Rotovap Joint Sealing

Anyone have any good tips or tricks to fixing leaks on clamp together rotovap joints? I hate the damn things and I can never get them to seal for shit. Usually I can get them to only leak a little after fucking around with one for like 15 minutes but it’s getting old and I’m pretty sure the leaks are causing vapor carry through and putting more load on my cold traps which I don’t like.

I mentioned to @EffisonAndy that I would kill for a PTFE KF style centering ring sized for common roto joints so I could just use an o ring instead of the stupid flat PTFE washers they all seem to use.

Side note: I’d rather die than have ground glass joints on my rotovaps lol

Which joints leaking? I have a few tricks.

Every one of these types lol:

The ones between condensers and bump trap tend to be the worst

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you using vacuum grease on there? I find that helps.

I like your approach though. @TwistedStill is a machinist and might be able to implement it if you don’t have the tooling. @Soxhlet might also get it solved.

PTFE centering rings and a viton o-ring sounds about right.


I did initially use grease but it didn’t seem help substantially. Admittedly that was when I only had one machine so I should probably revisit it.

If I ever get back to the state where our machine shop lives I could probably whip something up although I will say I hate PTFE on a lathe. I would certainly throw a bunch of money at any of these very competent gentlemen if they did end up making them.

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try a screw gun and a leatherman :rofl:

(I’ve actually threatened to use a rotovap to turn PTFE)


So your looking for a PTFE washer with centering rings so it finds its home easily?

I’ve recently been demoted for opening my mouth and speaking the truth. I have all day long to fit side projects in now…


PTFE tape, common white plumbers style, found in any hardware store- a small liner of the stuff- can be very helpful to seal the inaccuracies inherent in China

Grease should be applied to the outer edges as a stop-gap and not hanging out in vapor path IMO- it always ends up contaminating product and I abhor the stuff


Make sure to tighten your clamps on these like a drum- balance the screws well- do you know how to tune a drum?


Ideally it’d just be a centering ring to hold a viton I ring centered in one of those 60mm ID or 40mm ID joints. Just like a KF vacuum fitting but sized for standard size rotovap joints. I suppose a stainless ring would probably work fine too, I just normally don’t like intentionally putting glass and steel together

Edit: One of these doohickeys:


don’t you hate that?


I agree with the grease sentiment generally. Usually it’s pretty easy to see if it’s starting to run so maybe I’ll give it another shot. I go through like 10 rolls of PTFE tape a week, maybe a wrap around the washer would give it a little more cushion.

I don’t know about drums other than the kind on your pickup truck but I imagine that the premise is the same as with head bolts


Wrap that with shit tape

That was my first thought, but a log of tape a week is a shit load already…

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Ai has viton centering rings for 60 to 100 a pop.


Sorry for late reply. @SidViscous
It was our National Day holiday. Just backed to work.
Now we are using the O-ring coverd with PTFE. Here is the pic.
As I know most of the leaks are due to improper installation after we use this kind O-ring.


Awesome! I’ll DM you shortly about ordering some to try out

Ok, I need the sizes.


Thanks at everybody!!

Glad to know the right solution IS available.

@usalab @ChangMinXD @goldleaf_scientific @LabSociety these need to be available everywhere!!


Figured I’d circle back and update everyone, these seals are great! @EffisonAndy was very easy to work with and got our seals in promptly.

The stock o rings that come with them (FEP covered silicone) are a bit too stiff to seal well but still work about the same as the flat PTFE style ones. Once I switched them to 75 duro viton though we were off to the races. Here’s a video


Anyone ever have the BF nut leaking? That’s what I’m getting right now. And the mother fucker is full of liquid… go figure

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Oh yeah, all the time. Worst thing is rotovapping halocarbons that are denser than water lol. Do you have enough water supporting the flask? It normally happens when there’s too much weight on the ball before vacuum is pulled