It is a one way value which allows air flow in and out depending on certain out-side and internal tank pressure. Check value equilizes the pressure in the tank due to vaccum created by diesel suction and and gas pressure due to heat. All gas tanks have them.
The need to expand the tank... Well its my need to modify the original fuel tank space, as I am re-aligning the front seats and am installing the buckets, plus I am lowering the seats and the profile of the upcoming roll-cage to improve the handling of the jeep. I intend to reduce the height of the vehicle by around 3 inches from the top. At the same time lift it by 3 inches from the bottom; hopefully, this will offset the center of gravity difference.
Because of improving the handling characteristics of the jeep, I am re-distributing the fuel accross the vehicle. There will be 2 tanks in the front (underneath the front passenger), and 1 tank in the rear in-place of the exhaust muffler.
After this mod the only issue that I will be left with for improved handling is the camber of the rear wheels. Any ideas???