Rotary Evaporator Troubleshoot

Hey everyone,

I hope someone can help me identify the issue. I’ve spent the entire day taking my 50L Rotary Evaporator apart and I can’t locate the issue.

It seems that the system is struggling to maintain a vacuum. The odd part is that it can hold a vacuum (around 0.095 MPa) as long as the boiling flask is oriented a certain way. If I rotate it 180°, there is an audible leak and pressure quickly increases back to atmospheric pressure.

Does anyone have any suggestions? I took out all the gaskets, changed them, greased everything, and the problem persists.

What direction does it hold vac?
The problem is somewhere in your rotery seal.
Ps: Dont use grease in a rotovap rotery seal, the etoh might not dissolve it, but other solvent like hexanes will eat it. Thats product contamination just waiting to happen.

I had mine leak at the condenser and motor. Took me 45 mins to figure it out.

Reposition, retighten, recheck


The point at which I insert the rod from tightening is when it holds vac. 180° after that is the leak.

You sure it’s not the seal between the evaporating flask and motor? If you leave that overnight with product inside the weight will warp the seals and cause such a leak.


I’ve changed it out with different gaskets (in exception of one) and was unable to fix the issue. It may be that single gasket and will be the next thing I replace.

This can also be caused by a defective vapor tube which I observed with smaller units. If the vapor tube is not 100% straight it can warp the gaskets while at certain rotational positions while working fine in others. I had this problem when buying replacement parts from Ace but with ones from the original manufacturer it worked fine.

I second @goldleaf_scientific , check the seals near the motor, try helium testing.

I know the location of the leak. I am having issues locating specifically what is causing the leak.

Try cleaning between the grey gasket and the gasket inside.