Compared with conventional gate and globe valves, butterfly valves achieve high performance near to perfection with its pressure resistance and durability. Especially in vessels, the Butterfly Valves enjoy high reliability and when compared with the conventional valves, the Butterfly Valves are excellent in the following aspects: (1) light and compact, (2) maintenance is easy, (3) labour-saving ease of operation, and (4) low cost. 2. Worm Gear Actuator: Gear reduction is available by the worm and worm wheels incorporated, opening the disc very lightly, leading to non-step adjustment of flow. In addition, a stopper bolt is fitted to the fully closed and fully opened positions, hence accurate positions can be taken. Furthermore, the opening angle of the disc can be read by the indicator at the upper part of the gear box. "Close" is effected by revolving clockwise, and "Open" by revolving anticlockwise, with the manual handle.