A ball valve is a quarter-turn valve which is a spherical, hollow, perforated and pivoted ball used to operate a ball valve. It act as a floating device to control flow through it. It is used in hydrocarbon process applications and are useful for low-flow situations. Ball valves use a metal ball with a hole bored through the center, sandwiched between two seats to control flow. It's a machine for filling water tanks, while avoiding overflow and backflow.

It consists of a valve which is connected to the float near the top of the tank. The float is often ball-shaped, hence the name ballcock and is connected to a lever. The valve is connected to the incoming water supply, and is opened and closed by this lever.

When the water level rises, the float rises with it; once it rises to a pre-set level, the mechanism forces the lever to close the valve and shut off the water flow and vice versa.

Ball float valves are used for domestic cold water applications. A smaller float valves used in toilet cisterns to measure the flush water. It maintains the level in the cold water header tank by regulating the pressure of the hot water system.