Fuel Limit Vent Valve (FLVV)
WARNING: This page is about a different car, the 2017 Jaguar XJ, 2016 Jaguar XJ, 2015 Jaguar XJ, 2014 Jaguar XJ, and 2013 Jaguar XJ. However, it is still accessible from the selected car via links, so may be relevant.
The Fuel Limit Vent Valve (FLVV) is located in the upper half of the tank and is connected into a separator which is connected to the tank breather. The main purpose of the FLVV is to control the fill volume of the tank.
During filling, air trapped inside the tank and a small amount of vapor is passed via the FLVV to the tank breather. The air and vapor mix then vents to atmosphere through the breather. During filling, when the tank reaches its full level, the FLVV closes and prevents air/vapor passing through to the tank breather. The resulting back pressure causes refueling to stop automatically.
The FLVV is always open when the fuel tank is below full, providing an unrestricted air/vapor outlet to the tank breather.