The pressure relief valve can also open to relieve air or fuel pressure if there is too much pressure during refueling."
I can confirm Jetdoc's(?) statement that the (2) surge tank pressure relief valves have both positive and negative pressure relief. There is a description in the AMM on how to check the valve using positive and negative pressures. So the vacuum in tank theory seems to have lost its momentum
On being sanctimonious...
My company does not allow me to take information from company computers without permission.
All the Boeing manuals on my company computers have very prominent copyright statements.
No doubt similar restrictions are placed on those posting pictures here.
Also...
Some of the technology used on the 777 is classified material. Boeing recently got into trouble for selling airplanes to a foreign country.
What copyright
de-restrictions are placed on Americans are not necessarily the same as those placed on other nationalities.
There is a difference between being sanctimonious and worrying about fellow PPRuNers losing their jobs and being punished financially and/or being imprisoned.
Rgds.
NSEU