Evaporative Emission Control Canister: Description and Operation

Fig. 3 Evaporative emission control system carbon canister:

This system limits the emission of fuel vapors to the atmosphere. Fuel vapors trapped in the sealed fuel tank are vented through the orifice in the vapor valve assembly in the top of the tank. The vapors leave the valve assembly through a single vapor line and continue to the carbon canister, Fig. 3, located in the engine compartment, for storage until they are purged into the engine for burning.
Fuel vapors that would otherwise pass directly into the atmosphere are vented to the carbon canister when the engine is stopped. When the engine is started the vapors will be drawn into the engine for burning when the operating mode of the engine can accept the vapors for efficient combustion.