bho - large scale closed system


Well-known member
Hi - this was posted on Overgrow and I've had many requests for information on it. This is my closed system for bho extractions. I hope you like it. Of course, a few safety thoughts -

Please don't berate me with "thats gonna blow up". Yes it might, and if you can't make a judgement for yourself about how safe this is, then you don't even need to consider doing it for youself. I personally think it is safe if done as I describe, and certainly outdoors, safety glasses on, fire extinguisher available. So if you think this is too dangerous, then in your hands it is.

I have done about 8 runs, and have made some modifcations over time, so some of the pics are from earlier runs, Ill try to comment on the changes, mostly my oil is now clearer than the early pics (shorter steep time and maybe even precool the butane using the recovery pump), and Ive omitted the filters and dryers cause I dont find it matters.

I know of one other functioning system and 2 more that are being built. Ill try to answer questions if you get really serious about this, but I hope its all here, and if you cant figure some of it out and improvise, then you shouldn't probably be doing it anyways.


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First, I filled the pressure vessel with about half of this cannabis. You should be able to fill it about 3/4 and still work. your liquid level sight will need to be higher than your highest level you intend to fill with. You will be using a 2.5 gallon aluminum paint pressure pot. The cannabis should be overly dry, I put "dry rite" dessicant in the bag with it to make it totally too dry, and leave it a week, not sure how essnetial. The lid has a stainless tube that goes to the bottom, into the stainless screen/filter that you see here. you can get screen filters for the paint tube at the paint supply place that you get the pressure pot. The stainless inner lid just keeps the cannabis from floating, you can use aluminum flashing cut so it sort of binds up. If you are filling your vessel, it doesnt really matter if it floated, but probably better to keep it down. This vessel I call the "steep" vessel. It requires some method to determine the butane level, and I have rigged a clearish teflon tube to provide an indication of the level. The better way is the liquid level listed in the parts list, I didnt find that till after I rigged the clear tube onto mine. I cant think of a safe way to do it without some method of determining the butane level in this pot.

some details -

pressure pots generally have 4 ports in the lid.

1) one port leads to a stainless tube that goes to the bottom of the pot. this is the tube you will transfer the liquid butane through, initially to fill the pot, and after a 15 minute steep, to transfer the butane/hashoil to the second pressure pot where you will do the evaporation stage. this port normally connects to the paint hose by whats called an inverted flair adapter. it is industry standard for pressure painting. you will need 2 of these fittings, best to get the type that can be removed from the tube (usually using an allen wrench) and this fitting will be silver soldered or welded onto a 1/4" flair adapter male, then you will be able to connect a refrigerant line (these lines all have female 1/4" flare hand twist fittings on both ends) . one could also just weld a 1/4" flare male fitting (home depot/or ace) to the fitting on the pot, but I wouldnt.

2) another port goes to the air pressure and typically through a regulator that comes with the pot. remove the regulator and fittings and depending on the pot, you will be left probably with a 3/8" npt, thats national pipe flair. There are on the shelf adapters for npt to flare. use rectorseal yellow pipe dope, much better than teflon tape.

3) one pressure release valve. probably best to a small circle of neoprene rubber (1/8" thick) and make a more sure seal between the stainless ball/spring and the seat, this will retain the safety benefits of the relief valve, but eliminate the small leak inherent in them.

4) a twist relief valve. this stays as is and is used to check if all pressure is out/ vacuum ect.



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Now, we put the lid on it and fill it with very very clean butane. The teflon tube lets me know when the cannabis is covered, you will likely be viewing the liquid level gage listed in the parts list. Im using the refrigerant recovery pump to expedite the transfer, using what is called a push pull technique, routinely used in refrigeration work. The tank is called a recovery tank and is special ($70) It has two ports, one leads to the bottom (liquid) and one the top (vapor).Once filled the cannabis is allowed to "steep" for some period of time. I have yet to decide how long is best, this run I steeped for 1 hour, probably too long. The oil I got on this demo run was a bit dark. I would steep for 10 minutes or so the first run, get a lower yeild clearer oil, and then do a second run with the same pot, but steep perhaps an hour.

