Fuel Evaporation System: Operation
As fuel expands in tank, vapor is forced out of tank through an upper vent port. On all models except Vanagon, vapor flows up through a gravity valve and into an expansion tank where liquid fuel condenses and returns to fuel tank as temperature drops. On Vanagon models, vapor flows up from fuel tank vent lines into a left and a right expansion tank.
Fuel vapor then flows from an upper vent port on expansion tank (from gravity vent valves on Vanagon), through a control valve, and into the charcoal canister, where it is absorbed until manifold vacuum pulls it out of canister for burning.
When the engine is running at speeds greater than idle, a vacuum signal opens control valve and canister vapor is drawn from canister, through control valve and into intake manifold for burning.