The air check valve prevents backflow of water caused by aquarium drawdown, thus maintaining the function and lifespan of the CO2 cylinder. NOTE: For use with steel CO2 pressure vessels only. Do not use with oxygen pumps or DIY equipment as the pressure is not sufficient to operate the valve. When the air check valve is used on an ozone generator, it may prevent ozone from returning to the pump and corrode the impeller. The aquarium check valve protects the motor head from backflow caused by a power outage. This simple check valve is easy to install, requires no additional tools, and can be positioned anywhere in seconds. These stainless steel one-way check valves are suitable for CO2 supply systems in aquariums, fish tanks, etc.