tekkado - 28-6-2017 at 13:09
Hi Guys,
I've been reading various threads about different vacuum pumps and reading about performing vacuum distillations.
The pumps available on eBay such as this one:
http://www.ebay.com.au/itm/6CFM-1-Stage-Refrigerant-Vacuum-P...
All seem to pull 15 microns total vacuum and the CFM is the flow rate, correct that changes?
I've read some comments of users pulling 3mmHg with such a vacuum as above. This sounds too good to be true? Or is it just the beauty of Chinese
manufacturing now a days?
Also applying a vacuum and boiling water at room temperature for example, is this considered a major vacuum on glassware? The guides I have read
detail the set up and practical use of vacuums but no mention of safety?
Yet on here, have read accounts of glassware imploding. Are there any guidelines for carrying out vacuum distillations safely at higher vacuums?
Thanks,
Tek
JJay - 28-6-2017 at 13:52
My vacuum pump has similar ratings and can pull a 2 mm Hg vacuum with no problems. It's not Chinese (it bears a sticker saying it was "designed in the
USA," but I guess it was probably manufactured in Mexico), but it was less than half the price of that vacuum pump.
In general, you should not use flasks under vacuum unless they are round bottom flasks or are designed for use under a vacuum, although you probably
won't have any problems. Don't use cracked flasks under vacuum. You don't need special glassware for "higher vacuums," but you do need glassware that
can be safely used under vacuum.
tekkado - 28-6-2017 at 15:23
Yeah they all seem so similar and just trying to wrap my head around how capable they are. I think i confused myself reading through the fridge pump
sticky, applying that info to these pumps but they were talking about compressors.
Would using step down/up adapters between glassware joints be a no no?
JJay - 28-6-2017 at 16:47
I hardly ever use those, but I think that would probably be fine.
[Edited on 29-6-2017 by JJay]
Melgar - 29-6-2017 at 01:30
A good rule of thumb is that flasks less than a liter (or a liter or less for RBFs or flat-bottom rounds) can withstand a full vacuum as long as they
aren't defective. Above that, you have to be more careful.