F 350 4WD Pickup V8-351 5.8L VIN H EFI (1997)
Rollover Valve: Description and Operation
The evaporative emission valve mounted on the top of the fuel tank is used to control the flow of fuel vapor entering the fuel tank vapor delivery line that
conducts vapor forward to the evaporative emissions canister in normal circumstances. If, due to extreme conditions, excessive pressure is generated
inside the tank, the purge port opens up, allowing fuel vapor to escape to the atmosphere, stabilizing pressure inside the fuel tank. The evaporative
emission valve has a head valve that prevents the fuel tank from overfilling during refueling operation. The evaporative emission valve also has a
spring-supported float assembly, which prevents liquid fuel from entering the vapor delivery tube during severe handling, steep grades or in the event of
vehicle rollover.
