Evaporative Emissions: Introduction

The evaporative emission (EVAP) control system reduces the level of hydrocarbons released into the atmosphere by fuel vapor venting from the fuel tank. The system comprises a charcoal canister, purge valve and interconnecting vent pipes. The vent pipes are connected to the system components using quick release connectors.

Fuel vapor is generated by the fuel in the tank and the amount of vapor produced increases as the fuel heats up. Fuel vapor flows to the charcoal canister through the tank vent pipes, via a liquid/vapor separator.

The vapor from the liquid/vapor separator is absorbed and stored by the charcoal canister. Because there is a limit to the amount of vapor the canister can contain, the fuel vapor is purged from the canister when the engine is running and burned in the engine during the combustion cycle.