The air check valve can prevent the aquarium from backflowing water which is caused by the decrease, and keep the function and service life of the carbon dioxide cylinder. NOTICE: Only used for carbon dioxide steel pressure vessels and can not be used for DIY and oxygen pumps because the pressure is not enough to operate the valves. When used in the ozone generator, the air check valve can prevent the ozone from backflowing to the air pump and eroding the propeller. The aquarium check valve can protect the power head from backflow of water caused by power failure. The simple check valve is easy to install, requires no additional tools, and can be fixed to any place you want in seconds. These one-way check valves stainless steel are suitable for CO2 supply system in aquariums, fish tank and others.