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Re: Gas in the Lines
Posted By: Don Miner In Response To: Re: Gas in the Lines (SVP Neon Equipment)
Date: Thursday, 25 October 2007, at 10:27 p.m.
> I have never understood why most mfgs. use a
> copper line as a gas reservoir between the
> canister and metering valve. When the line
> is "filled up" from the canister
> it has the same pressure in it that the
> canister has. With this arrangement there
> are a lot more connections and therefore a
> lot better chance for a leak. You also have
> the problem of contamination from the copper
> line. If the copper were OFC grade (oxygen
> free copper) it would help. But it isn't. It
> is just hardware store grade, which has the
> potential to oxidize internally over time
> and contaminate the gas stored in the line.> With a system like that it is essential to
> heat the copper line a few times to a high
> heat while it is under hard vacuum to degas
> the metal as much as possible, much in the
> same way that an electrode is degassed.
> Otherwise, whatever gas is stored in the
> line may become contaminated. Some claim
> they do not do this procedure and have no
> problems. This brings up the question of
> what they consider "no problems"?
> If a red unit does not come on red and stay
> red while running on 2 to 3 times the normal
> operating current, there is a problem.
> Putting research grade gas (99.9999% pure)
> into a hardware store grade copper line that
> has not been washed out and has not been
> high temperature degassed will reduce the
> purity of the gas without question. The
> longer the gas stays in that line, the
> greater chance there is for contamination.
> Even with a stainless steel line, it should
> still be washed and degassed before using it
> as a reservoir for pure gas.> Mark
True enough Mark, My manifold is all glass, I still use the glass flasks, guess this oldtimer's habits will die hard. Maybe some day I will 'Bite the Bullet' and get one of your 'New Fangled' pyrex jobs. Cheers, Don
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