Fuel Filling

During fuel filling, the fuel vapor displaced from the fuel tank is allowed to escape to atmosphere; valves within the fuel filler prevent any vapor escaping through the charcoal canister as this can adversely effect the fuel cut-off height. Only fuel vapor generated whilst driving is prevented from escaping to atmosphere by absorption into the charcoal canister. The fuel filler shuts off to leave the tank approximately 10% empty to ensure the roll over valves (ROVs) are always above the fuel level and so vapor can escape to the charcoal canister and the tank can breathe. The back pressures normally generated during fuel filling are too low to open the pressure relief valve, but vapor pressures accumulated during driving are higher and can open the pressure relief valve. Should the vehicle be overturned, the ROVs shut off to prevent any fuel spillage.