2 Structural characteristics
2.1 The hemispherical body of the hemispherical double eccentric semi pneumatic ball valve adopts the double eccentric design, with reliable sealing effect, instant separation, small torque and long service life. It can be used in the harsh working conditions of conveying granular media. The structure principle is that the center line of the hemisphere is offset from the center line of the valve stem, and offset from the center line of the valve seat. When fully opened, the sphere is completely disconnected from the valve seat, and there is a certain gap. The radius of gyration is divided into long radius and short radius. The tangent line of the rotation track in the long radius will be formed with the sealing surface of the valve seat θ Angle, when the valve is opened and closed, the hemisphere has a gradual separation and gradual extrusion effect on the valve seat surface, thus reducing the mechanical wear and scratches between the valve seat and the hemisphere during opening and closing, and improving the service life.

History and culture of corrugated pneumatic butterfly valve
Pneumatic butterfly valve is an important connecting component in engineering technology, which is separated from corrugated flexible pipe, mesh sleeve and joint. It is used as compensation element, sealing element, connection element and damping element in various gas transmission and infusion pipeline systems, as well as length, temperature, orientation and viewpoint compensation systems, and is used in aerospace, petrochemical, mining electronics, machinery and shipbuilding, medical and health, textile electronics, power construction and other fields. The latest national standard for pneumatic butterfly valves is General Technical Conditions for Corrugated Pneumatic Butterfly Valves.
The corrugated pneumatic butterfly valve is made of austenitic stainless steel or materials required by the user. It has excellent flexibility, corrosion resistance, high temperature resistance (- 235 ℃~+450 ℃), and high pressure resistance (up to 32MPa). It can stop the connection in any direction in the pipeline to compensate temperature and absorb vibration, falling noise, and change the direction of medium delivery To eliminate mechanical displacement between pipes or between pipes and equipment, the double flange metal corrugated hose is particularly suitable for flexible joints of various pumps, valves, etc. with displacement and oscillation.
The history of the research on the technology of corrugated pneumatic butterfly valve Since the German invented and produced the first corrugated pneumatic butterfly valve in the world, after more than 100 years of development, pneumatic butterfly valves have been widely used in aviation, aerospace, nuclear energy, shipbuilding, new construction and other industrial sectors due to their reliable sealing, pressure resistance, upper and lower temperature resistance, corrosion resistance, flexibility and many other functions, It has become an indispensable element in modern pipeline system. With the rapid development of modern industry, the application of pneumatic butterfly valves is increasingly common, and the requirements for pneumatic butterfly valves are also increasingly advanced. The research on the technology of pneumatic butterfly valves must be increasingly deepened. The development of pneumatic butterfly valves can be roughly divided into the following stages.
At the beginning, people formed a tubular structure with animal skin seams to meet the needs of struggle. After a proper long period of time, by the end of the 70th century, the Dutch brothers Wan Delgegin had made a longitudinally stitched canvas hose, which was widely used in fire affairs at that time. Later, with the appearance of rubber in the world market and the development of its vulcanization process, rubber hoses and rubber hoses made of metal wire or hemp rope and other fabrics came out. However, some high-temperature media such as steam and hot air are used in engineering; Low temperature medium such as liquid hydrogen, liquid oxygen and liquid helium; Corrosive media such as gasoline, kerosene, acid, alkali, etc., if transported with rubber hose, of course not. Especially under high temperature conditions, it is more difficult to ensure its safety and reliability.
Therefore, people gradually concentrated their attention on the corrugated pneumatic butterfly valve. The various shapes of the corrugated pneumatic butterfly valve make its surface and inner surface have corresponding ripples. In this way, it not only has the same flexibility as the rubber hose, but also has the functions of high temperature resistance, low temperature resistance, aging resistance and corrosion resistance. Therefore, the metal bellows, as the body of the pneumatic butterfly valve, went into action in this way.