Introduction: Air Can From Empty Refrigerant Can

Picture of Air Can From Empty Refrigerant Can

Nice for filling up air mattresses, bike tires, blowing dust out of your computer, etc etc. This is a useful thing to have.
If you ever get your car stuck in soft sand, snow, or mud, there's an easy way to get out. Just let air out of your tires til they're at about 10 or 15 psi. They'll have a nice big flat spot on the bottom, won't sink in nearly as much, and you'll drive right out. The military think this is such a useful trick that many military vehicles are equipped with gadgets that can drain and fill the tires from inside the cab. On Cape Cod there are still some beaches you're allowed to drive on. At the entrance to one such beach is a shed with an air compressor and a sign telling you why to flatten your tires a bit.
Without such a convenience but with a couple 100psi tanks of air in your trunk, you can refill your tires quickly after you're done driving on the beach.

Step 1: The Plumbing

Get an empty freon can from behind a garage or air conditioning contractor.
They will have pumped out all but a few molecules of nasty gas using trade school magic.
Make sure it's a really empty one by using your own brain.
Otherwise teenage nerds will heavily criticize these instructions.

Get your fittings and put them all together. You'll probably have your own scheme in mind which will be different from mine.
Wrap the threaded parts with teflon tape before assembling to seal the threads. If you don't have teflon tape use a strip from a plastic shopping bag.
Attach your hose to the tank with a hose clamp.

Step 2: Defeating the Check Valve

Picture of Defeating the Check Valve

This can had a check valve. When I tried to fill it no air went into the tank, even with the valve fully open.
To take the valve apart I had to grind through the lip around the edge with a dremel tool. Then I unscrewed the knob til it came off. Inside the valve body was a ball bearing and spring. that was the check valve. I pulled them out and reassembled the valve. Now I could fill the tank.
Two views of the top of the valve with the ground-off lip shown.

Step 3: The Attachments

Picture of The Attachments

The hose coming in from the right comes from my air compressor. To fill my tank I use the double-ended nipple dingus in the middle. If you're filling your can at a gas station cut the stem off a bike innertube and either tee it into the airhose to your tank or hose-clamp it to a quickrelease nipple. The other two dingii in this picture are a blowgun and a tire filling attachment. I like the quick release stuff because I already have it and it makes experimenting quick.


JillW34 (author)2016-07-10

If you are going to cut a gas tank propane or gasoline fill with water. I.have heard of.people welding gas tanks.only when.they were full.of gas. I dont get the logic on that but what my welder says. (Old school welder, only one I know that is great at welding things others cant.)

wfidrock (author)2015-06-01

The real danger in using disposable freon cylinders for this is that they are not only thin-walled BUT ALSO unpainted on the inside (bare steel).

In normal use there is ZERO moisture inside until all the freon has been exhausted (and without oxygen and moisture, no rust).

Once you start refilling with a compressor (from the atmosphere) you are introducing both oxygen and moisture (humidity) and the inside will begin to rust. Over time this rust ill cause a failure of the tank, hopefully not catastrophic (most of the time it will just begin to leak, but i can / could explode instead).

Just play it safe and buy a 5 gallon portable air tank for under $30 at a place like Harbor Freight Tools (you get a tank, a gauge and a hose for a very reasonable price).

-Walter (EPA 608 Certified Technician)

Tegra (author)2013-06-25

With all due respect.....

It is true that it is illegal to "Transport" refilled cylinders. However, what does transport mean? This means moving, usually in large quantity, from one place to another, for someone else, for a price.

When I bring groceries home or take my gear on a camping trip I am not engaging in "Transport".

It has been explained to me that it is perfectly legal for me to take a refilled cylinder in my vehicle. It may be another thing if something went horribly wrong on the way and the insurance company hired a layer or two.

As far as the cylinders, these are similar to the "Balloon Time" cylinders. How much pressure do they contain, sitting in the isle at Walmart and bouncing around in the hot car on the way home/to a party? Approx 250 PSI!

