DIY Vacuum Purging Chamber

To perform some of the desirable alchemy with cannabis essential oils, requires some sort of vacuum chamber that you can control the heat and vacuum levels in, as well as see what you are doing.

These are readily available as vacuum desiccators and vacuum ovens, but all are pricey, so how about just building your own?

We already have a glass desiccator with a hot plate inside, and picked up a new used vacuum oven, but alas the temperature controls are ineffective in the low ranges that we operate, so we are in the process of refining its controls.

More on that subject on a separate thread, but this thread is to show how we punted when the vacuum oven capacity that we had counted on, eluded us, with meds to process backlogged.

To that end, we used a old 22 quart Mirror pressure cooker that was gifted to us, and after removing the gasket, we tossed the lid.

I then drilled a 1/4″ pilot hole through the side wall wrapper, about 2.5″ below the top flange, followed by a 3/4″ bit, to enlarge the hole to fit a 1/4″ NPT brass bulkhead fitting.

I then inserted the bulkhead fitting through the side wall from the inside out, installing a gasket on the inside flange, and tightening the nut and lock washer on the outside of the pot.

To this I added close nipples, a cross, with two 1/4″ ball valves, and two 1/4″ MPT to 1/4″ flare refrigeration hose fitting.  One for the vacuum pump and the other for the vacuum gauge hose.

As it is temporary, and we needed it immediately, we reused the existing gasket, and made a new lid out of a 1″ X 16″ acrylic plate.  At -29.9″ Hg gauge, there is about 1/16″ lid deflection in the middle, so a thicker plate would be better to reduce high cyclic fatigue.

If it were permanent, we would have a new Viton gasket cut by Paramount, or Gaskets Unlimited and use 1 1/2″ polycarbonate, for the lid.

Hee, hee, hee, after telling me that they didn’t have any, and after having them cut the 1″ acrylic plate, I found a 22″ X 29″ X 1 1/2″ Polycarbonate remnant at Multi Craft Plastics, which I scored for $72.  It has one 6″ hole in one corner, but that is $2/lb for bullet proof polycarbonate panels, like those used at teller windows.  Snicker, snark, snort, more projects to come!

Here are pictures showing how we made and how it turned out.  We are able to easily control the temperature with an outside hotplate and reduce the pressure to -29.9 with one of our 6.2 cfm single stage AC vacuum pumps:

Vacuum chamber from pressure cooker

Vacuum chamber from pressure cooker

Vacuum gauge at -29.9" Hg

Vacuum gauge at -29.9″ Hg

Brass 1/4" NPT bulkhead  fitting

Brass 1/4″ NPT bulkhead fitting

5-19-13

Soooo, how about heat in the 85/115F range, way below what most hot plates and griddles control at?


We’ve tried several different hot plates, with and without trivets and pads to dissipate heat, and ran across a slick set up forum X, posted by Superly and using two layers of reptile mats to generate the heat, controlled by a simple light dimmer switch.

Hee, hee, hee, works pretty slick! After cutting them to size, I put a towel under them and then put two layers of towel over the top surface, but cut out a big hole in the top layer through which the pot sat, resting on the heating mat.

Here was the test run of Cheese, as well as a picture of the heating provisions and an inlet filter on the makeup air to keep out atmospheric dust!

Reptile pad towel insulation

Reptile pad towel insulation

Insulation and inlet filter in place

Insulation and inlet filter in place

Vacuum purged Cheese Absolute

Vacuum purged Cheese Absolute

5-26-13

Wowza, speaking of DIY, look at what Steve whomped up out of acrylic panels!  Looks purdy enough to use for a jewel display case and sturdy enough to last.

Steve's Vacuum chamber

Steve’s Vacuum chamber

Steve's vacuum box and lid

Steve’s vacuum box and lid

__________________________________________________________________________

8-2-13

The question arose regarding the suitability of a 2″ Polycarbonate plate lid on a 20″ pot, so I thought that I would share the answer and the math with you:

In summary, it looks to me like a 2″ Polycarbonate or a 2″ Acrylic plate would work.  Stress at the extreme fiber at 450 psi, is a small fraction of the 9,500 psi ultimate tensile strength.

