A butterfly valve is a valve which can be used for isolating or regulating flow. In operation, the valve is fully open or closed when the disc is rotated a quarter turn. Butterfly valve can be used to control the flow of air, water, steam, corrosive media, mud, oil, liquid metal and radioactive media and other fluids.

The closing mechanism takes the form of a disk. When the valve is closed, the disc is turned so that it completely blocks off the passageway. When the valve is fully open, the disc is rotated a quarter turn so that it allows an almost unrestricted passage of the fluid. The valve may also be opened incrementally to throttle flow.