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Author: Subject: Glassware safety with 22.5 micron vacuum pump
itsafineday
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[*] posted on 17-1-2019 at 10:07
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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[*] posted on 17-1-2019 at 12:37


There is negligible difference between 1mm Hg pressure and a perfect vacuum - in terms of stress on glassware.




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[*] posted on 17-1-2019 at 12:42


Quote: Originally posted by itsafineday  

... rbf with flat bottom... erlenmeyer flask?
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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[*] posted on 17-1-2019 at 16:12


Thanks Sulaiman and unionised .
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Sulaiman
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[*] posted on 17-1-2019 at 17:37


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 :(




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Pumukli
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[*] posted on 18-1-2019 at 05:33


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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[*] posted on 18-1-2019 at 06:50


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.




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