excellent post, Hans

-----Original Message-----
From: Hans Petter Roverud [mailto:proverud@on*.no*]
Sent: Thursday, October 26, 2000 8:24 PM
To: Duane Liptak Jr; techdiver@aquanaut.com
Subject: Re: oxygen cleaning


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

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