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Clamps & vacuum
Posted By: SVP Neon Equipment In Response To: Re: Grounding Electrodes (Dana)
Date: Thursday, 31 March 2011, at 3:41 p.m.
> There was no observed stress on the parts
> since I can completely relax the clamping
> assemblies without any change on the seal.
> Transco provides a light duty, 3-screw clamp
> made of acrylic pieces instead of the
> standard KF clamp that would be used on
> metal KF parts.> This provides more than enough pressure on
> the glass faces to maintain a seal in the
> vacuum range we work in.> A normal KF situation of course would
> specify a torqued clamp that would withstand
> high pressure or vacuum ranges that would
> exceed the range we work with.I am asking these questions in hopes that perhaps I may learn something. You have asserted some comments that would indicate you have expertise in this area, so I would like to validate and quantify that expertise before I place any value on it.
When you say there "was no observed stress", what did you use to determine this, or how did you determine it? Did you use a polariscope? If so, did it display a gray/white or full color presentation? What about when the clamp is applied? Is there still no stress? With glass tubing, even the slightest pressure against it (as though you were going to bend it), stress will be observed. The more pressure, the more stress. So I am very interested to know how a clamped glass flange, or for that matter even an unclamped glass flange connection that is under vacuum, will have no observed stress and how you determined this.
If there is no change in the integrity of the seal by relaxing the clamping assembly, why use any type of compression O-ring fitting at all - KF or otherwise? How did you determine there was no change in the flange seal? Did you do a helium leak test, or use some other method? Are you saying an elastomer seal does not require a certain amount of compression to maintain a reliable vacuum tight seal? Or am I reading too much in to what you said? If there was no change in the integrity of the seal without the clamp, you should be able to vent the manifold to ATM and still have the seal remain intact and leak free. How is this possible?
I am aware of the "homemade" plastic clamps Transco uses. Are they not the same ones Eurocom uses? To clarify, when I mentioned using the correct clamp for glass KF flanges I was not referring to the standard metal KF clamps that are used on metal KF flanges. I was referring to a plastic chain-type clamp that is specifically made for glass KF flanges. Considering your comments I assumed you were aware of these. Even using these clamps will still induce stress into the flange, though much more evenly. That is, unless you know something that I don't. If so, please enlighten me.
May I ask what you consider the "vacuum range we work in" to be?
Other than the fact that we are talking about glass instead of metal, why should this not be considered a "normal KF situation"? Should we not try to obtain the most leak-free vacuum system possible in an effort to avoid potential problems? Or are you implying that everything up to this point (relative to neon vacuum systems) has been over engineered and not necessary? Enquiring minds want to know.
Mark
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