Valve, Fuel Fill Check: Operation: Operation
WARNING: This page is about a different car, the 2012 RAM Pickup and 2012 RAM Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
The one way check valve allows the on-coming fuel to pass through the receptacle. The valve closes when there is no pressure introduced. Both valves are used to keep fuel from escaping from the fuel fill receptacle (fuel supply will only travel toward fuel cylinders).