This device regulates the flow of fuel gasses from the fuel tank when the vehicle is either stopped or running. Normally, the purge valve on the vacuum canister is closed. When the driver turns off the vehicle, gasses from the fuel tank begin to pass into the vacuum canister, which is passed into the charcoal canister. Once the driver starts the engine, the vacuum canister’s purge valve opens and begins to send the fuel vapors to the engine, where it is combusted. Failure can be caused by many things such as a blockage, a damaged vacuum line, or even a disconnect from the intake manifold and the purge valve. All these can cause the vacuum canister to lose pressure and cease functioning.
