No vacum leaks to leaking next day

Ok I’m new here and new to distillation. I ran a second pass on Friday and my system was at 300 microns. Started a new run the next day and would not go past 1800. I isolated the pump and cold trap and that wasn’t the problem so the problem is at the connection to the head and boiling flask. I rebuilt the whole thing 4 times heavy grease light grease and no seal. My frustration is that it ran the day before no problem. Any suggestions would. Be appreciated. Side note I bought a used Edwards E2m28 and it’s under warranty but only pulls 350 microns. Any idea on trouble shooting before I send it back? Thanks

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Are you sure its not the receiving flasks on the cow? Have you attempted to helium test for leaks? How about the clamping pressure on your apperatus? Is anything “hanging” that would cause the joint to yaw in it’s cone?
You might ditch the grease, all that stuff is good for is contaminating your product, use a blob of
warm thc distillate and one of these to seal your joints.
You dont happen to have one of those naked probes that I see everyone has going through a thermometer adapter do you? That could be leak #1 !

Have you done an oil change?

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I know that the connection to the boiling flask was leaking because I see it bubbling as material hits it and it sucks in grease that I had to keep cleaning up. Not to say it can’t be leaking anywhere else but I know that is the major leak. I ran it to 160c thinking it maybe vapors and I could see bubbles at the boiling flask connections. I’ll try the sleeves that looks like it would make a better seal. The thing that gets me is that it didn’t leak the day before or was so small it ran at 300-250 microns. I bought the Edwards to try and get below 100 microns. I did add new oil because it was shipped empty. Should I run it and change the oil? I’m really new to the short path so I’m still learning about all the components and pumps used. Thank you for the suggestions!

are you compairing 2 empty apperatus? Or the one you filled vs the empty one? Once full with product the ultimate vacuum is determined really by the vapor pressure of the evaporating/distilling compounds. You will not see the vacuum improve untill you’ve made it past the heads.
Check for leaks in the reviever, you won’t see them untill they bubble like the boiling flask joint did. Helium gas is a good way to test for this.
Whats your cold trap situation like? the better you can protrct the pump, the better your results will be.

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I did run it at 1800 microns through heads but the vacum never went deeper so I shut it down after a half hour to not degrade. I had to run at 218c to get through the heads and my understanding is that at that heat I will get a lot of degradation. I was comparing the vac on the same system. The day before was a 2nd pass and the leaky day was a first pass. It appears my cold trap is working well but how do I really know? I will try the helium but how do I do that? Thanks again.

where did you measure this from? if this was the head thermometer temp thats way too hot. Heads stop around 155-165*c head temp for me.

Is the oil stinky?
thats a good hint.

Blow helium gas around the joints and watch the vacuum guage, helium gas is very small and goes through gaps that air would normally diffuse through at a faster rate.
If there is a leak you will see the guage dip in vacuum.
When you blow the gas around the joints a foil dam can be made to envelope the joint in He.


what kind of grease are you using? The Dow grease can be quite frustrating to use because it’s not made for the amount of heat needed to boil your flask. Use grease made for temperatures at around 400c should stop the leak if it still leaks after that you have a bad joint on something. It’s a lot more money so I use it only at the boiling flask connections and use the Dow for the cow…

That temp was in the boiling flask. I don’t have a thermometer in the head. Yes the oil has a slight smell but not much at all. I have the cold trap filled with dry ice and alcohol and a pan under the ball with the same. What can I do to improve the cold trap? I’ll try the helium and I just ordered the sleeves. Your advice is much appreciated!

I’ll check the grease type when I go in and order better grease if im using lower temp grease. I ordered the PTFE sleeve as well.

You need a thermometer in the head of the apperatus as well, thats how you can tell what is distilling across.

Have you flushed the oil on the Edwards? I do a full flush of several full changes in between passes and after runs. You’d be surprised the effect a small amount of volatile contamination can have on vac depth.

How are you checking the vac on the pump? Thermocouple gauge on the inlet?

As far as your system, you clearly have a significant leak. Are you running wide bore or gl connections? I run gls on a cheap AI pump and I routinely get into the mid 30u range during my main on the second pass, so deeper vac levels are possible. My advice would be that if you’ve fixed a problem several times and it’s still not fixed you probably have other problems. Look for other culprits like leaky hose clamps, loose gls, crushed orings on thermocouple adapters, etc… if I have a leak I can’t find I assume everything is leaking until I prove otherwise.

Also, I know you said you isolated the cold trap but 9 times out of 10 my cold trap is what’s leaking.