Butterfly valves are a rotary motion valve that is used to stop, regulate, and start fluid flow. In the quarter-turn family, butterfly valves consist of a metal disc mounted on a rod. Butterfly valves are easily and quickly operated because, like a ball valve, 90º rotation of the handle moves the disc from a fully closed to a fully opened position. Larger butterfly valves are actuated by handwheels connected to the stem through gears that provide mechanical advantage at the expense of speed. Butterfly valves can be used in a wide variety of applications and are especially well-suited for the handling of large flows of liquids or gases at relatively low pressures and for the handling of slurries or liquids with large amounts of suspended solids. They are built on the principle of a pipe damper. The flow control element is a disc of approximately the same diameter as the inside diameter of the adjoining pipe, which rotates on either a vertical or horizontal axis.