That all depends on the part you are blasting, media being used and the finish you are after.

A good all rounder is 90psi with 1"hose and 60-80 media

The bigger the volume of air being used the easier it is to control, I have a 1/4 " blaster at my unit which is very hard to control, at 130psi it is much less affective than my other 1" system at 90psi!!!

Hope this helps