A ball valve is a type of shut-off valve that uses a hollow, perforated, and pivoting ball to control the flow of gas or liquid. The valve is opened or closed by a handle or actuator that rotates the ball 90 degrees. When the handle is turned so the hole in the ball aligns with the flow, the valve is open. When the handle is turned 90 degrees, the solid part of the ball blocks the flow. This quarter-turn operation allows for quick and reliable shut-off.