A ball valve (often called a quarter turn valve) is a valve that opens by turning a handle attached to a ball inside the valve. The ball has a hole, or port, through the middle so that when the port is in line with both ends of the valve, flow will occur. When the valve is closed, the hole is perpendicular to the ends of the valve, and flow is blocked. Ball valves may be made of metal, ceramic, and/or plastic. The ball may be chrome plated to make it more durable. A full port ball valve has an oversized ball so that the hole in the ball is the same size as the pipeline resulting in lower friction loss. A standard port ball valve is usually less expensive, but has a smaller ball and a correspondingly smaller port. Manually operated ball valves can often be closed quickly and thus there is a danger of water hammer. Some ball valves are equipped with an actuator that may be pneumatically or motor operated.

There are also three way ball valves, with a T shaped hole through the middle. With such a valve the flow can be directed to either one or the other or both sides or be closed off completely.