When the engine is not operating or during an engine
pop-back, the spring forces the plunger back against
the seat. This will prevent vapors from flowing through
the valve.
During periods of high manifold vacuum, such as idle
or cruising speeds, vacuum is sufficient to completely
compress spring. It will then pull the plunger to the top
of the valve. In this position there is minimal vapor
flow through the valve.
During periods of moderate manifold vacuum, the
plunger is only pulled part way back from inlet. This
results in maximum vapor flow through the valve.
25 - 20
EVAPORATIVE EMISSIONS
WK