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


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


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



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


d= 0.221 W R2



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:

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



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

136 responses to this post.

  1. Posted by Kris on July 20, 2014 at 8:32 AM

    How do you recommend heating the receiver in your mkiii set up to produce shatter


  2. Posted by Sean on July 1, 2014 at 7:48 PM

    Hi , I’m running a mkIII and a cascade tek oven. My shatters have tested amazing ,zero solvents detected.But presentation is what I am having a problem with. Here in van bubbles of ANY kind are not good. any tips on getting the small fizzy bubbles out?


    • Posted by Sean on July 3, 2014 at 2:18 PM

      I’m guessing I posted this question in wrong thread sorry to all


    • The small fizzy bubbles are CO2 from decarboxylation. If you run the puddle high enough for them to escape, or at around 115F at -29.5″ Hg, they shouldn’t be an issue.

      You could also decarboxylate the oil and eliminate them, but it wouldn’t be stiff anymore.


  3. Posted by punkvapes on June 25, 2014 at 8:26 AM

    Something that I’m not seeing discussed much here, or anywhere in fact, is over-purging. Is there even really such a thing? I’ve built my vac chamber, and I have been following all the guidelines mentioned here with close attention to detail. What I’m finding, though, is that if I leave a concrete or oleoresin in my chamber overnight, it begins to darken and get sticky again. It even happens when I use lower head/vacuum. I’ve heard of people vacuuming their extracts for up to 16 days, but I don’t see how they end up with anything but roofing tar after that long of a purge. Can anyone explain what is happening here?


    • Posted by Jameson Johnson on June 27, 2014 at 8:38 AM

      What temperatures are you keeping your oleoresin at in the chamber? I keep mind 95-110, and don’t have troubles with stability. Any hotter, and I may have the problems you describe, however.


      • Posted by punkvapes on July 1, 2014 at 7:12 AM

        Thanks for the response. I have been running at 115f, as recommended here, and I use an infrared thermometer to verify. I’ve tried as low as 108f, but perhaps I need to try even lower. Do you run your vacuum any different when running at lower temps? I have a very accurate digital vacrometer and I am careful to go no more than 29.8″hg (adjusted for altitude).


      • Posted by punkvapes on July 2, 2014 at 6:12 AM

        Ok I did a new run. 100f, 29.2″hg (adjusted) for about 11 hours. I got similar negative results, but possibly not quite as bad. To give you a little more info, it starts as a dry look around the edge of my puddle, and then the entire thing begins to become cloudy. Again, I’m monitoring temperature and vacuum very carefully, my input material is high quality and thoroughly dried. My puddles are very thin, under 1/8″.


  4. Posted by moppy on March 1, 2014 at 10:49 AM

    Just found your site. It extremely useful and informative, thanks! I realize this thread is a little old but I noticed in the comments, folks are having issues with heating. Hopefully this is useful:

    Have you ever though about an inexpensive PID temp controller, thermocouple and solid state relay for you heating control? They can be had for 30-40 bucks. I use them in several projects. They are inexpensive, readily available and the best part— they learn the system they are in and make accurate temp adjustment fairly quickly.


  5. Posted by Alternative Medic on February 28, 2014 at 3:43 PM

    You mentioned if it were a permant setup you would use polycarbonate over acrylic for the lid, is this strictly because of strength and retention properties or is there the risk that the acrylic material could start to seep into my product after prolonged use?


  6. Posted by Pookiegus on February 16, 2014 at 4:23 PM

    In a recent search on eBay this gadget for purging turned up


    Basically someone added a polycarbonate lid with gasket, valves and vacuum gauge to a heated ultrasonic jewelry cleaner.
    The guy is claiming this is the newest method for purging BHO and can lower purge times to 1 hour. . .

    I like the precise digital control on the heater 90-140 Degrees – It has a timer as well.
    The ultrasonic transducer under the stainless tray vibrates at either 20,000 times a second or 40K
    It does seem like the vibrations would help “Shake” the butane bubbles out of the extract since it’s so thick. . . but I’ve been unable to find any info on people purging with one of these. . .

