Engine Running

The charcoal canister is connected to carburetor or throttle housing by a hose which contains the purge valve. When engine is running and vacuum in purge line exceed 0.9 - 1.4 in. Hg, the purge valve opens and vapors stored on charcoal can be drawn into the intake system.

As throttle plate opens, two purge bores (which end in a common passage) are exposed to venturi vacuum. This results in metered purging during light loads (partial throttle). At idle or coasting, these two bores are on atmospheric side of throttle valve, the purge valve is closed and no purging results.