Air Injection Check Valve: Description and Operation

The air check valve protects the air pump from harmful reverse flow of hot exhaust gases. The check valve contains a spring-type metallic disc or reed that closes the air line under exhaust back pressure. Check valves are located between the air manifold and the diverter or control valve.
If exhaust pressure is higher than air injection pressure, or if the air pump fails, the check valve spring closes the valve to prevent reverse flow of exhaust.