Fuel Evaporation System: Operation
As fuel expands in tank, fuel laden vapors are forced out of tank through an upper vent port. On all models except Vanagon, vapors flow 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, vapors flow up from fuel tank vent lines into a left and a right expansion tank.
Fuel vapors then flow from an upper vent port on expansion tank (from gravity vent valves on Vanagon), through a control valve, and into the charcoal canister where they are absorbed until manifold vacuum pulls them out of canister for burning.
When the engine is running above idle, a vacuum signal opens control valve and canister vapors are drawn from canister through control valve and into intake manifold for burning.