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Hi all,

I just thought I'd add this about tank painting. Some friends and I recently
bought 
some tanks from a dive shop going out of business.

The tanks were aluminum 80's made by Kidde (not Luxfer). They are nice tanks
but the 
paint jobs were not as good as Luxfer's. Most of the paint was flaking off and
had 
blisters underneath from oxidation. Since these were aluminum, the oxidation
was self 
limiting and was not a problem.

Except for under the valves, that is. When we had the tanks VIP'd (remove the
valve, 
visually inspect tank, replace neck O-ring, replace valve), many of the tanks
began 
to leak around the necks. The leaks were not real bad, the tanks would lose
about 200 
psi per week, but it was annoying.

We tried replacing the neck O-rings, and tightening the valves but some of the
tanks 
still had neck leaks.

After much hair pulling I finally found that the oxidation under the paint that
is 
under the valve took up just enough space that the valve was not compressing
the 
O-ring sufficiently. We rejected that idea at first because we thought that
such a 
small difference, not really even discernable to the eye, could make that much 
difference.

After loosening the valves, peeling the paint off underneath with a razor
blade, 
brushing the paint flakes and oxidation away, and reseating the valves, the
leaks 
stopped.

I don't know if Luxfer or other tanks will have this problem (the Kidde tanks
don't 
really have a neck, its more of a flat spot on top where the valve is seated),
but 
it is probably worth masking off the area under the valve if you repaint so you
don't 
end up with leaks. The tolerances are pretty tight in that area.

Rick Fincher
rnf@sp*.tb*.co*

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