I got this refrigerant recovery pump at a local pawn shop for $100, it wasn’t working. I bought a refurb kit for it for $150 and spent several hours fixing, taking apart, and cleaning it. Works like new now for $250. These pumps are on ebay both new/used/and refurbished, but if you get a used one, expect to take it apart and clean it out and I would put in a refurb kit. These pumps are made so that it is easy to refurb/clean/disassemble, it’s common maintenance for them.

Some details, its not as complicated as it looks, im not good at being concise.--

on each of the two ports of each vessel, I have put a ball valve that is part of a short 3 inch hose, listed in parts list. this is your valve for each port and has the fittings built on. so you need 4 of them, they come 3 to a set so you have to buy 6 from grainger, 2 spares

before putting butane in the steep vessel, you pull a hard vacuum on it. this all doesnt work as well if there is air in the system. you hook the suction port of the pump to the vapor port of the steep vessel, hook a hose to the liquid port of the tank and connect to the liquid port of the steep vessel, leave the tank valve closed but open both ball valves, pull a vacuum till the gage on the pump shows a good vacuum, this evacuates both hoses and the vessel, close the ball valve on the steep vessel. the pumps output is just to the environment for pulling air vacuums.

the "push pull" technique is used to move the liquid butane. The suction port of the pump is still on the vapor port of the "steep vessel" , the liquid port of the steep vessel is still on the liquid port of the tank. put a hose on the output of the pump, but dont hook it up to the tank yet, it will hook to the vapor port of the tank. open ball valve on liquid port of vessel, then open the liquid valve on the tank. the vacuum in the vessel will pull some liquid butane into the vessel. it will equilibrate in 2 minutes or so. then turn the pump on, briefly and slowly open the ball valve to the vapor port of the vessel that is hooked to the suction port of the pump and you can also manipulate the valve on the pump that opens the suction. some butane will be pulled throught he pump, and displace the air that is in the pump and in the pumps condenser, you will see some butane come out of the hose that is hooked to the output port of the pump, then shut the ballvalve that is connected to the vapor port of the vessel. now you have displaced the air, and can hook hook the free hose up to the vapor port of the tank,

you can leave the pump running, but it will shut itself off if it overpressures.

so now you end up, pump on, all valves open, and very quickly the vessel will fill with liquid butane, you must turn things off when the liquid level is where you want, basically filling the vessel 75% or so, or just over the top of the cannabis.

shut all valves for now, and steep 10 minutes first run, one hour second run. (edit add- I steep 1 minute first run 3 minutes second run now and get almost as much oil out and its lighter in color)


the blue knob on the pump opens the suction port. this leads to the vapor port of the steep vessel, a 3 foot hose to a short hose/ballvalve assemble.

the red knob on the pump is the output to the recovery tank vapor port.

the red knob on the tank is the liquid port, in this picture, I have put a filter/dryer inline. I dont know if this is needed, but it is listed in the parts, this filter dryer has short ends that can accept a 3/8 inch compression fitting, that i had to end up putting to 3/8 copper and then soldering (rigging nonstandard) the male flare fittings. room to adapt here. in refrigeration you get a slow buildup of water and it screws things up, so Im going to dry it with each run this way.

the center knob on the pump is the purge knob. when completed with certain steps, you turn this knob to purge, it puts the internal condenser on the suction side of the pump, but for vapor recovery it is on the pressure side. by putting it on the suction side, you can get all the liquid butane out of the condenser and put it in the tank when you are through. Important and in the pump instructions anyway.



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The butane/hash oil mix is transferred into a second pressure vessel, called the evaporation vessel (transfer not shown). basically this is the same as going from the tank to the steep vessel, but for this phase, the steep vessel is put into the circuit just like the tank was to fill the steep vessel, and the evaporation vessel is put in the circuit just like the steep vessel was.

once all of the butane is transferred, it wont take long, you close all the stopcocks. watch the pressure output on the pump, the vessels shouldnt be run over 100psi when they are on the pressure side (only for the vessel to vessel transfer), but the tank can run up to 450, and there is an auto cutoff at that pressure anyway.

