Float valves are devices used to control the level of liquid in a tank or reservoir. They operate by using a buoyant float that rises and falls with the liquid level. When the liquid reaches a certain height, the float activates the valve to either open or close, allowing more liquid in or stopping the flow. These valves are commonly found in applications like toilets, water tanks, and aquariums. They help maintain a consistent liquid level, preventing overflow or running dry. Float valves are essential for efficient water management in both residential and industrial settings.