To refill one with compressed air at 125 PSI and stored in a safe place seem very reasonable to me.

Ones point to the YouTube videos (and the shop teachers scare tactics) that show a high pressure cylinder being shot at. What is the pressure in those cylinders? 3000 to 4500 PSI! Over 20 times the pressure!

What does it look like when a 125 PSI cylinder is shot? You will not see a video on this, because it is boring! Most failures will be rust induced which will usually be so slow that you will not even notice.

(If someone was to do the math they would probably find that there is not enough energy in this cylinder at 125 PSI to bend the "thin metal.

Sorry for going on like this but I get tired of "fear mongers" with their FUD.

Like I tell my kids... "do the math".


OpticHash (author)Tegra2015-04-26

With all do respect...

Transporting doesn't matter if it's one can or a thousand cans it's still transporting. Also you need to ask before grabbing these cans because they are not yours and can still be scrapped for money.

It doesn't matter if the tanks had stored over 300+psi and your now using it with 150psi. Non-refillable means it has not been heat treated and the repeated charging and discharging of the cylinder can induce stress and fracturing of the metal.

Also the law doesn't seem to clearly define what non refillable means. Does it mean you can't fill a propane tank with more propane or does it matter if your using air? I think if you get pulled over and you don't have a EPA certification you will be threatened with a $37,500 fine and a felony. Until they can prove it's air.

maxwilm76. made it! (author)2014-11-30

I decided to just cut the old valve off with a dremel cut off wheel and sweated on a new air fitting. Installed a shut-off valve, a primary gauge and a regulator. Oh and I made some custom legs for it so it would be a little more stable. I like it! I shall call her Pig-Let

browncar (author)2009-07-09

How hard is it to get a air tank used or new that you can use? I understand the need of wanting to have one . But to take risks with disabling safety features is dangerous and not worth the risk for me. Any suggestions on where to get an air tank?

Snidely70448 (author)browncar2014-08-15

Harbor Freight sells several. A 5 gallon tank rated at 125 psi, including a pressure gauge, filler valve and hose, can be bought (August, 2014) for about $25 on sale (stuff like this is almost always on sale).

coppeis (author)2010-10-11

How do you re fill it and do you think that i can re-fill it up with co2?

Snidely70448 (author)coppeis2014-08-15

CO2 as a gas is not any more dangerous than air at the same pressure. CO2 pressurized to a liquid, as it is found in powerlets (the little 8 - or - 12 gram silver tubes used in pellet guns or old paintball markers) or in the CO2 bottles sold for carbonating beverages is something else again. CO2 liquifies at room temperature at about 800 psi, but if a cylinder is overfilled and then heated pressures rise very rapidly. Throw a powerlet in a fire and it will rupture catastrophically and dangerously.

Snidely70448 (author)2014-08-15

I checked a web site for a company that makes these tanks (DOT 39). It lists the safe working pressure for their tanks as 260 psi. It does not say these tanks are tested to failure.

Snidely70448 (author)2014-08-15

OF COURSE they are disposable. That's why they are available behind a shop that pressurizes air conditioning systems. "disposable" doesn't mean useless. I just means that commercial entities cannot return them to the supplier to be refilled.

Toxictom (author)2013-08-15

I believe those transport regulations do not apply to private individuals, they are for businesses and vehicles used in commerce.

