Fuel Evaporation System: Description
Toyota fuel evaporation control system is designed to prevent the escape of raw fuel vapors into the atmosphere. This is accomplished with a special fuel tank, filler cap, charcoal fuel vapor storage canister(s), and various control valves (depending on vehicle application).
When fuel vapor pressure builds in tank, a check valve in canister opens and vapors flow into canister for storage. When vacuum forms in tank, a check valve in canister opens and stored vapors are drawn into fuel tank. If fuel tank vacuum should increase above a pre-set level, a vacuum relief valve opens in filler cap and fresh air flows into fuel tank preventing tank collapse.