The ZS/520 range of non-return valves are available in variety of sizes and their function is to permit the free flow of air in one direction only.

Non-return valves are frequently used as protective devices in air circuits. In the event of failure of the air supply upstream of the non-return valve, the downstream side is protected. In some cases an air reservoir is needed as a protected source of air to be used in connection with emergency or fail safe systems and a non-return valve is used to safeguard the reservoir from the normal main air supply.