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Author: Subject: How to clamp large flasks?
Fyndium
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[*] posted on 27-1-2021 at 02:04
How to clamp large flasks?


I realized that when going into larger flasks (4L, 6L, 10L, etc), the weight of them gets very large, and I was getting worried is it safe to clamp them from their neck as usual? The vessel should be free to be immersed in a jack lifted heating bath, so underneath support is not compatible. The bath will of course displace the volume weight of water(or much denser CaCl2 solution), as much as halving the weight, but upon adjusting it will be supported only by its neck.
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Sulaiman
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[*] posted on 27-1-2021 at 02:49


based only on experience with my 2L and 5L RBFs ;

the neck will support the weight of the RBF full of water

if the RBF is nearly empty, and 1/2 submerged in water, there will be an UPWARDS force of over 2kg / 20N
so your clamps and stands need to be able to handle upwards as well as downwards forces

unlike smaller RBFs (eg 500ml) you commonly need to siphon liquids in to or out of the flask, (e.g. 10mm dia. glass tube plus pvc tubing)

if possible use a heating mantle for support of the flask.




CAUTION : Hobby Chemist, not Professional or even Amateur
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macckone
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[*] posted on 27-1-2021 at 02:51


The flask itself is probably going to be fine up to at least 22L.
I lift 6 gal (about 22.7L) carboys by the neck when empty.

A better question is the flask + the weight of the contents.

Carboys at least are prone to breakage if you try lifting them by the neck when full of liquid.
A 12L is probably fine if half full, assuming water that is 6KG.
While a 22L full is 22KG, almost 4 times the weight.
A gallon jug full (3.7L and KG) is fine and often have a finger loop for lifting.

Short answer is a half full 12L is likely going to be ok. Keeping in mind not all glass is equal.
Going larger or more liquid could be a problem.
When you get into 50L flasks, they are often jacketed with drain valves and not intended to be moved much.
Anything larger than 12L is getting out side of 'amateur' territory.
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Fyndium
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[*] posted on 27-1-2021 at 04:30


I would think that since flasks are ran generally half full, 5L flask would have approx 2.5kg of net weight, which appears to be ok for clamp. More weight would be added from condensers, dropping funnels, etc apparatus, overhead stirrer luckily weights zero. If the mounts are permanent on the hood structure, they will support pretty much any weight the steel structure can hold in any direction, so buoyancy wouldn't be an issue - though I almost had a mishap with such even when using toy'ish stands, which are prone to tilting anyways. The entire setup takes some time to adjust to it's place, so I've actually used the siphon transfer method for a few occasions with this setup. Another bonus is if several runs are needed, it is immediately ready for new run.

I think even 10 liter is a pretty huge for amateur. Any reasonably scaled reaction would result in huge batches for that size. I use larger flasks only for reactions that require huge solvent volumes, I like to do pretty much everything with smaller flasks, for example all distillations, especially vacuum I do usually in 1L scale max and add more with dropper if needed. Small reaction volume - small mess. Big reaction volume + scaling issues...
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draculic acid69
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[*] posted on 2-2-2021 at 04:36


I'm just suggesting here but I think above 5liters is the point that you need to start
thinking about supporting from the bottom rather than the top.tripods/mantles etc
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catlady101
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[*] posted on 30-3-2021 at 13:00


you can buy these from any science equipment supplier - I would think,it will help in the support of your larger flask, if you can find one large enough or know someone who could make one for you - I think I saw someone here who had their own forge..

https://www.thomassci.com/Equipment/Clamps-Supports/_/PVC-Co...




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Fyndium
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[*] posted on 31-3-2021 at 03:44


Thank god to VPN for circumventing the great european gdpr firewall.

Anyway, those supports for funnels and flasks are not suitable because the flask bottom is to be immersed in a bath vessel. Only way would be to provide some sort of spherical support that encircles the flask, or build a basket or sort of hanger that would be immersed with the flask, but this would be an option for a lot larger vessels, perhaps from 10-20 liters and above. The metal parts should be coated with some soft material to prevent glass-metal contact which can scratch and break glass.

I solved the problem mostly by supporting the flask from all necks, as all my flasks are 3 necked. This also provides a lot more rigidity.

[Edited on 31-3-2021 by Fyndium]
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