Deflection would only be about .004″, so high cyclic fatigue shouldn’t be an issue.

Calculating stress at the extreme fiber and deflection of Polycarbonate vacuum chamber lids lids

The formulas for calculating stress at the extreme fiber and deflection for a simply supported flat circular plate from the Thirteenth addition of the Machinery Handbook are as follows:

1.0       Assume:

S= 0.39W

       t2

d= 0.221 W R2

           Et3

Where:

S = Stress at the extreme fiber

            T=       Ultimate Tensile of Polycarbonate =9,500 psi

            p=        Pressure in psi = 14.7 psia atmospheric pressure

            W=      Total load on plate= p X area = 4618 lbs

            t=         Plate thickness= 2″

            d=        Deflection

            R=       Radius of plate= 1/2Diameter = 10″

            E=       Modulus of elasticity = 375,000 psi

            D=       Diameter of pot= 20″

Mechanical properties taken from:  http://www.boedeker.com/polyc_p.htm

2.0       Therefore:

            d= 0.221 X 4618 lbs X 100 = .034″ deflection on a 2″ plate

                        375,000 psi X 8

            s=  0.39 X 4618 lbs =  450 psi

                        4

8-13-13

Here are some more heat mat sources, compliments of Skyhighler, which have greater capabilities that the one above:

http://briskheat.com/
http://www.omega.com/

162 responses to this post.

  1. Posted by Jimmy Joe on October 3, 2016 at 4:03 AM

    Hey Good morning GW and skunk Pharmers I have a question so I was doing a vacuum purge with a small ISO wash run i had turned off the vacuum pump to give her a break and fell asleep when I woke up this morning my 1″ acrylic lid looked all messed up so I released took it off and yep sure enough the bottom was real
    Soft lots of spider cracking and made it more of a translucent than transparent it dried up now and isn’t soft anymore. Is the lid still safe to use like that? Is there a way to many sand the surface down again so it will be transparent or should I just throw the lid away and fabricate a new one
    PS thanks for all you guys are doing it has made a huge difference in the quality of life for me and the people around me Keep up the good work

    Reply

    • Thanks for the good thoughts!

      You have two issues at this point, so I would replace the lid.

      The first is the Isopropyl attack on the surface. Here is a chart showing the chemical resistance of Acrylic. https://www.tapplastics.com/uploads/pdf/acrylite_chem_resist.pdf

      That could be polished off, but the stress cracks demonstrate eminent failure under load, so better to toss it before it wrecks an otherwise perfectly good day.

      1″ is relatively thin. How big is your pot?

      GW

      Reply

      • Posted by Jimmy Joe on October 5, 2016 at 4:48 AM

        Ok thanks for the info GW I was going to wet sand and than buff it out but with that info and the stress cracks now it’s better to be safe and get a new one . My Vac chamber is 6″x6″ round stainless so I figured the 1″ was ok. I am currently building a Lil’ Terp using all the great info on your site thanks again and Keep up the good work 👍🏻

        Reply

  2. Posted by sandy on August 13, 2016 at 8:23 PM

    How longdo you purge your wax . and wats the temp. you should have it . and I’m new to this so what should I do .?? Anyone??

    Reply

  3. Posted by 1n1valrud on May 26, 2016 at 10:43 AM

    How do you get the stress and the deflection on the side panels of the rectangular polycarbonate vacuum chamber? Is there no stress/deflection on the side? I want to make a bigger (20X20X20″) vacuum chamber, but I am not sure what thickness the side panels need to be. Same question about the bottom panel. Does the atmospheric load only apply on the top, and not other surfaces? Or would it be the same on every face? I couldn’t find any information on it. Any help would be appreciated

    Reply

  4. If you have a magnetic pressure cooker, or, pan/container that you can use, then I highly recommend it, and; use induction heating. No flame/spark 100°F is the auto low button (you can go lower). Time is programmable as are heat changes at different times. I use it exclusively cause it’s so exact & programmable in 5°F increments, stops heating insantly, and only heats where pan is, very cool. I’ve even put a metal baking pan and then my pyrex water dish for initial purge before vacuuming.