    Has anyone used one of these things?
    Do you think this would speed up the purging process?
    Have you ever used an Ultrasonic device in your BHO purging?


  7. Posted by david on February 14, 2014 at 3:07 AM

    Im very interested in construction a chamber pot like steves. Can you help me out with a link or intruction. What thickness of product what adhesive or anchors to use making something like this. I would be very greatful of you time do so.


  8. Posted by Ron Kingroll on February 5, 2014 at 6:40 AM

    This may be a dumb question but I’ve always had a difficult time pulling a vacuum that was 29.5 or so. I did some research and found that at my 3000 foot altitude I can only pull 26.8 lbs. Am I interpreting this correctly? I’ve got into the habit of listening to the sound of the vacuum pump and using it as my max vacuum. Also, I’m using a Mk3 with 2×24″ columns and would like to increase their size. What would you recommend?


  9. Won’t a flame kill of the residual butane when smoking?


  10. Posted by dope cook on January 23, 2014 at 1:23 PM

    Hey GW! I built a similar set up (except we use a sous vide water bath for our heat source :), and it has produced oil with less than 25ppm residual butane. (Woot!).

    My question is:

    I noticed that your chart states that THC boils at super low temps while under high vacuum.

    Are we boiling off the good stuff when we pull a -29+ vacuum??


    dope cook

    P.S. you guys are my role models! sending love from Seattle.


  11. Posted by Waleed on January 15, 2014 at 6:47 PM

    I read on one of your posts that glass has the same elasticity of aluminum does that mean if i were to use a aluminum pot as a base(w/ a polycarbonate top) that it would possibly implode on full vacuum? i heard someone say it would be fine at 29…also how bad is an implosion there isnt much information on the internet about it and the only video i saw was with a unfit chamber made of glass & tape


    • Posted by Waleed on January 15, 2014 at 9:35 PM

      specs are: 3gallon tank height 9 1/4in and diameter of 9 7/8in with 1/2in polycarbonate top


    • Depends on how heavy the pot is. What I said is that glass and aluminum have close to the same modulus of elasticity, which means that if you simply supported the same size beam of each on both ends and set the same weight in the center, the two beams would deflect close to the same amount. When the two beams reached their limits however, the glass would exceed its ultimate tensile and break, while the aluminum would bend.


  12. Posted by Dasher710 on January 13, 2014 at 3:09 AM

    Hi, thanks for all the great info GW
    was looking into ambient heat for the chamber and was wondering what you thought of Seedling Heat Mats vs the reptile mats you guys used!
    and will an aluminum pressure canner be okay for the base without implosion?
    and would using 3x 1/2 inch polycarbonate fastened together be strong enough for the lid or should i search for a thicker polycarbonate?
    finally would you contact cement the gasket to the polycarbonate or aluminum pot?

    Thanks in advance for your time!


    • Depends on the specs on the heat mat. Briskheat and Omega both make a killer silicone rubber heat mat that works stellar.

      Probably. What diameter and how thick is the canner wall and bottom?

      They would have to be attached to one another, so that they acted as a single beam’

      I would rough up the aluminum and stick it to it. The polycarbonate will be flexing.


      • Posted by Dasher710 on January 13, 2014 at 12:58 PM

        Thanks for the info on the heating mats! Do you prefer either mat to your mcgyvered reptile pads and do they provide a more consistent temp?

        Couldn’t find exact specs on the wall thickness of the pot but its this 16 qt presto on walmart, even called their customer service w/ no luck. (

        in regards to attaching the multiple pc sheets which would you recommend between a screw and nuts tightening the pieces together on each of the four corners of the lid, or using an epoxide? i also found this third method maybe you could help enlighten me if this is a viable option. (

        Thanks again for all your help!


  13. GW want to replace polycarb bel art chamber Whats better aluminum or steel aluminum better faster heating?? Thanks for all u do


  14. Posted by Faxon on January 6, 2014 at 11:05 PM

    Thanks a ton for posting this! Ran into issues doing a QWISO run when the cheap hand pump for my filter broke. New month and new budget, so I decided it was gonna upgrade to a nice vac purging setup and the pump im getting doubles as a nice high power pump for vacuum filtration of QWISO extractions as well. Now I can filter bulk batches down to 5 microns AND make shatter (^_^)


  15. Posted by Alex on January 5, 2014 at 8:25 AM

    Really interesting site!!!

