Butterfly valve, also known as flap valve, is a simple control valve, which can be used for the on-off control of low-pressure pipeline medium. It refers to a valve whose closing piece (disc or butterfly plate) is a disc and rotates around the valve shaft to open and close.

The valve can be used to control the flow of air, water, steam, various corrosive media, mud, oil, liquid metal and radioactive media. It is mainly used to cut off and throttle the pipeline. The opening and closing part of butterfly valve is a disc-shaped butterfly plate, which rotates around its own axis in the valve body, so as to achieve the purpose of opening and closing or adjustment.

Double eccentric butterfly valve is also called high-performance butterfly valve, which is mainly used for drainage of water plant, power plant, steel plant smelting, chemical industry, water source spring project, environmental facilities construction and other systems, especially for water pipeline, as regulating and closure equipment. Compared with the center line butterfly valve, the double eccentric butterfly valve is more resistant to high pressure, has longer service life and good stability Compared with other valves, the larger the diameter, the lighter the material and the lower the cost. But because there is a butterfly plate in the middle, the flow resistance is large, so the butterfly valve smaller than DN200 is of no great significance.

Cast iron butterfly valve is also called flap valve. Its opening is basically linear with flow. If it is used to control the flow, its flow characteristics are closely related to the flow resistance of the pipeline. For example, the caliber and form of the valve installed on two pipelines are the same, and if the pipeline loss coefficient is different, the flow of the valve will be very different.