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At 09:33 PM 10/23/00 -0400, Duane Liptak Jr wrote: >1. What exactly needs to be done to a regulator to make it safe for >mixtures of 40% to 100%? (Beyond the tear it down and clean everything with >simple green, trichloroethane, or other solvent part.) Beyond basic cleaning, nothing. > a. Does every O-ring need to be viton, just high pressure side, or are >nitrile/butyl o-rings acceptable? I know that many aviation applications >use nitrile, but viton seems to be mandated for scuba uses. What's the >deal? Viton is better in theory but nitrile lasts longer. The nitrile deteriorates slowly with prolonged exposure to high PO2 -- it does not cause flashing. Next time you service the reg you'll replace the O-rings anyway. > b. What needs to be done with hoses, especially HP? ( clean them, use >new hoses rated for O2 service, etc.) Use new hoses > c. SPG's: Should they be cleaned, and how? Do the spool O-rings need >to be changed? Use a new SPG. There's no practical way to clean the Bourdon tube. > d. Second stages: Do the O-ring, diaphragm, and seat materials matter >at the lower pressures that this system is exposed to? How about lube? In practice, no. Lube should be oxygen-compatible but intermediate pressure is not a problem. > e. Are Sherwood regs (with the rubber dry air bleed valve) acceptable >for use with high FO2's? (academic question--I use Zeagles) A slow, constant bleed should be OK >2. Tank valves: Do quick opening valves, like some Genesis K's with coarse >threads on the seat, pose a danger with high FO2's? Here comes the real culprit -- quick opening valves. If you want to provoke flashing use a quarter turn valve. They're involved in the majority of accidents involving high-pressure oxygen. We tend to focus a lot on cleaning and less on how we handle the gas. The recipe for disaster is anything that shocks the flow of gas, sudden opening of valves, restrictions and sharp turns. Almost anything may burn in pure oxygen, provided you "abuse" the flow of gas. Conversely, almost nothing will catch fire if you go gentle. The sudden opening and closing of valves is the problem. If you avoid mistreating the gas you're basically left with the issue of slowly deteriorating incompatible materials rather than an overt risk of flashing. Use needle valves and open them slowly. Any valve that suddenly goes from 0 to full throttle in one second is NOT an oxygen valve. Once the system is pressurized the risk of anything going bad is minuscule. As cleaning is concerned, focus on the high-pressure end of the system. 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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