Choosing a compressor for plasma cutting

The ones with built in variable speed drives are very nice, They just hum along matching speed to demand maintaining a constant pressure, and using a lot less energy. We recently upgraded our shop supply from a few of Atlas Copco GS18 compressors (two vfds and one single speed) to two GA45, 60hp units (one VFD, one single speed). Yes, we use a lot of air, with 3 automated paint lines, numerous sanding booths, and a bunch of air tools and other stuff. I can't imagine doing all that with piston compressors, ick.

I don't know how things are in your countries, but compressors of a single stage have a loss of about 50% from the theoretic air flow per minute. If the compressor is capable of 10 cfm theoretically, you can expect 5 cfm real.

compressors with 2 stages (where the second cylinder takes the output from the first cylinder) have a loss of 30%

screw compressors have near no loss.

screw compressors are better in almost all respects, the air demand must be calculated well, better if they run continuously at the right temperature, otherwise many stops and starts tend to accumulate water in the oil.