Biorb non return valves are designed to prevent leaking water in the unlikely event of power cut, by only allowing the air flow from the air pump to travel one way, back siphoning of the aquarium water is not possible. The valve should be fitted six inches from the air pump. Suitable for use with all BiOrbs except the Classic At least every 6 months a check should be made by disconnecting the air pump and lowering the air line below the water line. In the unlikely event of leakage a one way valve can be fitted to the air line. This should be fitted six inches from the air pump. If you wish to extend the length of the air line from your aquarium it is advisable to do so with a one way valve. Includes 1 metre of airline