Evaporative Emissions System - BMW: Operation

When engine is off, fuel vapors are collected in vapor storage tank. Some vapors are condensed in storage tank and flow back into fuel tank. Excess vapors continue to carbon canister, where they are absorbed. When engine is started, air flow in air cleaner causes a low vacuum at purge line and vapor is drawn from canister and storage tank, mixed with fresh air, and burned in the engine. As fuel is drawn from fuel tank, flow through control system is reversed and air is drawn into storage tank. Activated carbon canister is equipped with a screen in its bottom surface to permit fresh air to be drawn in to purge carbon. Vapor storage tank also allows for fuel expansion of a completely filled fuel tank.