F 100 2WD Pickup V8-400 6.6L (1982)
Fig.73 - Normally Closed Timed Air Bypass Valve
Fig.74 - Timed Air Bypass Valve With Integral Function
DESCRIPTION
Some 1966-67 vehicles use a bypass type anti-backfire valve in place of the "gulp" type system. The valve operates at all times and all output air
from the air pump is routed through it. The air flow to the manifolds is temporarily interrupted and diverted to the air pump air cleaner during
deceleration.
The air bypass system on 1968-82 vehicles serves the same purpose as earlier types, but three different types of bypass valves are used, depending
on application. These are: a timed bypass valve, a normally closed bypass valve, or a timed bypass valve with an integral vacuum function. They
are mounted "in-line," or on the air pump. Figs. 71, 72, 73, and 74.
On systems using a timed bypass valve, Figs. 71 and 72, during normal operation, vacuum is equalized on both sides of the diaphragm. The
diaphragm return spring holds the valve closed, and allows air to flow to the exhaust ports. During deceleration, the sudden rise of intake manifold
vacuum under the diaphragm overcomes return spring pressure and pulls the valve down. The air flow is then momentarily diverted to atmosphere,
because vacuum is quickly equalized again on both sides of the diaphragm through a small orifice in the diaphragm.
