A ball valve is a quarter turn (rotary) valve with a spherical ball and a round or a specially shaped (characterized) opening of the ball. 

Ball valves can be used as shutt-off valve or as flow control valves. The ball valve can be used with clean or dirty fluids since the ball rotates against the body, peeling debris and cleaning itself. However, if the ball is scratched or galled, the valve can leak when closed. Leak tight closure is therefore limited in practice to clean fluids. 

Ball valves are mainly used in industrial processes as well as in the fields of water supply and water treatment applications to provide on/off capabilities or control duties in particular cases.