If the valve is in a large throttling range, the back of the butterfly valve plate is prone to cavitation, which will increase the possibility of valve damage. Therefore, generally speaking, pneumatic butterfly valves are used outside 15 °.

2、 Examples of valve selection:
The working pressure of the steam pipe is 13kg, the temperature is 350 ℃, and the diameter is 100. What kind of valve should be selected.
From the above known conditions, first determine the material of the valve body. Since the steam pressure is 13 kg and the temperature is 350 ℃, ductile iron or cast steel can be selected. However, considering the temperature of 350 ℃, it is difficult to select nodular cast iron, so in order to ensure safety, cast steel valves should be selected. Then analyze from the pressure. According to the pressure and temperature of the cast steel and the accounting period, the valve should be 16 kg or 25 kg. Next is the selection of sealing surface, which should be made of stainless steel. The given valve diameter is 100, and the pipe diameter is relatively small, so the opening and closing time and torque are not large, so you can choose the manual one. Generally, seamless steel pipes are used for steam supply, and seamless steel pipes are welded. However, in order to make the valve easy to install and maintain, it is recommended to use flange connection.