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At 20:32 20.04.98 -0700, you wrote: > > > Okay, I know there is a huge amount of hype over "Oxygen clean and >compatible." I knwo that if you are getting partial-pressure blends, it is >a good idea to have your tanks O2 serviced. My question now is about >regulators. For EAN that is 40% or less, what should I REALLY be doing? >Do I need new o-rings in all of my lines? Do my 1st and 2nd stage need to >be serviced? > I seem to get a different answer from everyone I talk to, ranging from > >"Our equipment should never be used with EAN, best get our new green-body, >dedicated Nitrox regulator that is good up to 21% Oxygen" > >to > >"I use whatever regulator I want for my 100% O2." > >For basic Nitrox work, what should I do? I was looking to buy a new reg >soon, either a Sherwood Oasis or one of the Scubapro G-series. Are either >of these going to be a problem? Thanks, > > > >John Norman >arclight@ex*.co* The general rule is air standard up to 40% and oxygen clean and compatible beyond 40%. Thus, a special ultra-clean dedicated reg for bottom mix is not needed; there's no point to buying a nitrox version. Further, most (possibly all) regs will function just fine with 100%. Theoretically, standard lubes in the first stage may cause an explosion but the practical problems are more likely long-term compatibility. You may find that O-rings and plastics deteriorate a lot faster. I've used nitrile O-rings and changed them every 6 months since they got brittle. All experience indicates things rot rather than going bang in a big way. The first stage regulator is the main concern due to high pressure. There is much less need to worry about the low pressure hoses and second stage. My advice: Use any reg for nitrox up to 40%. Further, dedicate oxygen regs for long-term use, either by servicing them at frequent intervals or by switching to fully oxygen-compatible parts. Use Christolube or equivalent. If you need a reg for a high-oxygen mix once in a blue moon I would not hesitate to use any ordinary reg. However, I would expect to see accelerated deterioration of O-rings, diaphragms and plastic seatings. The rule for partial pressure filling is similar: Oxygen clean for anything that sees more than 100% at high pressure. Again the "off the record" advice will be: worry more about stage cylinders that may receive 3000 psi of pure oxygen. The amount of oxygen needed to make a 32% or a 40% mix is a much lesser concern. As long as it's filled slowly oxygen first we're talking 750 psi of oxygen max. In the latter case I wouldn't worry too much about an occasional single-filtered air fill provided the cylinder valve was lubricated with a non-flammable lube in the first place. (If you fill air of a quality poor enough to cause explosions you'd better not breathe it anyway). Avoid heat (fast filling) and adiabatic compression (shocking the gas by closing a valve fast). If it's all rocket science clean anything may pass but in practice it's a lot easier to ensure safe handling by going gentle. It's amazing what burns in pure oxygen if you do it all wrong -- and, it's reassuring what works if you avoid shock filling and heat. (Quarter turn "quick" valves have probably caused more oxygen explosion than anything else. The recipe for disaster is, establish a violent flow rate and block it in a split-second by turning the handle 90 degrees). Conclusion: Oxygen will make incompatible materials deteriorate; it hardly ever causes explosions unless you do something way stupid. It still makes sense to strive for high compatibility to avoid failure. At the risk of sounding careless, I think we should focus more on long-term performance in oxygen service rather than worrying about explosions. As divers realize the explosion hazard is exaggerated they may think it's all bogus. In reality, it's more a question of how long components will last. Unless you are willing to accept frequent service intervals the conclusion stays the same -- go fully oxygen compatible at high oxygen pressures. regards, Hans -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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