Question about achieving sub 1000 micron level in short path(vacuum hosing)


Hi so like the topic says I’m on a quest to improve the vacuum level in my short path. With the current set up we typically end up pulling cannabinoids around 215C in the mantle and ~1600 micron vacuum level after the first cold trap. I would like to get down to pulling cannabinoids around 170 - 180C and 50 micron.

Current set up is a 20 L summit boiling flask with one glass cold trap --> then some of this vacuum tube(wall thickness is only 0.11") --> into a 6" steel bhogart cold trap and viton gasket --> connected to Welch CR/V Pro 16 with some red rubber vacuum tubing(not sure but wall thickness appears about 5/16").

When I hook the CR/V Pro 16 straight up to the vacuum gauge through the red rubber hose it pulls about 52 micron. As soon as I hook up the steel cold trap with the thinner walled vacuum tubing the vacuum jumps to about 512.When I hook up the whole system and dry vac it pulls about 600. Seems to me that the vacuum hose or steel cold trap is preventing our system from pulling sub 1000 micron during distillation. Is it possible that the clear tubing listed is not made for these vacuum levels? I have seen that a lot of people run with no rubber tubing and go all metal bellows, what is the advantage of this?


It would be helpful to see a picture of your rig if you have one. What vac grease are you using? How much are you using? What are you making your connections with? GL16s? What are you putting in your cold traps? How are you treating the crude before distillation? What are you using for crude?

Sorry for all the questions. Just trying to hone in.

Quick take-- you got some serious leaks and possibly not enough cooling capacity.

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Will try to get a pic up later but for now.

Vac Grease: Dow Corning High Vacuum grease
Vac Grease Application: A thin layer about 1/3rd down the joint
I I believe the connections from the glass gold traps are GL 18s from summit. The cold traps is a kf 18 barb I think.
Cold traps are filled with dry ice and isopropanol mixture.
Crude is from cryo ethanol extraction at -40, ran through activated carbon filter and then recovered in falling film.


Arent them pumps suppose to get to like .4 microns blanked off? 52 microns sounds a bit high for such a high end pump blanked off. when you use that red vac hose are you using clamps??

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You might form as good if not a better seal with just a little more grease;

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Is your ballast open or closed when hitting this reading? What kind of oil are you using? Is the pump warm?


Yeah according to the welch website it should blank off around 0.03 microns. I believe the red hose is the natural rubber hose from thomas sci. I am not using any clamps on the hose/barb connection but it is very tight. I’ve changed the oil a few times on the unit since we got it and it has never seemed to make much affect, vacuum level stays about constant around 1600 microns during distillation and the oil doesn’t appear contaminated as in it is still pretty clear and light colored.

Ballast open while pulling volatiles during operation, usually close it around 120C. All readings above were taken with a closed ballast after the pump had been running for ~30 mins.


Small tip close your ballast after 165c so light volatiles are all dealt with, it’ll go easier on your pump.


Do you have a roughing pump? Might wanna get a cheap one

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You’ve definitely got a substantial leak or your pump is failing. Again are you using manufacture specific oil? The viscosity rating is crucial for rotary vane style pumps

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We use Welch Direct Torr premium vacuum oil. I’m not super familiar with the viscosity rating but it is the same oil that Welch recommends in the CRV manual. It seems like when I hook up my metal cold trap and clear vac line that my vac goes from 52 micron to 500 micron which is where I wonder if my tubing is inadequate.


Roughing pump just means a pump specifically for volatiles right?

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Something is wrong my friend. When I plug my vac gauge directly to my CRV 16 I get a rating between 2-9 microns. 10-35 during first pass.


Are you using vac rated tubing?

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Using two different types of tubing. One is the red rubber ones from Thomas Sci with a wall thickness of about 4mm that runs for about 2 feet between glass cold trap and swaglock. Then I have about 6 feet of this hose( To be honest I’m not super confident in the latter hose because it’s not quite as thick and seems more flimsy.

Imma try flushing the oil and blanking it off again.

What tubing do you use?


A welch 16 is a small pump for a 20 L rig
If you where to leave the pump running for 6 hours you Will reach low micron
Running a 20 l rig in tubing is not a good idea
The cfm you have are probably more than the diameter of the tubes can handel
And at last a pump direcly measured at 50+ micron is a pump that needs Some love
A small overhaul kit should help
I would reccomend working with3/4 inch dubbele braided transparant pvc hose
IT s cheap riggid and transparant
Also keep your hoses as short as possible
And if larger diameter hose can be used Please do
Are you aware that you have less than 1 cfm per liter flask ?
Where 8 cfm is considered minimum
I have a trivac d65B that i find is ok on a 20 L rig


8 cfm per liter flask would mean 160 cfm for a 20l flask but that trivac is only doing 38-39 right? Has anyone tried hooking up a roots pump to a short path yet? They might be too strong for our application but would easily keep up with volatiles if it wasn’t.


Yes a roots pump works but i found that overkill and not so Nice with diffusion @Kingofthekush420 can tell
I place a frequency controller ( second hand from the cow milking industry) on my vac pump to push iT s limits 60cfm


Maybe @BreakingDabs can Chime in and tell the amount of cfm on his 20 L rig
If i am not misstaken he was hitting 140 cfm


I feel like running a rotary vane with a roots pump would let you hold a super stable vac through the whole run and with that combo you would be sitting around 140 cfm. It might be better suited for a WFE or it just might be way overkill lol


The risk of to high cfm is that in a boil your crude can start to muffin i have only witnessed iT 2x myself
And iT s a scary (mess) sight till the coldtrap a sludge that cristelized (high sugar content ) and a bitch to get cleaned

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