Air Injection: Description and Operation

Fig 1 Air Injection System Components -- Typical:

The air injection system is used on heavy duty cycle (HDC) engines only.

The air injection system consists of:
- A belt-driven air injection (AIR) pump
- An air pressure relief valve
- Rubber connecting air injection hoses with clamps
- Metal connecting air tubes
- Two one-way check valves

AIR INJECTION SYSTEM OPERATION
The air injection system adds a controlled amount of air to the exhaust gases aiding oxidation of hydrocarbons and carbon monoxide in the exhaust stream. The system does not interfere with the ability of the EGR system (if used) to control nitrous oxide (NOx) emissions.

Fig 2 Inlet For Air Pump:

Air is drawn into the pump through a rubber tube that is connected to a fitting on the air cleaner housing (Fig. 2).

Air is then compressed by the air injector pump. It is expelled from the pump and routed into a rubber tube where it reaches the air pressure relief valve (Fig. 1). Pressure relief holes in the relief valve will prevent excess downstream pressure. If excess downstream pressure occurs at the relief valve, it will be vented into the atmosphere.

Air is then routed (Fig. 1) from the relief valve, through a tube, down to a "Y" connector, through the two one-way check valves and injected at both of the catalytic convertors (referred to as downstream).

The two one-way check valves (Fig. 1) protect the hoses, air pump and injection tubes from hot exhaust gases backing up into the system. Air is allowed to flow through these valves in one direction only (towards the catalytic convertors).

Downstream air flow assists the oxidation process in the catalyst, but does not interfere with EGR operation (if EGR system is used).