NSEU
Can't find any reference to vent negative pressure relief regarding the surge tank vent valve in the Boeing 777 Maintenance Manual D&O. Is it mentioned in the (proper) AMM? Wouldn't the float valves normally provide negative px relief?
AMM 28-10-00 p17/19 shows the surge tank pressure relief valves.
Boeing says..If a pressure difference opens the valve.. I assume this means either way.
By the way, posters that ask for details of the fuel system. The Boeing manuals are copyright and I am not posting them here.