A butterfly valve is a type of quarter-turn valve used to control the flow of fluids in large-scale applications. It consists of a disc-shaped element with a pivot axis, which is mounted with a pipe and can be rotated by a handle or actuator. When the valve is open, the disc is turned to a position parallel to the flow, allowing fluid to pass through the pipe. When the valve is closed, the disc is rotated perpendicular to the flow, blocking off the flow of fluid. Butterfly valves are known for their ease of operation, fast-acting nature, and ability to control the flow of a large volume of fluid. They are commonly used in applications such as water treatment, HVAC systems, and industrial processes, and are available in a variety of materials to suit different environments and applications.