itsafineday
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Glassware safety with 22.5 micron vacuum pump
I bought a 2 stage vacuum pump from harbor freight and it will pull down to 22.5 microns hg .
How much vacuum is safe to apply to glassware like rbf , rbf with flat bottom , cold trap and erlenmeyer flask?
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Sulaiman
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There is negligible difference between 1mm Hg pressure and a perfect vacuum - in terms of stress on glassware.
CAUTION : Hobby Chemist, not Professional or even Amateur
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unionised
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I'd think twice about using anything with a flat bottom,
apart from a filter flask which is designed to stand the load.
Incidentally, you can't have a round bottomed flask with a flat bottom.
You can have one of these.
https://en.wikipedia.org/wiki/Florence_flask
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itsafineday
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Thanks Sulaiman and unionised .
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Sulaiman
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This is a useful resource for b.p. vs. pressure
https://www.sigmaaldrich.com/chemistry/solvents/learning-cen...
I bought my cheap hvac dual-stage rotary four years ago and I've not yet used its vacuum capability because;
. the only high b.p. liquids that I've used were mercury and conc. sulphuric acid, neither of which I want in my pump
. common solvents need cryogenic condensers at full vacuum
. I've been lazy and not set up a workable pressure regulation system
. I have no instrument to measure lower pressures, only a plan
. my little 12Vdc vacuum pump is good enough for most things that I do, mostly filtration and rarely (twice) a reduced pressure simple distillation.
So, the most expensive single item that I bought for my chemistry hobby has spent most of its time in its box 
CAUTION : Hobby Chemist, not Professional or even Amateur
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Pumukli
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Flat surfaces and vacuum are not a friendly combo as I heard. I'd never put a flat bottom anything to strong vacuum.
And it includes filter flasks too! My uncertainty arises from the fact that I have a 500 ml filter flask which explicitely states that "Vacuum >
0.3 bar" - which is not a hefty vacuum at all!
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Sulaiman
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I filter at 0.2 to 0.3 bar, depending on the condition of my little vacuum pump on the day,
lower pressures cause solvents to boil and/or froth.
CAUTION : Hobby Chemist, not Professional or even Amateur
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Mateo_swe
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Are you sure the common rb flasks with a small flat surface on the bottom cant be used with vacuum?
With vacuum i mean low enough preassure to boil off solvents and most vacuum destillations.
It seem strange to me that there isnt a warning or a vacuum pressure limit specified on the salesite if there is a high risk of the flask imploding.
I would think many people use these flasks with common vacuum destillations.
I have read somewhere that only round flasks should be used with vacuum but isnt that very old info and not for modern flasks?
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G-Coupled
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I don't think it's to do with 'old' vs 'modern' glassware, and more to do with physics.
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S.C. Wack
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Quote: Originally posted by Mateo_swe  | Are you sure the common rb flasks with a small flat surface on the bottom cant be used with vacuum?
With vacuum i mean low enough preassure to boil off solvents and most vacuum destillations.
It seem strange to me that there isnt a warning or a vacuum pressure limit specified on the salesite if there is a high risk of the flask imploding.
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Are you talking about glass made by amateurs, for amateurs? Are you talking about thin or thick glass? Are you talking about glass that is not heated?
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Herr Haber
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And the sphere is of course the best possible shape 
That doesnt mean a flat bottom flask will necessarily implode. It's just more likely.
That said Deschem glassware is thicker than my Duran Schott, Simex etc. I used it several times for distillations.
At the moment I have two hotplates and no mantle but with a mantle I'd use round bottom flasks.
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
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happyfooddance
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I use 500ml flat bottom "round bottom" boiling flasks all the time, they are great as recieving flasks (can set them on workbench easily), but also
great as boiling flasks (heat better on hotplates). I have used them under vacuum countless times without incident.
I would probably not go any bigger than 500 ml though.
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Texium
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Thread Moved
29-11-2023 at 12:01 |
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