Butterfly valve 

• the butterfly valve is installed with the valve stem oriented vertically with the actuator directly above it, but in some cases, the stem is situated horizontally instead
• A butterfly valve is a type of valve that can control or stop the flow of a fluid by rotating a disk-shaped closing mechanism. The disk is attached to a rod that can be turned by a handle, a gear, or an actuator.
• The “butterfly” is a disk connected to a rod. It closes when the rod rotates the disc by a quarter turn to a position perpendicular to the flow direction. When the valve opens, the disk is rotated back to allow the flow
• 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.