See above for the Butterfly Valve Symbol and diagram which shows an open and closed Butterfly Valve.
The Butterfly disc positioned in the center rotates either parallel or perpendicular to the flow, allowing for quick shut-off. When the valve is fully closed, the disc is turned perpendicular so it completely blocks off the passageway. When the valve of a Butterfly Valve is fully open, it is rotated a quarter turn which is then parallel with the flow. The disc is commonly referred to as the Butterfly which is mounted on a rod. The movement of the rod with the disc will depend on whether the valve is open or closed.
