Boost Controlled Deceleration Device: Operation
The BCDD contains 2 diaphragms. When vacuum in the intake manifold exceeds a predetermined value, diaphragm No. 1 opens the vacuum control valve. This allows manifold vacuum into a vacuum chamber in the BCDD and actuates diaphragm No. 2. When actuated, diaphragm No. 2 opens the air control valve, allowing additional air into the manifold to maintain required operating pressure.
The amount of air entering the manifold is controlled by the servo-action of the air control valve and vacuum control valve. This servo-action maintains manifold vacuum at the predetermined operating pressure.