitate and scale, crystallize.

4 Conclusion
At present, multiple specifications of double eccentric hemispherical valves have been applied to various projects in different industries, with good results, and gradually expanding the scope of use.