Short Path Distillation Problems

Hi there.

I’m working on getting my first successful short path distillation under my belt but I’m running in to issues.

So I’m running an adixen 2021i that goes down to 20 micron blanked off (using a Supco VG640D vacuum gauge).
I’m able to pull 500-600 micron in my short path setup until I get to about 110 celsius. Once I reach that temp my vacuum gauge jumps WAY up to around 4000-5000 micron.
At that time I’m getting alot of smoke (violatiles) running through my cow and the head temp stays around 30 celsius.
I was pulling a bit of terpenes etc. in to my first receiving flask but I ran up to about 230 celsius and never hit cannabinoids. I’m sure it’s due to the vacuum levels having jumped up to 4000-5000 micron at that point.

Does anyone have any idea why when my mantle heats up to 110 celsius +, my vacuum level all the sudden jumps from 600 micron up to 4000+ ?

This is my second failed attempt and it’s happened both times. Definitely beyond frustrated…

Any advice would be greatly appreciated!


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Have you checked for vacuum leaks?

Smoke is usually a sign of oxygen being present


I have not. If there is a vacuum leak I’m wondering why it wouldn’t be apparent at the beginning of the run when I’m able to hit around 500 micron. Wondering why when I hit around 110 celsius I’m all the sudden jumping way up to 4000+ micron.

I feel like if there were a vac leak I would be starting out around 4000+ micron not half way through? Or am I mistaken. Definitely a beginner trying to figure it all out.


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2nd vac leak… If your blanked off goes to 20 then surely 500 isn’t the lowest your spd would reach if it were not leaking. It should easily get down to 300 or below. Try properly greasing then vac down once there spin all your joints and watch vac levels. If your not full bore check those hose ties and clamp em tighter.


Not full bore yet. Would like to move that way once money allows. But thanks will re-check all connections. Do you think the vac leak must just become more apparent as the run goes on? That’s why the vac level is jumping up so much higher half-way through the run?


It’s probably showing the leak more at that temp because stuff is starting to vaporize and fight your vac


I’m not an expert… But the higher you go in temp the more evaporates off your crude therefore effecting your vac reading. More violatiles present = higher vac reading

After your burn off all your initial vapors you’ll notice your vac levels drop


Thanks guys. Will check connections tomorrow, try another run and report back!

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Are you waiting for the oil to end its decarboxylation period? It can take a while before the co2 stops coming off the oil and killing your vacuum level. I would leave it at 135C until it stops bubbling in the flask and the vacuum level drops before raising the temps further.


Im with @2terps_roji this smells like decarb, or it would if i was there


Can you describe how you decarbed the material? Did you decarb in the spd boiling flask? Or decarb prior? What temp did you reach and for how long?

Was this measured inside the crude or on the outside of the boiling flask?

I decarbed in the round bottom flask with a heating mantle at 110 celsius for about an hour before I hooked it up to the short path and ran it.

It was measured inside the crude

If your using gl connections and you tightened to hard that’s likely where your leak is. First time I ran an spd I spent an hour trying to get under 100 micron i was stuck around 500 give or take 100 micron. Take them off and check the plastic/black ring.

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Hmm. I think in theory 1 hour at 110C should be good? But I think many people, myself included, go up to 150C.

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You should go up to 140-150c to degas completely when you decarb. It will remove a massive chunk of what you’re removing in the spd.

Also start using bellows instead of gl connections and hoses. It will make your life easier once you’ve mastered that.

Edit: lol @tetramethylsilane . Great minds think alike and apparently type at the same time.



Yeah definitely upgrade to full bore (kf25 bellows) ASAP. I suffered thru a GL18 2L for half a year before upgrading to a pretty sweet full bore set up and damn does the wider vapor path make a world of a difference. In terms of run time and vac depth.

You can probably upgrade for cheaper than you think too. If you post a pic of your set up, we can get you squared away.

Oh wow that high! Done. I appreciate the decarb info!

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I almost did upgrade but I have this crude so I figured I’d run this through then upgrade for the next batch I make. Here’s a pic of my current setup.