Fuel Tank Pressure Release Valve: Description and Operation

Pressure Relief/Roll Over Valve:

The dual function pressure relief/rollover valve, mounted on top of the fuel tank, relieves fuel tank pressure under normal operating conditions, and prevents fuel flow to the vapor canister through the vent hose in the event of a vehicle rollover. The valve consists of a plunger, spring, and orifice with guide plate, and is mounted on top of the fuel tank in a normally open position. In the open position fuel vapors from the tank travel to the vapor canister. In the event of rollover the valve becomes inverted and the plunger is forced against the guide plate, preventing raw fuel from flowing through the valve orifice into the vent tube.