    Hi, just ran across your site looking for deflection calculation examples. I follow your calculations, however I don’t understand where you get 0.0284 in your deflection formula. I have looked in Machinery Handbook, and in their example using steel (same formulas as yours), they use 0.221. I don’t understand where their figure comes from either. I’m not a math person, and must be missing something basic. Could you enlighten me about how to come up with the number (varies with material I realize)?


    • Hi Alex, you are absolutely right, good eye! I changed the post to reflect the correct number.

      If you go to the Thirteenth Edition of the Machinery Handbook on page 444, you will see where the number came from. I inadvertently picked it up from the formula immediately above the one I was writing down.


  16. Posted by Johathon Springer on January 2, 2014 at 4:47 PM

  17. […] DIY Vacuum Purging Chamber. […]


  18. I’ve been looking around at available tops for a vacuum chamber I’m building. The pot used is roughly 16″ in diameter. It seems that 2″ acrylic is a really great price point when compared to 1-1/2″ or even 1″ polycarbonate of equal square footage.

    What I’m really curious about is glass. Currently, I’m waiting on quotes from a company that carries 1-1/2″ to 3″ glass. Do you have a recommendation or suggestion/minimums on glass as a vacuum top?


    • Yeah, acrylic is cheaper and stiffer. Though not as strong, it is strong enough.

      Glass has a modulus of elasticity around 10,000,000, so using the formula in the thread, 1/4″ glass would deflect about .034″ at full vacuum.


  19. Posted by Mario on December 16, 2013 at 3:03 PM

    I was using a 3cfm vacuum but it was a joke, what cfm vacuum and brand would you recommend, thank you so very much GW


  20. Posted by Tofaxik on December 12, 2013 at 12:06 PM

    Even thought the vacuum pump is pulling air out , once you reach a certain level of vacuum, isn’t it possible for the oils that lubricate the surfaces in the pump to partly boil off and partly distribute back into the container? This is a pretty cool idea but were I to do this I would worry about contamination from the vacuum pump.

    Would like to get your opinion. I saw another page where a guy uses one of these pumps in combination with a vaporizer in a rig he has. That led me to this page, you guys have quite a bit of interesting information.



    • I’ve never personally had a chamber back flow on me, but playing the devils advocate, once the system reached steady state, it may be possible for vapors travel through the line into the chamber. What was the elevation of your pump, relative to our chamber and what vacuum level were you running?


  21. Posted by Amanda on December 1, 2013 at 6:54 PM

    the heating source ive found works the best and is precise is an induction cook top like the nuwave totally worth it


  22. Posted by Doc Green on November 21, 2013 at 6:45 PM

    I was looking around for a good and affordable heater, found this one (250 watt) for $35, and they offer a 500 watt model for $45. Sealed in silicone, built to be glued to the bottom of a vehicles oil pan, and free shipping.

    Still needs a thermostat, or a dimmer and a person to babysit it for safe operation.

    Doc Green


  23. Posted by Doc Green on November 21, 2013 at 4:28 PM

    I have not worked with these folks, but the seem to offer a great vacuum chamber at an affordable price. And they’re local too.

    On the deflection question, with the larger chambers. Has anyone considered a steel or aluminum lid with several six inch “portholes” cut in it? It would require multiple gaskets, so a little more expense here, one large one for the big pot, and one for each of the smaller holes. Mostly this adds additional cost for the cutting of the steel (or aluminum), but saves a whole lot by using 3/4 inch polycarbonate for the windows. Or even 1/2 inch polycarbonate, if you go with little four inch windows. And you could get fancy and bolt the plastic windows in place on the larger lid.

    How many such view ports does someone really need? I’m thinking just two, one for the light source, and one to look into. Six inch for the viewing, and the second one only around two inches, large enough for a high power LED flashlight to sit on it.

    I’m not up for the math right now, anyone want to calculate how thick a 24 inch circle of regular (relatively) cheap steel needs to be, to limit deflection to a reasonable amount?

