Vacuum measurements for SPD

Hello folks!

I’m trying to get my first SPD setup up and running and I think I have an issue with maintaining vac.

The head temperature doesn’t hold, and drops to around 25C despite the mantle being set to 200C.

I have an inline analog pressure gauge and it reads -28 inHg. I’m having trouble deciphering between different units of vac. How do microns relate to inHg. Do I not have a vac despite the gauge suggesting that I do?

Can I get a meaningful reading of vac from an analog gauge in inHg or do I need a digital gauge?


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Microns “start” when a regular gauge is at 29 or so you need a micron gauge. Cps sells a reasonably priced one , but if you can get a bullseye it will tell you if you have a leak . There about 450 or more if you want the Bluetooth one . But you also have to let it build vapor pressure to heat the column, just cause your flask is at 200c you light not have given your column time to heat up to allow a “pathway “ for things to exit . What kinda pump and what kinda set up


Running Joanlab glass and mantle (yes, Chinese) with a 3 receiver cow and an ice cold trap. Not sure what other details would be pertinent. I have a Zeny 125+ that’s rated to 5 Pa and 3.5 CFM. I understand from what I’ve read this may not be sufficient, but want to have confirmation before moving ahead with a more expensive pump. What are the minimum specs I should look for in a pump?

Could you explain exactly what the micron level is referring to? I understand it refers to the size of particle that the pump is able to remove, but I’m not clear on how that relates to the strength of the vacuum.

Thanks again.

Most of the ppl here run Chinese glass. Most is all rebranded anyways.


From what I know, micron is a unit of measurement of pressure. Atmospheric is 760,000 micron.
The lower the micron, the stronger your vacuum. 0 micron = perfect vacuum.
You’ll also see people talking in millitorr, but the number is extremely similar to microns
( 1 mtorr = 0.9999997631384713 micron ).

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Inches of mercury is a measure of pressure, specifically ‘how many inches does the given pressure cause a column of mercury to rise?’ There are plenty of great articles online explaining that concept more clearly, but if it’s a measurement using inches it’s safe to say there’s a metric equivalent using millimeters, which is the definition of mmHg, also called Torr. One thousandth of a Torr is a millitorr, aka Micron (the name micron comes from the fact that mtorr is equivalent to micrometers of mercury, umHg).

More on what Concentrated_humbold said: -29"Hg is equivalent to about 23 Torr, which is 23,000 Micron. Your 5 Pa pump is rated to about 37.5 Micron. That’s under ideal laboratory conditions, and you probably want a pump rated to something like 0.1 Micron if you want to start getting down towards acceptable vacuum levels.

Hope that helps.


Ah. So micron refers to a given vacuum level, not a size of particle or mesh as I’m used to.

I’m currently looking at the Alcatel 2021i pump and it has a few pressure ratings ( If I understand correctly the 1.5 x 10^-3 Torr rating would not be sufficient for SPD?

Any pumps you would recommend for a 2L SPD?

I have several Alcatel 2021i. The max vacuum on the is 6.5 micron and they are plenty for a 2l short path.

You might wanna check out my thread. I made a lot of mistakes the other day running my spd. You can save yourself some troubles by possibly reading it first.


Thanks. I gave a look through your thread prior to posting.

I think my first step is ordering a vacuum gauge and using it to show that we need to buy a more expensive pump.

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On a 2liter i recomend a pump of 8cfm minimum and a final pressure of
1 - 10 4 sort of like the Alcatel 2008a
Two pumps work better one for lighter fractions and swapping in line for the cannabinoids If your coldtrap fails a little your oil looses vac cappacity so starting with a fresh warm (30 min ) pump helps
In the last part of traject