vent screws
 

I saw the new thommen boards have an automatic pressure vent valve thingy in their boards.

If say you were to leave a normal board out in the sun for a little bit, would it be a good idea to leave the vent screw open to let the expanding air out? or is this not a problem?

I think temperature "may" be a problem, but not so much as a change in atmospheric pressure, which would be a large change in altitude, like when you travel on a aircraft.

I would never think to open the valve just because of sun.

Haven't seen anything on the auto valve you mention, sounds trick !

Unless I'm exposing my boards to higher altitudes (as carvesalot has correctly noted), I never open the vent screws of my boards. Never had a problem of any kind with direct sun on my boards.

However, I do store my boards full time in my white colored van. Also, I should point out that I never leave my boards in their bags exposed to direct sun (bags always stay in the van).