Ball valve is mainly used to disconnect or connect the medium and can also be used to adjust and control the fluid. V type ball valve can carry out the relatively precise adjustment and control of flow volume, while three–way ball valve is used to dispatch the medium and change the flow direction of the medium. Compared with other types of valves, ball valve has the following advantages: The fluid resistance is small, and ball valve is the one which has the smallest fluid resistance among all types of valves, even the fluid resistance of the necking ball valves is quite small. The process of opening and closing is fast and convenient. As long as the valve stem rotates 90 degrees, the ball valve completes the total opening or closing action, which is easy to realize the fast opening and closing.