I just had the motor on my 20 year old compressor go DOA. It's a 20 Gal tank with an approx. 1 hp motor and max PSI of 135. The motor is no longer available through the manufacturer. I replaced it with a Dewalt 15 gal compressor with a 1.6 hp motor with max PSI of 225. Both comps are rated at approx 5 SCFM at 90 psi. The price at the blue box store right now made it not worth trying to source my own motor for the old one. I would have liked to go with a full size upright, but the funds are not available right now.

My first question is, as PSI increases does the actual volume of free air being held increase in a 1 to 1 ratio? Meaning if a tank is holding 200 psi would it have taken in twice the ambient air as a same size tank holding 100 psi given the ambient conditions were identical?

My second question is, the tank on my old compressor appears to be good from the outside, however I have not done an internal inspection. I thought about removing the motor and turning it into a portable storage tank to take on the go. Would it be of any benefit to add it after the compressor to increase the storage of my shop system? Obviously I would have to regulate the PSI down to 135 before the tank. The lines in my shop are only rated at 150 PSI so I have to regulate the new comp down anyway. The old comp was adequate for what I was doing, however I would like to start spraying in the near future.