I thought I'd respond to one of Tbone's comments in this thread rather than muddy the waters on the other thread: "...of note, peak efficiency does not mean peak speed. Peak efficiency will be considerably slower than top speed, no different than MPG's on your car. With your Rix, you were running at peak speed with a lot of losses so you were a lot less efficient, but if you are looking at true efficiency of the pump the name of the game is minimize losses, then find out where the power/heat/cfm balance out."
Hi Tbone, once again you are thinking on a different wave length than I am. My idea of efficiency is having my compressor work the way the manufacturer designed it to work. I know you probably have some complicated formula but MY FORMULA is real simple... Filling my scuba tanks as fast as my compressor is designed for is the most efficient use of my time... My time spent filling tanks and my time spent diving. That's what peak efficiency means to me.
I hope i haven't offended you by saying this. But I think sometimes you might intimidate people from contributing to the discussion because you get overly technical and maybe too theoretical. I have no trouble understanding Jim Shelden's or AntiqueDiver Bill's explanations. They are literally GIANTs in the field of compressors compared to the rest of us. But I have never seen them go into theoretical territory the way you do.
Again, I mean you no offense. But when I read your comment above, I went downstairs and used my RIX SA3 to fill a set of Twin 48s, another set of Twin 38s, and even a single 50... All from about 500 psi each... And all in 1 hour and 3 minutes. That little RIX is working perfectly and I have absolutely ZERO interest in slowing it down to satisfy some theoretical efficiency formula.