A ball valve is a flow control device which uses a hollow, perforated and pivoting ball to control liquid flowing through it. It is open when the ball’s hole is in line with the flow inlet and closed when it is pivoted 90-degrees by the valve handle, blocking the flow.
source/image(PrtSc): Hydraulic and pneumatic systems
A ball valve is classed as a quarter-turn shut-off or isolation valve that controls the flow of a liquid or gas by way of a spherical ball with a hole bored through the centre and held into the valve body by two identical seat seals.
Valve bodies are made of metal, plastic, or metal with a ceramic; floating balls are often chrome plated for durability. One disadvantage of a ball valve is that when used for controlling water flow, they trap water in the center cavity while in the closed position.
In the event of ambient temperatures falling below freezing point, the sides can crack due to the expansion associated with ice formation./wikipedia