EGR Valve: Description and Operation

Negative Backpressure EGR Valve:

Ported Vacuum EGR:

PURPOSE
The EGR valve is designed to accurately supply exhaust gas to the engine, to reduce NOx (Oxides of Nitrogen) in exhaust emissions. This is done by introducing exhaust gas, which contains very little oxygen, into the intake manifold. This reduces combustion temperatures.


OPERATION
The EGR valve used on this engine is a negative backpressure valve. The amount of exhaust gas flow into the manifold depends on manifold vacuum and variations in exhaust backpressure. The diaphragm on this valve has an internal vacuum bleed hole which is held closed by a small spring when no exhaust backpressure is present. Ported vacuum opens the EGR valve against the pressure of a large spring. When manifold vacuum combines with exhaust backpressure, the vacuum bleed hole opens and the EGR valve closes.
NOTE: The negative backpressure EGR valve will open if vacuum is applied to the valve, with the engine not running.

EGR VALVE IDENTIFICATION

EGR Valve Identification: