First post. Hopefully somebody might be able to help.
As per the attached picture, we have a diesel generator day tank which is gravity-fed from a larger, higher storage tank. We also have a vent extending upwards from the day tank, as shown. The day tank has all other bungs properly sealed. I would like to understand the physics involved on why the fuel does not spill out from the vent given the higher level/capacity of the storage tank, especially when filling the larger tank by pump. Hopefully, we can apply the same principles to various set-ups.