A butterfly valve is from a family of valves called quarter-turn valves. In operation, the valve is fully open or closed when the disc is rotated a quarter turn. The “butterfly” is a metal disc mounted on a rod. 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. Their lightweight structure allows for easy installation and maintenance, making them a popular choice in various industrial applications. The design employs a rotating metallic disc that provides efficient control over the fluid flow, which can be especially useful in systems requiring frequent operation. Furthermore, due to their simple construction, they require less raw material, contributing to their cost-effectiveness.