Fuel Filler Check Valve
WARNING: This page is about a different car, the 2011 Jaguar XKR, 2011 Jaguar XK, 2010 Jaguar XKR, and 2010 Jaguar XK. However, it is still accessible from the selected car via links, so may be relevant.
The fuel filler check valve prevents the escape of fuel through the fuel filler pipe if the vehicle overturns. The fuel filler check valve is installed in a stub pipe in the rear right corner of the fuel tank and sealed with an O-ring seal.
A door on the fuel filler check valve is normally held closed by a spring. During filling, the weight of fuel in the fuel filler pipe is sufficient to open the door and allow fuel into the fuel tank.