Our movable mechanical float valves for water tanks act as a filling stop. When the water level in the tank rises/the tank is almost full, the rising float closes the valve for filling. When the water level in the tank drops, the mechanical float opens again, and filling continues. The reliable mechanical float valves for water tanks are therefore mostly used for upright or tower water tanks or for PE tanks with a large volume due to the length of the flexible float arm including the float, as here the float arm has sufficient space to work and only a relatively small tank volume is lost compared to a flat tank. For information on how the float valve works and in which position it opens/closes, please refer to the float valve data sheet on the relevant product page. Our Lids with float valve are another option for regulating the water tank level via a float valve.