For example, pneumatic butterfly valves can be divided into four types according to their structural forms: offset plate type, vertical plate type, inclined plate type and lever type. According to the sealing form, it can be divided into soft sealing type and hard sealing type. The soft seal is rubber ring seal, and the hard seal is metal ring seal. According to the connection form, it can be divided into flange connection and wafer connection. The transmission mode can be divided into manual, gear transmission, pneumatic, hydraulic and electric. 　　　　

Under the condition of high pressure difference and high flow rate, even if the temperature is normal, the characteristics of the material shall be evaluated to make the material satisfy the working condition. Generally speaking, at room temperature, when the pressure difference exceeds 15 bar, the material of valve core and valve seat should be adjusted from 316 to stellite alloy surfacing or alloy with higher requirements. For weakly corrosive media, 420QT (quenching+tempering), 440QT, etc. can be selected. High pressure difference and high flow rate will bring severe erosion or cavitation, which will cause great damage to the valve trim materials. Therefore, the material requirements for the valve body and valve trim are very high. Regarding the valve core, stainless steel surface nitriding (HRC70) treatment should be considered to make it have strong erosion resistance, improve the accuracy of valve flow and service life. The oxidation resistance of materials at high temperature is also a very important parameter. In the process of temperature cycle modification, the selected materials should prevent repeated oxidation of the material appearance, occurrence of oxide skin and other problems. Generally, the materials of austenitic stainless steel, hard alloy and special alloy have good high-temperature stability, and suitable materials can be selected according to different high-temperature conditions.