What is the working principle of float valve?

The float always floats on the water. When the water surface rises, the float also rises. When the drift rises, the connecting rod also rises. The connecting rod is connected with the valve at the other end. When it rises to a certain position, the connecting rod supports the rubber piston pad to close the water source. When the water level drops, the float also drops, and the connecting rod drives the piston pad to open.