    Doc Green


  24. i found that a heating pad from walgreens works great when dismantled…basically take the blanket type wrapping off and cut the wire out leaving the insulating covering. wrap it around the sides and coil in on the bottom. leaving it on warm keeps it at about 102 degrees F. i’m sure if you wanted less heat you could wrap some kind of thicker tape before the wire goes on.


    • though i used the original lid because of it’s heat sink capabilities to keep a more even temperature, not sure how much differently it affects the overall heat compared to polycarbonate


  25. Posted by Gbroque on October 26, 2013 at 5:15 PM

    what is the point of using a griddle if it runs so hot? i see tons of people using them, so i just bought a griddle (thinking i could lower the temp somehow) and today compared the temps to a hot pad i had lying around. the griddle never got below 200f without me turning it on and off, but the hot pad on a med setting with the polyester (spark causing?) cover or without it on the low setting was just about 100f, perfect right?


    • Good point on the poor low temperature capabilities of most griddles, and what we had to use, was a trivet to reduce heat transfer to the pot, and insulated our product from the bottom with a couple of silicone rubber mats.

      Mats have far better low temperature control, and what we use, when we aren’t using the vacuum oven. 100F is the low end of the range. We run ours closer to 115/120F.


  26. Posted by Steve on October 23, 2013 at 1:47 PM

    Have you ever considered using some type of ultrasonic waves to stimulate the oil as it is being vac purged? My thought was to make a vac lid for a very small pyrex dish, and sit that dish inside of a heat controlled ultrasonic jewelry cleaner filled with water. Any thoughts?


    • On the list of things to do and I suspect ultrasonics will work well to speed up evaporation, as long as the pool is liquid enough for the bubbles to escape.

      Water in a vacuum chamber is not a good thing, but I thought I might use it to purge a winterized batch of alcohol tincture.


    • Posted by nate r on October 30, 2013 at 1:38 AM

      that sounds like an awesome idea. the sound waves may also translate into synchronized pattern, much like sand sitting on top of a thin surface on a speaker. imagine how beautiful the product may turn.


    • Posted by Ryan on November 11, 2013 at 1:27 PM

      I use a microwave set below power level 3. It obv must be almost completely purged before using, but works to get out solvent below sensory threshold without vacuum. At least alcohol anyways. Same idea though as ultrasonic although most likely less effective. Hmm I wonder if ultrasonic will provide enough agitation to solidify the THCA like a wax?


  27. ok so I have found that the 2in polycarbonate in 24 by 24 is rather expensive. What would the thinnest sheet that I can use with a 21.5in diameter pot?

    I have the following quotes

    1/2in X 24 X 24 = $82.20
    3/4in X 24 X 24 = $368.00
    1 1/4in X 24 X 24 = $400.12

    Thanks again!


  28. I will be assembling all my new parts within the next few days. I originally planned to drill my chamber and install a bulkhead fitting using orings. I have recently been suggested to weld the two together. I have a aluminum chamber and a brass fitting. What would your suggestion be. Also keep in mind my new chamber is the 20 in one we talked about before. With a 1 in brass fitting. Thanks in advance for your continued assistance and research!



  29. Posted by smoke on September 19, 2013 at 10:59 AM

    im having a slight leak in my system that allows it to loose the vacuum overnight what gasket should i be using for the 1/4 NPT bulkhead fitting i tried a 3/4 gasket and im still getting leaks is it my lid gasket? im using the rubber seal that came with the pressure cooker


  30. Posted by unclefester2u on September 3, 2013 at 10:30 AM

    Greetings Skunk Pharm
    For those of us that didn’t make it out of the 70’s and 80’s as good as we would of liked too is there anywhere on your site the detailed instructions on this vacuum purging.
    I’ve made my chamber as per your instructions just trying to grasp the whole process now as in do you keep the pump running the whole time, where does the ethanol go, how long does it take. And what to look out for in the process.
    Thanks for all you do


    • Good point, and on the list of thangs to do. Also something that we are currently doing a lot of development work on, so we have a number of things to talk about.

