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Registered Member #509
Joined: Sat Feb 10 2007, 07:02AM
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Posts: 329
Bored Chemist wrote ...
If it's big enough you might want to get thepolycarb jar out of the trashcan and use it as an implosion shield. If the glass belljar breaks it won't be pretty.
It is the trash can ;) and unfortunately its not big enough.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843
Well with it set up as shown it pumped down to a little less than 500 mT, which isn't very good, IMO, but there's a leak at one of the adapters near the pump.
The only thing I had to do was to push down on the acrylic a little bit when it first started pumping, but then it was self sealing after that.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
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Hello C of D,
The only problem now is that my vacuum pump is junk. Actually it's not the pump, per se, but the inlet fitting that came on the pump. I never really looked at it/studied it very closely until now, when I realized there's a leak there somewhere.
It looks like a little kid designed it, or at least someone who doesn't know much about vacuum systems.
The pump is supposed to be capable of going to 15 mtorr, but I can't get it below 200 mtorr...so I either have to try to modify the fitting or make a new one, or possibly just get another pump.
Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
500mTorr is pretty poor- but it should be good enough to degas stuff. If you get the pressure low enough you will boil the potting compound and that won't help.
Registered Member #509
Joined: Sat Feb 10 2007, 07:02AM
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Posts: 329
Bored Chemist wrote ...
500mTorr is pretty poor- but it should be good enough to degas stuff. If you get the pressure low enough you will boil the potting compound and that won't help.
+1 to that, our only goes down to 1 torr or so, but all our tubing is just slip fit connections, plus our gauge is only graduated in torr, not using any vacuum grease, and our valve setup isnt anything fancy. But it works great for what I use it for. After I clean out the inside of the assembly with flux remover, I put whatever assembly in the chamber, run it down to dry it out, and the gauge hangs at ~20 torr for a while while the solvent evaporates. Then again around 8-5 while water evaporates, then down to 1 slowly.
When I'm encapsulating stuff, I pull out potting down to 5 torr or so (it rises, falls, boils for a bit... slows down, but stays expanded some) then I put the potting into the assembly, and pull it down to ~20 torr or so, our potting expands too much below 20 torr, and I'd need a larger reservoir at the mouth of the assembly. Your system should be more then adequate for vacuum potting, even of high voltage stuff. If youre trying to oil impregnate something and you wanna be really sure, heat the object and oil before you put it in.
looks like you wont have to worry about boiling the mineral oil (if youre oil impregnating), unless you get it to ~ 200C
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
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What kind of vacuum pump are you using? Just based on your description of your use of the pump, I'm thinking it may be a dry scroll pump like an Edwards XDS-10? Or is it a common rotary vane pump with gas ballast?
I used to have an old Welch pump and know if I pumped any quantity of anything volatile, it contaminated the oil and became a real PITA.
I can't afford a dry scroll pump right now, so I'm leaning toward buying the Viot pump over the Harbor Freight pump...just because the Viot has the gas ballast feature. Having never had a pump with gas ballast though, I don't know how effective it really is in practice.
Registered Member #509
Joined: Sat Feb 10 2007, 07:02AM
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jpsmith123 wrote ...
What kind of vacuum pump are you using? Just based on your description of your use of the pump, I'm thinking it may be a dry scroll pump like an Edwards XDS-10? Or is it a common rotary vane pump with gas ballast?
I used to have an old Welch pump and know if I pumped any quantity of anything volatile, it contaminated the oil and became a real PITA.
I can't afford a dry scroll pump right now, so I'm leaning toward buying the Viot pump over the Harbor Freight pump...just because the Viot has the gas ballast feature. Having never had a pump with gas ballast though, I don't know how effective it really is in practice.
rotary vane gas ballast pump, you got it Hmm looks like they say its a lot more capable then what we are getting it to, but I suspect the tubing and fittings, and no grease on the seal, are the culpret there. I should probably run it for a while with the gas ballast open to 'freshen up' the oil too.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843
Well I made a new inlet fitting for this "Dosivac" vacuum pump I got from ebay, out of a brass flare fitting, and I attached the thermocouple tube to it, and it pumped right down to about "0" on the meter.
So I guess the pump itself is pretty good...as good or better than my old Welch belt-drive pump.
It's mind-boggling to me that a company could make a pump like that and then compromise the whole design...throw away the performance the customers want and are paying for...by mating the pump to an inlet/valve assy. that can't help but leak.
Anyway, hopefully now I can get back to finishing the coils...
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What's the best off-the-shelf solution for a vacuum encapsulation chamber?
