Evaporative Emissions System: Description and Operation

An evaporative emission control system is used to store fuel vapor and prevent release to the atmosphere. The vapors generated in the fuel tank while driving or while the engine is not running, pass through a 2-way check valve and enter the charcoal canister where the charcoal absorbs and stores the fuel vapor. While the engine is running, the fuel vapor stored in the canister is drawn into the intake manifold together with fresh air to be burned. While the engine is not running, the fuel vapor is stored in the canister. The 2-way check valve is provided to keep the pressure in the fuel tank constant. When the pressure in the fuel tank becomes positive and reaches its specified value, it opens the valve to let the vapor into the charcoal canister. On the other hand, when the pressure in the fuel tank becomes negative and reaches its specified value, it opens the valve to let air flow into the fuel tank.