Will depend some on which beergas blend you have, the beer temp, carb level, and line length, but ~30 psi is pretty common. You'll want to carb with CO2 first (or prime to carb), and then just use the beergas to serve. I'd also suggest keeping the carb level below 2 vol.
I'm trying to find some porn filmed by a dog wearing a GoPro. - SharonaZamboni