This is another type of flow control valve. It consists of a large disk which is rotated inside a pipe, the restriction in flow being determined by the angle. Figure 6.30 shows a simple design of a butterfly valve.
The advantage with this valve is that it can be constructed to almost any size. These valves are widely used for controlling gas flow. But a major problem associated with these valves is the high amount of leakage in the shut-off position.