What is the original model number of an M20?

[Doctor Hue]

I've read that an M20 concentrator has been modified. What was the original model number? I have an M20 that was broke, which I have since fixed. (That's another story). But in the meantime, I bought a M600 (Respironics Millennium 5lpm). When I torch with that there isn't much of a difference between the two concentrators. They are very similar inside. The M20 has a small holding tank between the sieve bed and the lpm gauge, which the M600 doesn't. The M600 has what looks like a filter between the compressor and the sieve bed, but the M20 doesn't. There is a copper pipe in place of it, so you can tell the filter has been taken out. The compressors in both look exactly alike, but have different part numbers. The M20 has a Rietschle Thomas model 100-675-00 and the M600 has a Rietschle Thomas model 670CE72-979 N. I tried to find out the specs for both, but am having trouble finding the them. There are a lot of them out there for sale, if you search Thomas 100 or Thomas 670 compressor.

An M20 is 10lpm and 20psi, but where is it 20psi at? If I remember correctly, the manual said to adjust the output to 4 to 7 psi with the pressure regulator. Is the 20 psi at the output of the compressor? It's not the output of the concentrator - at least not on my M20. You can barely feel anything coming out.

The pressure regulator on the M20 was cranked up almost all the way. The M600 was at the lower range of the adjustment. After hooking up the sieve output of the M600 to the input of the 10lpm gauge of the M20, I adjusted the pressure regulator on the M600. There is more pressure on that then there was on the M20. I'm not sure how pure the oxygen was at that point, but the alarm on the M600 didn't go off.

Anybody have any experience with the M600? I'm thinking of adjusting the M600 to match the pressure of the M20 and hooking them together. Thanks, Tom