Evaporative Check Valve: Description and Operation
PRESSURE RELIEF/ROLLOVER VALVEAll vehicles have a combination pressure relief and rollover valve. The dual function valve relieves fuel tank pressure. The valve also prevents fuel flow through the fuel tank vent valve hoses should the vehicle rollover. All vehicles pass a 360 rollover.
The pressure relief valve opens at a certain pressure. When fuel tank pressure increases above the calibrated pressure, the valve opens to release fuel tank vapors pressure. The charcoal filled evaporative canister stores the vapors.