[Kevin Sevcik]

I should do up a tutorial/whitepaper on this to save people time and annoyance, probably. It mostly comes down to Boyle's Law: P1 * V1 = P2 * V2. Short-ish version:

First off, you don't use all the air in your tanks. Not unless you have actuations that require no force. Tanks at 1 psi do almost nothing, right? So let's assume you always keep your tanks at or above working pressure. 60 psi is the usual, though as we'll see, lower pressures can be better.

So you have a 1 gal tank at 120psi. Boyle's law says 1 gal at 120psi = 2 gal at 60psi. But you can't use all 2 gal. You have to leave 1 gal in the tanks at all times because you don't have a magic gnome making your tanks smaller to squeeze the air out. So storing 1 gal at 120psi mean you can use 1 gal at 60 psi. That's where lower working pressure helps, you leave less air in the tanks. I'll let you work out those details.

So on to compressors. The flow rate stats you see listed on the compressor page say CFM. You might think that's a cubic foot of air at whatever pressure is listed there, but no. I confused myself that way once before I sanity checked and realized that meant things got more efficient at higher pressures. No, what they mean is SCFM. Standard Cubic Feet per Minute. That's a cubic foot of air at 1 atmosphere gauge, or 14.7 psig.

And we're back to Boyle's law. I was assuming we were pumping at 100psi, since that seemed a reasonable average pressure an air hungry robot would be at most of the time. At 100psi, the 100C pushes 0.52 SCFM, the 330C-IG pushes 0.60 SCFM. So 0.08 SCFM difference, for 0.16 SCF a match = 1.2 gal at 14.7 psi = 0.29 gal at 60psi. And that's where the number comes from.

Lots of my other estimates like the 2.2 gal per match total for the 330C-IG work similarly converting air at 14.7 psi to air at the 60 psi you likely would use it at. I'll grant that everything gets changed drastically if you're working at 45psi, or 30 psi. I'm seriously doubting an air hungry robot is working at those pressures however, since using a 2x multiplier cylinder at 30 psi is heavier than a 1x multiplier at 60 psi. Plus you can pull more air out of a tank at a lower working pressure, so your storage is more efficient and you're less likely to need a pump in the first place.