      It would be faster if there were two of me, but the food and medical insurance for a clone is prohibitive and folks in these parts can barely stand just the one of me. I promise to do it as soon as possible and if you have questions in the interim, please feel free to ask.



  31. What is your filter/drier going to catch? I use this heat mat with the controller Thanks


  32. Posted by Jesus on August 31, 2013 at 9:02 PM

    I have a piece of glass that is (1/4)inch thick. I was going to use that as a lid for my chamber. The chamber is being built from a pressure cooker that is about 10inches in diameter. Im worried that the glass lid will eventually implode and break everywhere. would you recommend me using polycarbonate or acrylic instead of glass for safety reasons? Or do you think the glass lid will be strong enough under pressure? Unfortunately Im not good at math and will never be able to figure out its strength. Great site by the way, it has helped so much. Very thankful for the help and knowledge that you give to everyone! bless


  33. Posted by seacanna on August 28, 2013 at 3:52 PM

    Any worry about manufacturing chemicals or toxins that might be in the line filter-drier? It was made with only freon in mind after all. Would something simpler like this breather filter on the air inlet valve get the job done with fewer unknowns?


    • Actually filter-driers are intended for most refrigerants, which R-600 and R-600A qualify for.

      There is certainly no problem using a cheaper/simpler filter, the Emerson was handy and works.


    • Just use a coffee filter taped to the end of your ball valve. All you are worried about is dust being sucked in. I see no need for a filter, there should be no moisture in your room to worry about. Hope this helps.


  34. Posted by Home on August 28, 2013 at 10:37 AM

    does the lid need any fastening device?


  35. Posted by Pistolpete1178 on August 22, 2013 at 1:19 PM

    What would I look up to find the style of atmosphere filter you used? HVAC? Thank you for your time and effort!


  36. Posted by cory on August 6, 2013 at 2:28 PM

    I’m considering putting the bulkhead through the lid instead of the chamber. Then it would be easily portable to any other container that can hold vacuum, and the pressure cooker could still be used for cooking later. Any reason not to do it this way?


    • It is not as strong, but if your lid is thick enough it shouldn’t be an issue. That is how I did the smaller Mk IIIA lids, and the lid for the Mk I and II. Both are still functioning well at this point.


      • Posted by cory on August 7, 2013 at 8:36 AM

        It is 1″ thick polycarbonate covering a 12″ diameter circular chamber. At first I thought this would be more than adequate but after further reading I worry it may not be enough.


        • It is easily strong enough, but will still deflect. The formula predicts a deflection of .0045 inches at -29.92″ Hg,or 14.7 psi, but the one inch acrylic panel that I used on our 12″ pot, deflected over .062 at that pressure. Ostensibly Acrylic is stiffer than Polycarbonate, albeit not as strong, so it should deflect less.

          .0045″ deflection wouldn’t be an issue, but .062″ might be eventually, so I would use at least 1.25″ for a long term guarantee. Even at only .062 deflection, the 1″ panel would most likely last a long time, so it’s worth trying if that is what is available.

          We are using a 1.5″ Polycarbonate remnant for a lid, and it is virtually deflection free.

          We are now using the 1″ Acrylic lid on the 10″ dia Mk I and II lower tanks.


      • Posted by ron on August 8, 2013 at 2:31 PM

        You had a 1/2″ x 6″ circle of acrylic on a Lil’ Terp pot with the bulk head going through the center, will do the same myself but with polycarbonate since they recommended it and its the same price. What size hole did you drill in that 6″ lid and would you suggest putting in a tee while I’m at the job? Might save the pump from a deluge of oil if I’m reading right Vendor said, “We can cut a 1/2×7″ for you in either acrylic or polycarbonate (lexan). The price is the same for either – $8.15 plus $6.35 postage = $14.50. If the center bolt is going to apply pressure or stress, we’d recommend the lexan, as it won’t crack or fracture,” end quote.


        • We just drilled a 3/4″ hole with a hole saw, and installed a 1/4″ NPT Bulkhead fitting.

          To keep the lids light and simple, we use a short whip with a valve in it, but a more elaborate set up would include a cross, with a exhaust, a filtered makeup, and a pressure gauge.


