Air Injection: Description and Operation

Fig. 1 Air injection pump with centrifugal air filter:

Fig. 2 Diverter or air by-pass valve with integral pressure relief valve.:

All air injection systems consist of an air injection pump, air injection tubes (one for each cylinder), a diverter or air by-pass valve, check valves (two on V6 and V8 engines), air manifolds, tubes and hoses necessary to connect the various components.
Carburetors and distributors for engines with an air pump system are designed particularly for these engines. Therefore, they should not be interchanged with or replaced by a carburetor or distributor designed for an engine without an air pump system.
The air injection pump, Fig. 1, compresses the air and injects it through the air manifolds, hoses and injection tubes into the exhaust system in the area of the exhaust valves. The fresh air ignites and burns the unburned portion of the exhaust gases in the exhaust system, thus minimizing exhaust contaminations.
The diverter or air by-pass valve, Fig. 2, when triggered by a sharp increase in manifold vacuum, shuts off the injected air to the exhaust port areas and prevents backfiring during this richer period. On engine overrun the total air supply is dumped through the muffler or the diverter or air by-pass valve. At high engine speeds the excess air is dumped through the pressure relief valve when the pressure relief valve is part of the air pump, Fig. 1, and through the diverter or air by-pass valve when the pressure relief valve is part of the diverter or air by-pass valve, Fig. 2.
The check valve or valves prevent exhaust gases from entering and damaging the air injection pump, as back flow can occur even under normal operating conditions.
When properly installed and maintained, the system will effectively reduce exhaust emissions. However, if any system components or any engine component that operates in conjunction with the air pump system should malfunction, the exhaust emissions might be increased. These air pumps are not serviceable and must be replaced as a unit.