The evaporation vessel does not need a liquid level sight. If this were an aluminum vessel (that’s what’s most available) I would consider putting a stainless or glass vessel (mixing bowl?) inside of this to catch the butane and eventually contain the oil. With my vessel, I'll just let the oil form on the bottom of the vessel.

now, the vapor port of the steep vessel is shut off once the transfer is made. the liquid port of the steep vessel is connected to the liquid port of the evap vessel already, as for the transfer. I may cut that red hose (the red lets me know I have used this hose to transver butan/oil mix. you dont want any hash oil residue to ever get in the pump.) and i might put a 3/8" ( ti think it will fit) or perhaps 1/4" fuel filter with hose clamps in this hose, havent yet.

anyway, now you hook the vapor port of the evaporation vessel to the suction port of the pump, leave the output hose of the pump free, we are gonna displace a little air again before we hook it to the vapor port of the tank.

run the pump, open the valves between the vessels, and the valve between the evap vessel and the pump, then the pump vacuum knob then close when some butane comes out of the output hose, then hook it to the vapor port of the tank, then turn it on, and open everything, and the evaporation will begin. It might take several hours to evap all the butane from the evap vessel, and the suction will also get any butane stuck in the cannabis, and the hose/?filter between the vessels. you will know you have all the liquid out when the gage on the suction side reads a vacuum. vacuum for at least another hour or more to purge the butane out of the oil.

This picture shows the refrigerant recovery pump removing the vapor phase butane from the system. The "steep" vessel with the cannabis and the evaporation vessel are connected and valves open, this gets all of the butane out of the sytem. It took about 1.5 hours to reach a vacuum (probably 3 liter butane this run), then I kept it at a hard vacuum for another hour to purge. It needs more purging than this probably.

The evaporation vessel gets cold from the evaporating butane. Things speed up if you put it in a bucket of water to warm it.

edit 5/29/12 I was asked to clarify any changes in the procedure by PM and this was my answer
I would do two things.

buy a clear fuel filter. they are common at auto parts stores. cut one of your hoses and put it in the middle with hose clamps and use that hose to transfer the resin containing butane from the steep pot to the evaporation pot. You will be able to see when it finishes transferring.

now, I dont do hose transfers like my tutorial shows.

hose from liquid line in storage tank to the steep pot, the port that runs to the bottom.
hose from the top port, vapor port of the steep pot, to the liquid port, runs to bottom, of the evap pot.
hose from vapor port, top only port, of the evap pot to the suction of the transfer pump
hose from the output of the pump to the holding tank.

you can leave it like this for most all of the run.

so you pull a vacuum on the whole system with the holding tank valves shut off and the hose from the output of the pump cracked so that the air can vent.

turn everything off and then open the liquid valve on the tank. watch your level and if you need to, turn on the pump to tranfer enough to fill the steep pot about 80%, when you smell some butane come out of the hose that goes from the pump output to the tank vapor, tighten the hose fitting and open the holding tank vapor valve.

when the steep pot is full. shut off the liquid valve on the holding tank, and also the little valve at the steep pot end of that hose if you have one.

once the steep time is over, I go about 30 seconds on first run and a couple of minutes on a second run and I keep the final products seperate. I sort of swirl the pot as it steeps. when the steep time is over, turn the pump on in its recover mode, as always. turn the steep pot upside down, and now the suctioning vapor port will be at the bottom, no hose changes needed. watch the butane suck through the tube that connects the steep pot to the evap pot, you can now watch it through the clear fuel filter. Ive never had a problem with it leaking or worrying about the pressure. when it completes the transfer, you turn the steep pot back upright, open the valve on the hose that connects the liquid port of the tank to the steep pot, but not the liquid valve onthe tank, this is to get any butane out of this line.

then just let it run until you can pull a good vacuum bases on the pressure gauge on the pump.