    • It works through the lid if it the lid is thick enough, it is just less strong than through the wrapper. We do that on the Mk I, II, and III purging lids.


  37. Posted by Marc on August 2, 2013 at 6:00 PM

    I would love to get some help with the heat tape.

    I got some from a local reptile store. Tried it both plugging directly into the wall (to test temp) and with a store bought dimmer. I could get it to 105 or so, but as soon as the cool metal pot hits it, the temp drops and it doesn’t have the power to bring it back up.

    Could it be that I should wire my own dimmer. If so, could I please have some help with that?

    I also tried getting the vacuum pot to the desired temp with another heat source and using the tape to keep it there and that wouldn’t work either.

    Thank you in advance or your help with this, and for all the other resources you have given us.



  38. Posted by cary on August 1, 2013 at 6:30 PM

    I am looking into purchasing some new tech. If I were using a 20 inch diameter pot,
    should I use acrylic or polycarbonate. I have found up to 2 inch poly carbonate.


  39. Posted by G on July 27, 2013 at 1:12 PM

    Curious about Steves Acrylic box. I was under the impression that you were not in favor of acrylic and wanted 1 1/2 inch polycarbonate. is 1 1/2 inch really necessary? thats awefully thick and hard to source. i was thinking of using 1/2 or 1″ polycarbonate….which i imagine would suffice is you think a 1″ (im assuming, but it could be thicker) acrylic box is sturdy enough for repeated use


    • It depends on the size of your box. Acrylic is actually stiffer than Polycarbonate, just not as strong. Young’s Modulus of Elasticity (E) is 3.2 for Acrylic and 2.6 for Poly Carbonate. To put that in perspective, glass is 60/90, aluminum 69, and steel 200.

      The low modulus of elasticity number tells us that it will deflect a great deal under pressure and the way to reduce the deflection, is to make the panel and pot smaller or to make it thicker in the direction it is flexing.

      What I found on a 12″ pot, was that 1″ of Acrylic still deflected noticeably even cold and went to the thicker panel to keep deflection close to nil. Consider that heating rapidly reduces the strength of the plastics, which is why the cheaper vacuum chambers with thin tops warn against using heat.

      Continuing to flex can cause the panel to fail through high cyclic fatigue, which is what is regularly happening to vacuum chambers using thinner lids.


  40. Posted by Tony on June 16, 2013 at 2:07 PM

    Hey there GW, I was hoping to get some help on setting up. I have a vac pump, manifold gauge set and a vacuum dessicator..but I can’t figure what type of stuff I need to connect them all, as far as valves or additional tubing. Obviously I can connect the manifold gauge set to the vac with one of the hoses (yellow according to the manual)..but I’m stumped on how connect the gauge to the stopcock of the dessicator and back to the pump. It seems like 2 different types of tubing would be needed. Any info would greatly be appreciated..thanks


    • You can either install a 1/4″ flare fitting so that it matches the same hose as your pump and gauge, or install a hose barb on both ends and install another heavy wall hose suitable for vacuum service. On my desiccator, I cut a vacuum hose in half, and used the flare female connection on one end, and stuck a barb in the other end.


      • Posted by Tony on June 17, 2013 at 1:45 PM

        Thank you very much for the swift and informative response. Just to clarify so I don’t confuse myself..the manifold gauge I have has the blue, red and yellow hoses. I would be hooking up the yellow one to the vac, and then hook up one of the other hoses to the low side of gauge since that’s the one that has the Hg reading? And hook the other end of that up to the dessicator using one of the ways you described? And finally, lol, I would keep the high side of the manifold gauge closed since it won’t be in use and/or needed? Sorry..just tomorrows the big day and don’t wanna have to use the dreaded brake bleeder lol


        • Posted by Tony on June 17, 2013 at 2:29 PM

          While I’m awaiting moderation why don’t I sneak another one in to save on response time. The hose on the break bleeder I have fits on the stopcock no problem. What’s your opinion on cutting that hose off, and either: getting a hose barb that will connect to one of the manifold gauge hoses and then connect that to the other hose and then the dessicator. Or cutting the end of the manifold hose off as well and getting a double ended hose barb to connect the two. This is all assuming that cutting the end of the manifold hose off and just putting that right on the stopcock with maybe a hose clamp for insurance is not an option? Thanks again, can’t tell ya how much I appreciate it (but I’m tryin! Lol)


          • I would put either two tees or one cross in the line from the chamber. One port for the gauge, one port for the back fill valve, and the last for the ball valve isolating the vacuum pump.

