Anti-AFTERBURN System: Operation
The anti-afterburn valve is sensitive only to sudden increases in vacuum. The length of time it stays open is controlled by a diaphragm that senses change in manifold vacuum.
When manifold vacuum suddenly increases, as during sudden deceleration, diaphragm/valve unit is pulled downward. Air flow from air chamber to sensing chamber is restricted by an orifice, creating a pressure differential on diaphragm, which holds valve open.
This unbalanced condition lasts for a few seconds until pressure in both chambers is equalized by air entering through orifice. When both chambers are equalized, spring pressure pushes diaphragm up, closing valve.