hey guys. been reading up on the topic but a straight answer is still elusive. im trying to figure out how peeps are setting the vac oven pressure to -15hg or -20hg or anything under full vac. i understand we can pull vac then shut the valves and have it sit at whatever pressure we choose, i get that. but aren’t we supposed to keep the pump constantly on to continue removing solvents? im confused after reading the cascade tek vac oven sop that talks about solvents resettling back on your product. then im wondering the validity of that statement. if solvents were to resettle on our product it would immediately off gas in the environment when the oven is opened or when some air or gas is introduced to the chamber or if full vac is reached. right?
my goal is to preserve as much terpenes as i can. i going for a sugar sauce. i have an AI 1.9 that like 5 years old. im using the vac pump it came with for now but ordered a used idp3 off ebay that im currently waiting on.
a controller that turns your pump on and off is the most efficient way to achieve this.
next is a valve that opens/closes to achieve
then a controlled leak.
if you shut off the pump, vac levels will change over time. which slows you down. other than that it doesn’t really hurt much. keeping the terps and losing the solvent is a balancing act between time/temp/vac level. given that input material makes a huge difference in exactly where that balance lies, you’re going to have to feel around a little bit. read, experiment, evaluate. repeat.
But the bosses only want to pay for one attempt… And they need to know how it’s going to go, first… 
today we destroy cannabis.
maybe tomorrow we make product…
Try an SMC IRV20 vac regulator. Get one with the pressure switch and hook it up to a relay for the pump and solenoid to keep the oil from backstreaming. Should cost around $300 with all the bits and it’s good as long as you don’t want to go below 40-50 torr.
there are two main variables that control the evaporation of solvents and terpenes. Those are pressure and temperature. You lower the pressure in order to lower the temperature at which they boil. With this logic, too low of a pressure is equivalent to too high of a temperature.
Check out this graph for ethanol. It is the third figure on the page. https://wps.prenhall.com/wps/media/objects/3311/3391416/blb1105.html
Say you keep your temp at 104F (40C). You start at 0 in Hg (760 torr) and start to reduce the pressure. By the time you get to 22 in Hg (200 torr) you have already brought the boiling point of ethanol down to 117F (47C). As you continue to reduce the pressure to 26 in Hg (100 torr) you have dropped the boiling point to around 86F (30C), which is already lower than the temp you have set. A “full vac” of 30 in Hg (0 torr) will drop the boiling point of ethanol theoretically to 32F (0C). This seems great right? lower pressure means no more ethanol, right? yeah that’s true but the same principal applies to terpenes as well.
Limonene is somewhere in the middle of boiling points for the wide range of terpenes present. At 0 in Hg (760 torr) limonenes boiling point is 348F (176C). That is well above the set temperature. At 30 in Hg (0 torr) limonenes boiling point drops just below 122F (50C). Still above the set temp. But like I mentioned earlier limonene is not the most volatile terpene, so some BPs may be below the set temp. We all know terpenes will readily evaporate well below their boiling point.
My point is more vacuum is not always better.
Also If you leave your vac at 15 in Hg and a set temp, volatiles will continue to evaporate over time. Come back a day later and the pressure will be higher do to the increase in vapor.
thanks for that input!
not looking forward to dealing with those guys. so far peeps have been cool with me having to test to know. but ive only talked to like 3 growers so far. just started reaching out tho. already got 2 small contracts tho!
ive been practicing on old bud that wasnt great so its just been sitting there. found some old trim from some nice stuff too. i was able to do 4 practice runs. now im on contract material.
that sounds cool. you lost me at hooking it up to a relay tho… hows that work?
very good info! thank you
is there ever a reason to pull full vac??
does it make sense to set my recovery temps and purge temps the same? ive been recovering at 69f to preserve terps. then its in my vac at 0 psi at 85f. does this make sense? should i just raise my recovery temps to match my oven temps or will i create a tastier product with what im currently doing with the low temp recovery?
Hook the inlet to the vac pump to a solenoid valve (we use the fancy ASCO vacuum solenoids, but something cheap from electricsolenoidvalves.com is probably fine for an oven). You will want a normally closed valve so that if you lose power the pump won’t backstream (bonus points!). After the solenoid, connect to your regulator and then your cold trap (these are NOT chemical proof).
Assuming the pump is 120v, get a 24v DC to120v normally closed relay (something like http://url.ie/16v8n). You will also need a 24vdc power supply. Connect from the +24 on the power supply, through the pressure switch on the regulator (you will want the PNP option, not the NPN) and to the first relay coil contact. Connect the other coil contact to the negative on the power supply. Then connect your 120 hot wire to the first switched contact on the relay, and the hot wire from the motor to the other switched contact. Also connect the hot wire from the solenoid (usually it doesn’t matter which one) to the second switched contact. Then connect the other wire from the solenoid to the 120 neutral.
It takes a little tinkering with the settings, but you should be able to get it set up where it doesn’t short cycle the pump too bad. It’s a great setup because it will keep you from undershooting if a valve gets closed to quickly or something. It’s awesome for a rotovap. Here’s a wiring diagram:
wow. thank you for that thorough explanation. you must really know your shit.
I have like 6 of these running in our lab right now sans pump cutout. I wish this counted as “knowing my shit” but unfortunately the company only wants “my shit” to be things I’ve never done before lol.
Preach it baby!
I felt this today!