            The gauge you have will work, as will the hoses, if you use the right fittings. You just have to maintain about 15 psi negative pressure without leaking.

        • We don’t use an AC manifold set, just a gauge and two ball valves.

          One to isolate the pump from the chamber, and the other to back fill the chamber with outside air.


          • Posted by Tony on June 19, 2013 at 6:21 PM

            Cool, thanks again..I’ll have to try to tweak the setup once I get a little more familiar with it maybe. I definitely would like a bigger gauge to read the smaller increments. We couldn’t find a hose barb with the same threading as the manifold hoses, we cut one end off to bring with us on our search. So we felt that a pretty good alternative was a double ended hose barb to connect the brake pump hose to the manifold hose. Fast forward 24hours…it worked great!Next I gotta get into winterizing, I really want to be able to see through it. Couldn’t have done it without ya, didn’t even know what a hose barb was til your first response, lol. Thanks for everything and providing a great site thats easy to comprehend. If I may ask, is your avatar pic(of the dogs) on the forums a real one? If not I’ll pretend it is lol

          • Pleased that it worked out for you!

            No, I found that avatar picture on the internet and fell in love with it. A lot of subtle messages in it to me, saying that our differences complement one another and together we can see afar.

  41. Posted by Frank on June 10, 2013 at 9:22 AM

    Thank you so much for this, I will be taking up the heating pad portion of the build next.

    I have mixed feelings about scraping to unbleached parchment or teflon, as I hear particles can become mixed with the essential oils.

    Now that I have the ability to place my entire pyrex spray dish into the vacuum chamber would you see any disadvantage to vacuuming on the dish and then scraping onto an oil slick or into a jar for storage?


  42. Posted by Dubologist on June 5, 2013 at 8:26 PM

    How do you heat the purge through the acrylic vac chamber? Same way as with the SS?


  43. Posted by ron norman on May 14, 2013 at 11:22 AM

    That 1-1/2″ polycarbonate is pricey as you say, I have a lot of 1/4″ and am wondering if laminating that together like plywood would work well for strength? Some of the binders are very strong.


    • The 1 1/2″ Polycarbonate bank window was laminated out of two 1″ sheets, capped on both outsides by a 1/4″ piece. You might contact Multi Crafts Plastics and ask them how they do it. However they did it, left it perfectly clear.


  44. Posted by San Diablo on April 21, 2013 at 10:35 AM

    Good call Hamilton Foro!! That was the first thing i did when i got my chamber set up because i read about the oil siphoning into the chamber. i also use quick release connections so i can 1. close the valve sealing the vacuum & disconnect the pump from the chamber 2. easily able to release vacuum with fresh air and then repeat process until product desired


  45. Posted by Dr teeth on April 20, 2013 at 12:27 PM

    I really advise against using an acrylic lid if you’re going to be purging any alcohols off. I’ve have 3/8″ and 1/2″ lids implode upon me. Here is just one of many examples:

    I have since been using a 1/2″ aluminum plate.


    • I would expect a 1/2″ acrylic lid to eventually implode from high cyclic fatigue and heat, which is why I specified a 1″ lid that doesn’t deflect so far under pressure. I would have used a 1 1/2″ lid, but they didn’t have any in stock.

      I prefer 1 1/2″ Polycarbonate, and that is what I have now procured for long term use. I will post updates when we build those units.


  46. Posted by Kgb on April 18, 2013 at 10:49 AM

    Its beeeeeautifulll!


  47. Thank heavens you put a valve on the pump side! I see so many people leave the pump side exposed to the vacuum pressure when you shut it off and the seals will eventually die and shoot pump oil back into your chamber! Definitely need the valve on the pump side like you have! (in addition to the release valve as well).


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