OK, thanks. I got a laugh from that. Compressing NITROX puts no unusual strain on a compressor excepting the oiless type. The dry sump compressors like RIX don't like compressing a clean gas as water from the atmosphere constitutes a lubricating agent but they will do it with a slight heat penalty. This has no effect on compressors which have an oil sump. There is no "oxygen compatible" lubricant excepting the $600/quart stuff made by Dow Chemical. It is a fluorinated hydrocarbon, a kind of liquid Teflon. All the compressor operator can do is a kind of risk assessment or trade off of benefits and risks. For NITROX and lubricating oils the key is O2 concentration and heat. The combination causes oxidation of the oil and is unavoidable. However, it is relative to the type of oil. Omnilube PAO oil is 2.5 times as resistant to oxidation as any diester that I have heard of which is used in divers' compressors. This conclusion came to me after analyzing the data received over the telephone to various vendors and manufacturers like Ultrachem (they wouldn't answer my Emails except with an occasional platitude and their published data sheets are thin). Oxygen hazards should be weighed against mechanical properties of the oil. Bauer, for example, tests their compressors by running them into the ground. Under these conditions of heat and wear they decided in favor of the very heavy, diester oils like Anderol 455. They do a fairly good job of keeping the valves clean but to me are a little bit creepy. Pthalate esters are viewed with suspicion cancer wise and some Euros have taken action to restrict or control in some products. However, Omnilube PAO oil is possibly safer and though lighter in weight and therefore having a naturally lower flash point, contains advanced additives to control oxidation and wear, etc. It is impressive stuff, especially for a food grade oil. It is not known to be a good solvent and I can't comment on long term scouring action WRT compressor valves. However, the residue which I have seen appears to be soft, not hard as flint like I've seen with some esters. Bottom line is that the jury may declare a mistrial and never come to a firm conclusion. My bet is that PAO's like Omnilube are the way to go.
The only way to know what's "best" is via oil analysis for wear particles, etc. But an oil change only costs a couple dollars so there's little reason to push the limits.
