Air Injection: Description and Operation

AIR INJECTION SYSTEM

Fig. 1 Air Injection System Components - Typical:

The air injection system is used on heavy duty cycle (HDC) gas engines only. The air injection system consists of:
- A belt-driven air injection (AIR) pump
- Two air pressure relief valves
- Rubber connecting air injection hoses with clamps
- Metal connecting air tubes
- Two one-way check valves
- A replaceable injection pump air filter (this engine only)

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. 3 Air Inlet And Air Pump Air:

Air is drawn into the pump through a rubber tube that is connected to a fitting on the air injection pump filter housing. Air is drawn into the filter housing from the front of the vehicle with rubber tube. This tube is used as a silencer to help prevent air intake noise at the opening to the pump filter housing. An air filter is located within the air pump filter housing.

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. 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 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 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).

AIR INJECTION PUMP

Fig. 4 Air Injection Pump Mounting - Typical:

The air pump is mounted on the front of the engine and driven by a belt connected to the crankshaft pulley.

Refer to Air Injection System Description and Operation for information.