4. FO and FC of pneumatic control valve
There are two types of action of pneumatic control valve: air to open and air to close.

1. Function and structure of pneumatic butterfly valve:
According to the needs of operation and maintenance of hydropower station, in the water diversion system of hydraulic turbine, the corresponding gate or valve is usually installed on the water diversion pipe of hydraulic turbine or in front of the spiral case, and the valve installed in front of the spiral case of hydraulic turbine is called the inlet valve, and the butterfly valve is a commonly used inlet valve. The butterfly valve is mainly composed of a hydraulic ring servomotor, a bypass valve, a cylindrical valve body, a valve rotating around the shaft in the middle and other parts. Under the action of the hydraulic ring servomotor, when the butterfly valve is closed, the circumference of the valve contacts the valve body and closes the water flow path; When opened, the valve is parallel to the water flow direction, and the water flows around both sides of the valve. Compared with other types of inlet valves, the butterfly valve has the advantages of simple structure, small size, light weight, low cost, convenient operation, etc. Its disadvantage is that the valve affects the flow pattern and has large hydraulic loss. Among the components of the butterfly valve, the hydraulic ring servomotor is the main component of the operating valve, and its working performance will directly affect the safe and stable operation of the hydro generator unit.