Air Bypass Valve & Differential Vacuum Valve

These two types of valves are used for the same purpose - to prevent backfiring in the exhaust system during sudden deceleration. When the valve senses a sharp rise in intake manifold vacuum, it opens to allow air from air pump to vent to atmosphere. In addition, some bypass valves also act to prevent high exhaust temperatures under certain engine load conditions. This type of valve will vent injection air to the atmosphere.