Monkeywithumbs (author)2007-11-16

Hello all! I know this is an old thread, but I have a new and relevant question and there seems to be a lot of collective knowledge on this site.
I have a small (1/5 HP) compressor that I use for airbrushing. Being that it has no tank, fine lines drawn with the brush tend to be dashed, if you will, due to the pulsing of the pump. The pump is a diaphragm type, so it's not as bad as a piston type would be, but I would like to add a tank to eliminate all skipping entirely.
My question is this: has anyone ever (or just know how to) converted a propane tank for use as a compressor tank, as opposed to a portable air tank? If so, how would one go about such a thing?
I realize that a small compressor with a tank can be bought cheaply, and if this project takes much more of my time, I will pony up the cash, but my slightly twisted mind thinks that it may be fun to make my own. Plus, I've already bought a conversion kit for a freon tank, (which, of course, are much harder to come by than propane...duh)
Thanks for any help you may be able to give!

picbuck (author)Monkeywithumbs2008-04-30

Oh my goodness. The danger is not when the tank is almost full of propane. The danger is when it's almost empty. Propane, like gasoline, burns at around a 14:1 ratio, 14 parts of air to one part of fuel vapor. You couldn't breathe such an atmosphere, but inside the propane tank you'll never know it exists...until... This 14:1 ration is exactly what you'll reach at some point if you try to pump all the propane out of the tank. At which time any spark, or even any hot spot, inside the compressor (pump) you're using will set off a horrendous explosion. Shards of propane tank flying around at very high speed. If you don't pump out the propane tank, then sooner or later the air and propane in the tank will again reach that 14:1 area. Same result. They whole thing sounds a bit risky to me.

lukeyj15 (author)picbuck2009-03-13

fill the tank with water and empty it out (author)lukeyj152011-08-03

lol, I love how simple you just owned his long comment.

lukeyj15 (author)jj.inc2011-08-04

Yup. Like a boss.

I bought a alumin propane tank at the recycling center, I opened the valve and let it set for a week I then drilled a hole in the bottom and put in a drain plug, my compresser will pump to 120 psi the tank is rated to 800 psi it's light weight and I have been useing it for over five years

Robb (author)Monkeywithumbs2007-12-30

a compressor without a tank would probably be without a pressure shut of switch, or a electric apparatus that shuts off the pump when it reaches a certain psi level, so i'm not sure it would be possible, sorry.

alexhalford (author)Robb2008-06-01

You could just stick a pressure gauge into the pipe coming out of the tank and bend the needle so that it makes an electrical connection (think Hollywood style homebrew time bomb), that activates a relay in the mains cable and switches the pump off, it wouldn't be all that difficult.

btop (author)alexhalford2008-08-03

Or you could get a pressure shut off valve ;)

alexhalford (author)btop2008-08-10

Agreed, but it wouldn't be as fun... :-)

mnmc10 (author)Monkeywithumbs2008-01-07

regarding the reservoir for your airbrush, i used a 2 liter soda bottle. punctured a small hole on the side so the thing will not be filled full. that prevents the diaphragm pump from over exerting. use fittings and hoses from fish tank supplies.

PeteBR (author)2011-07-22

My can didn't have a check valve! I should have tried filling it with air *before* cutting the top of the valve, but regretfully didn't. I took the valve apart...and didn't find anything in it.! No ball bearing or spring. So I tried filling the can....and it works ^_^

rondust (author)2009-02-09

So if common sense was applied -
1 - this is a high pressure container, way above 175psi. (over 10x 175psi)
2 - a normal compressor stores air
3 - repaint and mark as 'air only'
4 - there is exactly the same thing as sold commercially in the USA and other countries.
5 - Make sure ALL other connections to the bottle are able to handle the pressure up to 175psi.
6 - if it was illegal to transport a filled container "How do you get your LP Gas bottle home for the BBQ?" - IT'S not illegal to transport air either.
Scuba tanks are much higher pressure than this and you can leave them in the sun (not recommended for any pressurized container) as they are designed with safety factors for stupid people.

