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Re: Gas in the Lines
Posted By: SVP Neon Equipment In Response To: Gas in the Lines (Dana)
Date: Thursday, 25 October 2007, at 12:18 p.m.
> The gas that sits in the tubing between my
> canister(s) and the manifold valve is a
> minimal amount but there is always some left
> inside-under pressure of course.> If there is a space of time between
> bombardings, which happens quite frequently,
> I am concerned this 'leftover' bit of gas
> may not be as pure anymore.> Many times I have dumped the gas to allow
> the entire tube to be outgassed to the tank
> valve, then ladled more gas. I think I am
> wasting gas.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
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