Air Injection: Description and Operation

The air injection system aids in reducing hydrocarbons (HC) and carbon monoxide (CO) in the exhaust stream by introducing a controlled amount of air into the exhaust gases. The system consists of a belt driven air pump, an air control valve (either a diverter valve, diverter valve and [1][2]air switching valve, diverter/pressure relief valve, or switch/relief valve), rubber hoses, check valves to protect the hoses and other components from hot exhaust gases, and injection tubes.
Some engines do not require the divert function in the diverter valve, therefore, are equipped only with a relief valve. Some engines incorporate an air switching system. The air switching system is designed so that air injection will not interfere with the ability of the EGR system to control NOx emissions. Air is injected at the exhaust ports for a short period during engine warm-up. Air flow is then switched to a point downstream where it will assist the oxidation process in the catalyst.

Fig. 1 Air injection pump with centrifugal filter fan (Typical):

The air pump is mounted on the rear of the engine and is belt driven off the camshaft. Intake air is passed through a centrifugal fan at the front of the pump which separates foreign materials from the air by centrifugal force. Air is delivered to the air injection manifold and check valve tube assembly by a rubber hose through the diverter valve and [1][2]air switching valve, if used.
The only serviceable component of the pump is the centrifugal fan filter, Fig. 1.