EGR Valve: Description and Operation

Negative Backpressure EGR Valve:

DESCRIPTION
The Exhaust Gas Recirculation (EGR) valve used on this engine is a negative backpressure valve. The amount of exhaust gas flowing into the manifold depends on ported vacuum and variations of exhaust backpressure.

OPERATION
The diaphragm on this valve has an internal air bleed hole which is held closed by a small spring when there is no exhaust backpressure.
Ported vacuum opens the EGR valve against the pressure of a large spring. When ported vacuum combines with negative exhaust backpressure, the air bleed hole opens and the EGR valve closes.