A float valve is a simple controller to which responds to changes in fluid level. It can also be called a liquid level controller. The float valve will open or close according to its use required.
A well known float valve is a ballcock float valve which is a mechanism for filling water tanks, animal water troughs and is also found in flush toilets. The ballcock valve is connected to a hollow sealed float by means of a lever, mounted near the top of the tank. The ballcock valve is connected to the water supply and it is either opened or closed by the lever which has the float mounted at the end. The water level is pre-set and once the valve rises to this level the mechanism will force the lever to close and therefore also close off the water flow.