The butterfly plate of butterfly valve is installed in the diameter direction of pipeline. In the cylindrical passage of the butterfly valve body, the disc-shaped butterfly plate rotates around the axis, the rotation angle is between 0 ° 90 °. When it is rotated to 90 ° the valve is fully open.

　　Butterfly valve is simple in structure, small in volume light in weight, only consists of a few parts. Moreover, the valve can be opened closed quickly only by 90 ° rotation, the operation is simple. At the same time, the valve has good fluid control characteristics. When the butterfly valve is in the fully open position, the thickness of the butterfly plate is the resistance when the medium flows through the valve body, so the pressure drop through the valve is very small, so it has good flow control characteristics. Butterfly valve has two sealing types: elastic seal metal seal. Elastic seal valve, seal ring can be embedded in the body attached to the butterfly plate around.

　　The service life of the valve with metal seal is generally longer than that with elastic seal, but it is difficult to achieve complete seal. Metal seal can adapt to higher working temperature, while elastic seal is limited by temperature.

　　If the butterfly valve is required to be used as flow control, the main thing is to the correct size type of valve. The structure principle of butterfly valve is especially suitable for making large diameter valve. Butterfly valve is only widely used in petroleum, gas, chemical industry, water treatment other general industries, but also used in the cooling water system of thermal power station.

　　There are two kinds of butterfly valves in common use, namely, clamp type butterfly valve flange type butterfly valve. Clip on butterfly valve is to connect the valve between two pipe flanges with stud bolts. Flange butterfly valve has flange on the valve, both ends of the valve are connected to the pipe flange with bolts.