Mounted on the side of the plenum chamber at the rear of the engine, the connection face (CF) must be airtight. A trace of "instant gasket" when fitting may be used. Sufficient air is provided by this valve during engine Overrun conditions to ensure good combustion.
This is necessary because the very high vacuum during rapid deceleration of the engine causes any residual fuel condensed on the inlet manifold and plenum chamber walls to evaporate and create an over rich mixture.
The pressure differential acting on the valve head (VH) compresses the spring (SP) centralised by the spring seats (SS). Thus, the head moves away from the valve disc (VD) which is trapped by the connection faces.
This allows metered air to pass from the air rail into the inlet pipe (IP) and through the valve into the plenum chamber to optimise the combustible mixture.
A nut (N) adjustment controls the spring tension, which is preset during manufacture and should not be altered. However, if it has been disturbed, acceptable conditions can be restored with the nut approximately 5 turns out from fully closed.
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