SpectraPure Model ASOFKPositive shut-off; completely shuts off all waste and product waterThe Auto Shut-Off Float Kit is not recommended for evaporation replacement in aquariums. For these applications we recommend either the SpectraPure Automatic Liquid Level Controllers: Single Tank Liquid Replenisher.Includes:Auto Shut-Off (ASO) Valve. Pressure-operated device that shuts off the water supply to the RO membrane when the product line pressure equals 2/3 of the supply line pressure.1# Check Valve. Prevents pressure in the product water line line from leaking back into the RO membrane.Float Valve. Installed in conjunction with the ASO valve. shuts off product water going into the open reservoir.