GammaFunction
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Which jointed flasks are safe under vacuum?
I think the following are safe
small to medium (2l?) round bottom, flat bottom round, or pear shaped flasks. Not large RBFs.
any flask with a vacuum outlet.
Any connectors, adapters, or condensers.
What about ground-glass-jointed Erlenmeyer flasks? Is there any size below which they are safe?
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bfesser
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Generally, the better quality labware should all be fine. Chinex is more likely implode. Beware of star cracks and deep scratches. There's plenty
of info on this subject already here, if you're willing to search for it.
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GammaFunction
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I've done some searching for things like "flask vacuum safety" but I can't find too many threads. Some people say that everything is OK up to 22l;
other people say not to trust Chinese glass. Other sites say never to use an normal Erlenmeyer under vacuum.
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[Edited on 7/13/13 by bfesser]
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Lambda-Eyde
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Quote: Originally posted by bfesser  | | Generally, the better quality labware should all be fine. Chinex is more likely implode. Beware of star cracks and deep scratches. There's plenty
of info on this subject already here, if you're willing to search for it. |
I'd never trust a spotless Pyrex® erlenmeyer with a vacuum. It's more a question of geometry than glass quality, really. I think the latter is more
important when heat and/or temperature differentials come into play.
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GammaFunction
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| Quote: Originally posted by Lambda-Eyde |
I'd never trust a spotless Pyrex® erlenmeyer with a vacuum. It's more a question of geometry than glass quality, really. I think the latter is more
important when heat and/or temperature differentials come into play. |
I can see why, given the lack of compressive strength on the flat bottom, but the shape is very convenient.
For example, what would one use with a jointed Buchner funnel?
On this page they use an ordinary Erlenmeyer, but it looks a bit rounder than normal, maybe to address the geometry issue. But the flasks aren't
labeled "safe for use with vacuum."
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gutter_ca
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I've used thick-walled erlenmeyers in a pinch, wrap with ParaFilm in case of implosion.
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BromicAcid
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What's safe? What's not safe? It varies by who you ask. I have heard that flat bottomed flasks like Erlenmeyers are frowned upon simply because the
flat bottom means they are more likely to be sit on something that could chip them or 'tink' the glass when under vacuum thus causing them to rupture.
Many companies actually sell vacuum Erlenmeyers which are simply thick walled Erlenmeyers coated in plastic. Whether this is to protect the flask
from getting chipped or to protect those nearby when the flask gives way is something I am not sure of.
On the other hand we routinely use 20L glass bottles at my work with flat bottoms and they are usually used for filtrate collection and are routinely
pulled under medium (30-60 mm Hg) house vacuum. Again I have been warned to keep them in containers and not sit them on the floor because sitting it
on something hard that could tap the bottom just right might cause it to give way.
In terms of ultimates, and something that is a matter of contention even among people working in the same lab is the use of sintered glass funnels.
Some people will pull vacuum on the receiver only. Others insist they should only be used under pressure with the receiver at atmospheric. Yet
others insist that vacuum on the receiver and pressure on the top is the way to go. And others will call those people crazy. From what I have seen
it all depends on the surface area, a small sintered glass funnel with less frit surface area can take more simultaneous pressure/vacuum before it
gives way (and some eventually do). It makes sense right?
It is quite interesting. I have had people tell me I cannot pull a addition funnel under vacuum on a setup whereas no one complains that a coil
condenser with walls of similar thickness gets pulled under vacuum.
I routinely see 50L, and even 72L flasks pulled under full vacuum (<0.01 mm Hg) without any issues, all sorts of adapters, connectors, even a 100
L. Never have I seen a failure or even heard of one. But I do think some of that is that we always use good glass. I think brand name glass makes a
difference.
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