Fuel Evaporation System: Notes
The fuel evaporation system is used to reduce emissions of hydrocarbons (HC) into the atmosphere. The system consists of a sealed fuel tank, vacuum relief filler cap, charcoal canister, purge control valve, fuel-check valve, canister purge and vacuum signal lines, and vapor vent lines.
Fuel vapor from the sealed fuel tank is stored in the activated charcoal canister when the engine is not running. Fuel vapor is retained in the canister until purged by air drawn through the bottom of the canister to the intake manifold during engine operation.
When engine is running at idle, purge control valve is closed and only a small amount of stored vapor flows into the intake manifold through the constant purge orifice. As engine speed increases and the throttle vacuum rises higher, the purge control valve opens and vapors are drawn into the intake manifold through the main purge orifice and the constant purge orifice. See Fig 1 , Figure and Figure .