Butterfly Valves

A butterfly valve is a quarter-turn valve that uses a rotating disc to control or shut off the flow of a fluid. The "butterfly" is the disc itself, which is mounted on a rod. When the valve is fully open, the disc is turned parallel to the flow, allowing a near-unrestricted passage. To close the valve, the disc is rotated 90 degrees to a position perpendicular to the flow, blocking it completely.