Not psi. You need a compressor that puts out more volumn, and equals the pressure from your water source usually 60 psi. A tow behind has both so you need to be careful. Where the little one you use you pump up as high as you can and let it go, it loses pressure quickly as the water disperses from the pipe. Then you don't have enough volumn to keep the heads up for long, which will leave more water behind as it drains back to the low spots.
thanks for clearing that up. i've only done a handful (including my own) and haven't had any freeze. i'm sure lots of cfm's is better . thanks