Exactly kevmor99, the gun "reduces" the PSI to 10 at the cap. As far as what to set the gun at, it really depends on the gun. This Porter-Cable I assume is a Taiwan copy of a name brand like SATA or Binks. SATA NR2000 for instance has an inlet PSI setting of only 29 lbs. While a Sharpe SGF98 has an inlet pressure of 50 lbs, quite a difference. So if you have no starting point, you have to just go by ear.
