Vacuum gauge placement

Hello all, I’ve recently gotten into spd and was wondering if there is an ideal placement on the setup to install the vacuum gauge? I’d been using a manifold I built out of spare extraction parts (1/4” tee, two barb fittings, 1/4” nip) to connect my monocow, dewar cold trap, and bullseye. With that, I was hitting 2300-2700 micron and on a good day 400 micron. Yesterday I installed a 1” tee directly on the pump, with the other two arms connected to the vacuum gauge and the dewar. It’s been reaching down to 30-40 microns easily since then.

I get a feeling it may not be reading the vacuum accurately since it’s directly connected the pump in a sense. Where in the system do you guys have the gauge sitting that works for you? Any advice/insight is appreciated!

I’ve recently started running one after the cow on a T (running a digital gauge inline can get acetate on your sensor and ruin it), and one before the pump but after the cold trap. They typically start out with a major difference in readings (cow: 1700-2100 micron, pump: 200-500 micron) as I ramp through the volatile and heads fractions, and then even out as I get into the main body (cow: 100-400 micron, pump: 100-400 micron). It helps to do some runs and log both gauges, mantle temp, and vapor temp every 5 minutes or so to get an idea of what your typical run looks like. Then you will start to see when abnormalities arise in different locations in the system. Then you can use that information to diagnose said abnormalities, particularly leaks, and if you really have a leak or if you’ve just hit a volatile fraction. Hope this helps.


Ah yes, the problem of the mystery crude. I’m never sure if they’re properly purged or not so that may be the main issue. I log my runs every time but not so often as every 5 minutes. Just how long it takes to get to each fraction, mantle temps and microns at each stage. I also start off at pretty high microns but trickle down to the double digits during my main. I guess I’ve always thought I should be hitting below 100 from start to finish.

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The reason for the increase of vapor pressure during heating leads me to think that you’ve not fully removed the first fraction before ramping up. I slowly ramp to and hold at 130-150 c until the volitile fraction is gone, your vaccum will improve at this point. Then slowly ramp your way into the cannibinoids and make your fraction cut. Depending on your vaccum level you might have to slightly decrease your heat to stay in the fraction you want.


The ideal placement of a vacuum sensor is achieved when there is little to no chance of sensor contamination. Since the pressure reading is a comparison of pressures, internal vs external at the point of measurment, I am most interested in comparing that difference as close as possible to the barb fitting used to hook my distillation rig to the stainless steel used for the vacuum system. To me this is most relevent as it is the closest possible point to where the expected evaporation will be occuring.

Then the sensor itself is installed on two tee joints. The first t joint tags into the main vacuum line and is vertical to the path of normal flow. The second t join mounts vertically. On top is the Pirani sensor. On the remaining side joint is the system vent valve. These are kf16 fittings and each needs a centering device for the seal. On the t joint holding the sensor each of the three centering rings is fitted with a fine mesh stainless steel screen to discourage contaminates. The vent valve when open flushes fresh air into the system right past the pirani sensor and no valve combo possible can pull contaminate up into the t joints. Only fresh air and only flowing back towards the contamination.

If I ever had a sensor get contaminated I could also just stuff some Kimwipe up beneath the sensor and then just change it as needed I guess but so far this configuration has nailed it down for me. Here is a video that quickly covers everything but can show you my sensor set up.

Here is what those centering devices look like from my order history.