A float valve is a mechanical device used to control the flow of liquids in various applications, such as in water tanks and toilets. It operates by using a buoyant float that rises and falls with the liquid level. When the float reaches a certain height, it triggers the valve to close, stopping the flow of water, and when the level drops, the valve opens again to allow more water in. Float valves are commonly found in systems like toilet tanks, water storage tanks, and irrigation systems. They help maintain a consistent liquid level, preventing overflow and ensuring efficient water usage.