Evaporative Emissions System: Description and Operation

Fig. 10 Evaporative Emission Control System:

Fig. 11 Evaporative Emission Control System Operation:

The evaporative emission control system is designed to prevent raw fuel vapors from escaping into the atmosphere by the use of a charcoal canister, bi-metal vacuum switching valve (BVSV), a purge port at the intake manifold, and a fuel filler cap. The system holds fuel vapors collected from the fuel tank in the charcoal canister where they are stored until the engine warms to 129° F . The BVSV then opens and allows engine vacuum to open a check valve in the carbon canister. When air is drawn through the canister another check valve inside the canister opens and that pulls air from the fuel tank, this in turn pulls air into the fuel tank through the check valve in the fuel filler cap.