A Butterfly Valve is typically used to regulate a fluid flowing through a section of pipe. The Valve is similar in operation to a Ball Valve. A plate or disc is positioned in the center of the pipe. The disc has a rod passing through it that is connected to an actuator on the outside of the Valve. Rotating the actuator turns the disc either parallel or perpendicular to the flow.

Unlike a Ball Valve, the disc is always present within the flow, therefore a pressure drop is always induced in the flow, regardless of Valve position.