flamekiller (author)rondust2009-03-26

It isn't illegal to transport a filled container. It's illegal to transport a container filled in ways other than the intended, manufactured purpose. It's also illegal to transport refilled disposable propane cannisters. It is also, I'm pretty sure, a federal offense to disable any safety devices, including check valves and OPDs. SCUBA tanks and otther pressurized vessels are designed and engineered to be rated to a specific pressure and have wall thicknesses relative to materials used to reflect this. They're expensive for a reason and, like all pressure vessels, are required to undergo hydrostatic testing on a regular basis and be retired after so many years. Considering how cheaply purpose-designed compressor tanks can be had, illegally using a tank that once contained a noxious gas (evacuated or not) really doesn't seem worth it.

rondust (author)flamekiller2009-03-27

HHmm... "Flamekiller" work as a fireman? So it would be illegal to fill the container with a relatively inert substance like... water? or common air? (not propane). A container ENGINEERED and manufactured as a pressure vessel, designed to be refillable and designed to be filled to extreme value (about 3000psi). Well above the ordinary water tap or common air compressor (about 120 psi). In my comment, I was not talking about Industrial Gas cylinders for Acetylene or Hydrogen etc or "Disposable" gas cylinders. My response was intended to point out to LITTLE CHILDREN that the container type was very likely to easily contain those pressures of air with a very large safety factor. (By the way, probably needing a refill every 3-5 uses anyway at 120psi) We all know that kids need to be informed or an accident may occur through poor experimentation. Kids on this site are all looking to experiment - legal or illegal doesn't come into it - but they need to be safe in their methods. The point being that "YOU" could do it safely, but use low pressures, correctly label the cylinder to display clearly what is inside and its new use, and make sure that all devices or hoses are able to handle those pressures (120 psi). That there are other RETAIL available cylinders - cheap too. Lastly - if it was dangerous - I would be the first to clearly advise that the last thing they need is a high pressure container burst. I have never found connectors and gauges that have blown off my HP lines from my dive gear - luckily I've never been struck by them either. SAFETY FOR ALL FIRST - If they don't know, give them information, teach them. I apologize for offending you, if you think it is better the kids get hurt first.

kyuubiunl (author)rondust2011-04-04

D.O.T. is your problem, not common sense. Re-using and transporting these containers is illegal period. It does not pass muster as a rated pressure vessel anymore because it was MODIFIED.

rondust (author)kyuubiunl2011-04-04

I don't think you realize that the common sense side is that we are making kids aware that these containers can be filled with water or air safely, and to think about it before they do it.

Because it is illegal in any way or some way, is not going to stop them, better to get them to think about it and know it is relatively safe to do.

The original product would be filled to a much higher pressure than if it was water or air. So if the container was labeled correctly and contained the item labeled is likely to be okay.

NOT advocating filling it with LP Gas!!

Maybe you do not realize that the PET plastic Coke bottles are rated to 150+PSI
and that the average home compressor will not fill above 110 psi - so the kids could use a plastic Coke bottle as an air reserve.

But that would be wrong also under DOT wouldn't it?

Have a nice day please :-)

kricketone (author)rondust2010-07-23

Well Said

profpat (author)2010-07-09

this is very useful, i made one myself using one of my mom's spare propane(lpg tank) had to change the valve though. and its a little heavy, but since the tanks has thicker walls, chance of over charging it with air from my air compressor is nil. i have been using it for 10 years already...

stephenniall (author)2009-12-21

when i build my workshop outside im going to have a big propane canister and small electric powered compressor with a air hose into my workshop so i get to always have a air line without using up space!!

MT-LB (author)2009-12-18

There are plenty of empty propane tanks and fire extinguishers. Get one, they can be refilled safely if structurally sound. Or just get a portable air tank.

lilroud (author)2009-10-29

Im an EPA certified HVAC Tech, and these ARE one time use cans and they are suppose to be evacuated before discarding, But not required drilling. These are dangerous and illegal to use in any way other then intended. The wals on these "Virgin" R-22 containers are thinner than a "normal" container or a recovery container. The pressure in these cans brand new depend on the temperature of the can,, so they hold a threshold range of PSI but they WAY under fill them to compensate. The check valve is just to make sure no one re uses them as a extra step required by law. I mean... you could use them, like, in your own back yard, but be carful and dont get caught.

