I have some drawings but I have no way to post them here. Anyone who has a means of posting them is welcome to them.
The vent system has more than one channel on large transport aircraft and it is standard for the Boeing aircraft to have a pressure relief valve in the surge tank that works to relieve positive or negative pressure in the wing. This valve can be seen inboard of the NACA duct at the wingtip.
The pumps do not pressurize the tank. The fuel tank pumps separate the fuel and air and supply a positive flow of fuel to the engine. The engine fuel feed manifold is the only thing that is pressurized by the pumps. The vent system gives a slight pressure to the fuel in the tanks to minimize fuel sloshing and aeration.
Last edited by Jetdoc; 27th February 2008 at 08:33.
Reason: add info