The question regarding too much pressure is a good one.  It is, however, not as closely tied to the tube diameter as it is location and orientation.  The vent can act much like a pitot tube and easily capture most if not all of the available ram pressure.  Our wings show visible deformation, even under just one psi.  Lung pressure is enough to see it.  Several years ago added a check-vaIve to one fuel vent to guard against icing.  The mod caused a slight lowering of the vent tube which was canted forward 45 degrees.  In flight I could see the ribs as my skins were bulging under pressure.  Attaching an airspeed indicator to the vent line indicated almost full ram pressure.  I began filing the underside until pressure drop to just a few tenths of a psi.

 

Chris Zavatson

N91CZ

360std