Caya (author)2006-06-26

Ok I am really really un-acquainted with these things, so I have to ask a dumb question- How do you know when the tank is full? When air refuses to go in any more? I mean, it wouldn't explode or anything, right? And I think the point about putting air into a tank with flammable remnants sounds like an excellent one- It sounds like a good idea in theory though, I guess-

static (author)Caya2009-06-08

Any air tank worthy of the name should have a safety relief valve, that should start popping off when the safe limit is approached. And scare the bejesus out of you when it goes off full bore if you don't head the early warning.

mje (author)Caya2007-03-02

You use a compressor with a pressure gauge, and stop when you hit 140psi.

trebuchet03 (author)Caya2006-06-26

(this goes for just about every tank) -- pressure will dictate when the tank is 'full'. How much pressure is the question... - but if you look on the side of the gas bottle, you might find a max pressure rating or the capacity (in lb or oz etc.) of the gas that is supposed to be in there. If you know that the tank hold X lb of gas Y -- you can figure out the rated pressure by calculating the gas' vapor pressure (at a known temp).

As for checking if there is refrigerant in the tank (including propane - which happens to be a refrigerant :P)... pour some hot water on the side of the tank. The area that remains warm is "empty" space. Areas that cool off fast have refrigerant -- a google search will give you a lot more information as to why this can be done.

As for flammable remnants.... there's only remnants if you leave them... its up to you to clean out the tank and get rid of the mercaptan (a stinky gas added for detection), which will stay behind even after LPG has been removed. This is why I say, if you let it be scary - it's gonna be scary (as with most things). - uses an emptied propane (LPG) for their air powered bike :P

Derin (author)2009-05-31

Deleting for being a stupid comment.

ReCreate (author)2009-03-16

No,Use rocket fuel

lukeyj15 (author)2009-03-13

but then you empty it out when you get home

aholgate (author)2008-10-08

How about air pressure? What does it hold? I have a 175 Lbs compressor can I put this much in it repeatedly?

aholgate (author)aholgate2008-10-08

I dare say NOT!

evanwehrer (author)2008-10-03

Where can I get a tank like that for free?

hullscrubber (author)2006-11-28

I've done something similar with a scuba tank(I always have a few with me for work) I used a tank, the first stage of a scuba regulator, and a length of tool-grade airhose. The regulator steps down the 3000 psi down to 125 psi, giving TONS of air to use for tires, air tools, etc... one word of warning, though... 125 psi+bicycle tire rated for 40 psi+me not paying attention= me crapping my pants...

John Smith (author)hullscrubber2007-08-10

Yeah, one of my relatives did that to a little kids bike, but it was fine.... ....until a little later when they heard BOOM, and saw that the tire had exploded when the kid was riding the bike.

Derin (author)John Smith2008-08-29

you must have heard the explosion from when the tire of a rubble truck went boom,the first word that i said before seeing the truck was "yikes what are they doing with the dynamite"

haha good idea

purgedsoul (author)2007-08-13

140 PSI "might" be the safe limit for these tanks but to make sure you don't go over you can check the tank for markings like this one:

DOT-39 NRC 260/325 M9701

DOT-39 - Non re-usable cylinder
260 - Service pressure
325 - Test pressure (The minimum test pressure is the maximum pressure of contents at 130 °F or 180 p.s.i.g. whichever is greater.)
M9701 - Manufacturer's registration number.

This data is for the tank that I have now which is an R-12 (yikes bad for the environment)

got these info from this page:

Derin (author)purgedsoul2008-08-29

oh no cfc yikes

About This Instructable



Bio: Tim Anderson is the author of the "Heirloom Technology" column in Make Magazine. He is co-founder of, manufacturers of "3D Printer" output ... More »
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