VacSeal question

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
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Bob_Palmer
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VacSeal question

Post by Bob_Palmer » Fri Nov 18, 2005 10:28 am

I have an application where I am expereincing a vacuum leak on a viton seal between a loadlock and a gate valve manifold. My loadlock achieves -6 milibar but should get in to the low 7's. When squirting the crease between the loadlock and manifold the pressure rises from 1e-6 to 3 e-6. The gatevalve and airlock manifods are rectangular and the viton oring sits in a rectangular groove on the gate valve manifold. My problem is tthat he dissasembly and repair of this leak is extremely labor intensive and rife with peril. Is VacSeal a viable solution. It seems to me that the VacSeal would have trouble migrating from the crease between the manifolds to the groove where the oring sits. I am also concerned about outgassing, this loadlock has internal baking and can achieve 150degrees C so I guess curing can be done more quickly. Any thoughts are appreciated. Thanks in advance. I sent a word doc attachment showing a picture of the gate valve.
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DaveC
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Re: VacSeal question

Post by DaveC » Sat Nov 19, 2005 12:43 am

Bob -

I am having difficulty forming a mental picture of the exact geometry you are describing, and where the leak seems to be. The pressures are actually pretty low, for O ring and elastomer parts. Viton will outgas at these pressures for up to 24 hrs following an exposure to atmospheric conditions.

Couple questions: The pressures are in Torr (mmHg), yes?

a) For leak detection - are you using a He leak detector or volatile liquid? My first reaction was that you have a porosity in the viton seal structure. But... a fine porosity and a liquid leak checking routine, usually experiences a vacuum improvement first, as the liquid seals the porosity, then a pressure rise as it evaporates into the chamber.

2. Are the Viton O ring seals and/or the grooves perfectly clean and unblemished? (Can you use a light wipe of HiVac greas.?)

3. Vac Seal is probably... ( a bit uncertain in my mind) good up to 150 C if you can live with the initial outgassing. There will be some, but it should diminish fairly quickly as the material thickens.

4. Can you be sure that no weld areas are suspect? I once had a hi vac leak valve with its own non-controllable leak...through the valve body casting. We used the GE vac seal stuff. to seal it. It DID work... but the valve was a sticky mess.

Dave Cooper

At any rate, it should be considered a desperation, short term leak fix. Good for getting you up and running... for a while, but possibly a bit iffy as longterm solution.

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