    Reply

  5. Posted by Wowie Zowie on May 3, 2016 at 1:03 PM

    for heat use a reptile warming blanket

    Reply

  6. Posted by Richard on April 2, 2016 at 2:30 PM

    Beyond the speed-up of the purge does the vacuum chamber bestow any other benefit?
    I don’t mean the benefit to time-temperature trade-off to thermally-unstable components.
    I mean is the change in various component’s relative vapour pressures (as the temp/pressure is varied) beneficial to the retention of desirable components and removal of undesirable ones?

    Reply

  7. Posted by BlueFoxHydro on March 26, 2016 at 2:11 AM

    Graywolf, you are as much a beast as the name implies.

    Superlative information, creativity, scientific process, and humanitarian striving.

    Definitely my new favorite site — and one I will refer to extensively as I dip into building an extractor for my business.

    Thank you for all the data,

    BlueFox

    (Nice naming convention, by the way🙂.

    Reply

  8. Posted by Clunt on November 23, 2015 at 9:56 PM

    What gauge would you recommend if I only want to pull down to 29.2?

    Reply

    • Depends on the design and size. Typically, around 10 gauge is used for the wrapper, but has stiffeners welded to the outside for rigidity.

      A round cylinder would require less wall thickness, because of the way the stresses are distributed.

      Reply

  9. t end, we used a old 22 quart Mirror pressure cooker that was gifted to us, and after removing the gasket, we tossed the lid. I then drilled a 1/4″ pilot hole … ccookerp.wordpress.com

    Reply

  10. Posted by yonder42ok on August 17, 2015 at 11:16 AM

    How long will it hold-30 for how many hours my chamber only hold for less than a hour

    Reply

  11. I am not very sure about the need, I mean, do I have to use one? Like , for the vacuum selaer I use in home, does it really need to be cleaned once a while.So if someone can suggest me which one I should use, the ones from market;or this home made one?

    Reply

  12. Posted by SIA on April 12, 2015 at 11:39 AM

    Thanks for all the great info here.

    Does the pot being made out of either aluminum or stainless steel make any difference, other than stainless steel working on induction cooktops and aluminum not?

    Reply

  13. Posted by Geoff on January 22, 2015 at 2:21 PM

    How long should I let the butane evaporate off before putting the oil in the vacuum chamber? Do I need to worry about butane contaminating my vacuum pump’s oil?

    Reply

  14. Posted by Michael Lawrence on November 22, 2014 at 2:04 PM

    With the set-up ypur friend steve made out of the leftover acrylic, did he also use the same hardware, like the brass bulkhead fitting, with his set up?
    Also i was wondering where could i get just a negative pressure gauge? All i can find in hardware stores are air control manifold gauges… i saw that break bleeders have a negative pressure but i dont want to spend 30$ on the system when i only need the gauge

    Reply

  15. […] certain kind of gaskets, etc. that work and don't dry out or leak or anything like that. rnrnDIY Vacuum Purging Chamber | Skunk Pharm Research LLCrn rnrn rnrn rnrn rnrn rn rn rn rn […]

    Reply

  16. Posted by ERIC on September 28, 2014 at 2:21 PM

    HI I SELL $5,000 dollar VACUUM PUMPS used for $500.00
    Pumps are an ALCATEL 2021I 2 STAGE ROTARY VANE 14CFM They are in good Used Condition and Fully Tested before Sale.
    I also Sell INTAKE AND EXHAUIST FILTERS for this PUMP.
    STYLEENTERPRISES@YAHOO.COM
    I do not Ship Them
    ERIC

    Reply

  17. Posted by Jack Strap on September 27, 2014 at 6:13 AM

    The old rubber gasket from the pressure cooker, from what I read in the article. The vacuum will hold the seal tight.

    Reply

  18. Posted by Jim on September 5, 2014 at 8:46 PM

    What did you place on the lining of the top to hold suction?

    Reply

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