AI 20L Rotavap Flask Positioner Issues - Cracking Boiling Flask

Purchased a brand new AI Rotavap last year and in less that 6mo of use I’ve had to replace the white PTFE “flask positioner” 5 times due to dents that get created when it gets tightened. If you don’t tighten it, you don’t get a seal, if you do tighten it you dent your positioner and have to replace it, if you don’t replace it and you have to tighten too tight and it will crack the lip of your $350 flask. Their customer service is great at reading the scripts and giving inequitable solutions.

Now I see why these things are constantly listed for sale by different labs. I accepted the flask positioner just as an expensive consumable item, but now seeing it can crack the lip of the flask, I can’t accept that cost 2-3x a year.

Am I just experiencing what a typical AI customer experiences?

I know a lot of variations of these units are on the market, anyone experience something similar or have a fix for their cheap engineering?

I ran into the same issue with mine as well. Eventually I just dealt with it. After spending thousands in pyre gasket sets, I said the he’ll with it and dealt with it.


Post a pic, i can make you a viton gasket if i can get dims or a sample.

I have compressible PTFE material as well, been playing with a lot of custom sealing solutions as part of R&D for these LLX columns

It would be fun to come up with a solution for you and list it on the site when we launch next week

Can you provide a link to the problem part?

Edit: found it

Its the white bit that is problematic? That looks super simple- how hot do you run the roto and what solvents do you use?


200% Ethanol Solvent for BHO winterization.

Ran between 40-50C, 30-50 RPMS, 30-40hr. a week operation. Typical vacuum is -25 to -28hg

Can you weigh the part for me?

That would be awesome! It is the white piece.

I will happily buy a new one and send you a dented one.

I know it’s an ongoing an issue, probably the same reason they started tracking consumables for their machines, specifically this part.

Heidolph did have a superior part that connected the flask and the only maintenance for it was doing an ethanol soak at the end of the week. I’m unsure what it was made of.

They charge me $60 for this part and it looks like it’s a 4-5 week part that needs to be replaced or it compromises the flasks integrity.

I weighed three different ones- 19.79g, 19.70g, and 20.38g

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Ok, shoot me an email
And we can exchange info there

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Got to get a sample to make a mold off of but i can make a 5 pack of these for you for ~$150

E-mail sent!

won’t viton be missing the required slickeryness to make this particular seal work?

the lubricity of the ptfe seems critical to rotating the nut with relation to the flask.

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Good point, i have pc/ptfe filament on hand and a high temp printer that is supposed to have been delivered today but looks like next week- im wondering if some part can be made to be compressible so they become less of a ware item

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envelope gasket style would not seem inappropriate.

springy and slickery in the same slice.

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I don’t tighten mine down too hard. If vacuum is good one shouldn’t have to tighten to the point of ruining seals and/or cracking glass. A solution seems needed though for this particular system.