I put the holding tank in ice now and the evap pot in just outdoor temp water in a big tub. it speeds it up a great deal.



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once you have a vacuum for a while, you turn the pump off, and turn the purge knob on the pump to purge, and turn the knob to the vacuum port off, then start it back up. it will take a short while to show a vacuum again as it gets the residual liquid out of the condenser and puts it in the recovery tank. once it reaches a vacuum. close the tank valve, and you are through.

recover your oil, and repeat, but this time steep for an hour or so to get the last oil out. may even be good to do 3 runs, I dont know yet.

oil in little teflon© bags.

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Well-known member
summarized shopping list for your new expensive toy

2 packs of these, you really only need 4 valves but they come packed in 3's

3 hoses, make sure that at least one is a different color, or mark. Keep the ones used for clean butane seperate from the one that transferes the oil containing butane.

this replaces the welded and adapter/tubing tangled thing I used to check the level in my pictures. You will likely need to make another gasket on the outside, the one it comes with (oring) is made for a flat surface, and you need a thicker gasket, in addition to the oring it comes with, so it will contour to the outside curve of one of your paint pots. Mount this as high as you can on the pot without it interfereng with the lid being tightened, and allow for some temperature expansion/contraction.

a "recovery tank" and the fill sensor that goes with it. I skipped the fill sensor, but if you do, you have to weigh the tank (instructions for weighing come with tank) to be sure you dont overfill it, or it will explode. the overfill sensor interfaces with the pump to shut it down if you overfillit. only really needed when you intially fill the tank with butane. 30 lb tank - or maybe better since you guys have 2.5 gallon paint pots to get the 50 lb tank -

and the sensor -

one gallon of butane per case, get several while you are at it - multiple places

can tapper - http://{keyword}&gclid=CPWEt7WT0rUCFQjNnAodcT0A-A

and of course a oiless recovery pump, either freshly refurbished or new (refurbished on ebay is much cheaper and should be just fine)

and 2 2.5 gallon paint pots, sometimes on ebay - or new -


if not grainger, then most can be found here online - tank shop around, these guys are 2x graingers price


Foaf,Excelent job as usual,I read your closed system thread on OG and I am still impressed.Did I miss where You get the huge tank of Butane? :wave:


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thats an amazing extraction methode. great job makeing it work. did you posses the basic knowlege before you started this project? its been a long time hope of mine to find someone with a closed exraction system. i love the idea of reuesing the butane. how much did the whole setup end up costing if i may know. also how long does it take to make the first batch and what are the oil yields like weight wise? thanks for shareing K+


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thanks gaiusmarius

I have a chemistry background, and can do simple welding and generally a capable handyman, but I didnt have any hvac background. the whole setup is just about $1200. My pots are one gallon, but they are special and basically you cant get them. the standard size is 1 quart (not worth the trouble) and 2.5 gallon (most likely), the one gallon pot takes about 2 hours to finish and tack on a hour or more for a vaccum purge and the end. That time is mostly spent just with the pump running, its made to run like that. Only about 5 minutes total intervetion time, switching valves and loading and unloading, ect. The yeild, I had recorded the numbers on OG, and honestly I forget, I havent done it in several months, but am about to. The yeild was comparable to the blow through methods.
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Just been looking at refurbished recovery units, and found some at reasonable prices. None available locally sadly. Damn.
This looks like a great future project though, and I had a job at an LPG depot when I was a teen, so it shouldn't be too much hassle to set up. Just sourcing the parts will be difficult.
Thanks for posting this foaf, it is really helpful.


man this is an awsome idea, i love the way you recolect the butane after each run. how many times can the butane be used? i have a few bags of trim just waiting to go in there man, lol. could you tell me more about the vacume purge? is it more efficient then the normal hot water purge? would you say you got all the butane out of the end product?

i would love to learn how its done. what do you think is the best substance to extract with.