Air Can From Empty Refrigerant Can





Introduction: Air Can From Empty Refrigerant Can

About: Tim Anderson is the author of the "Heirloom Technology" column in Make Magazine. He is co-founder of, manufacturers of "3D Printer" output devices. His detailed drawings of traditional Pacific...

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

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

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.



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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.)

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)

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".


1 reply

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.

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?

1 reply

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).

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

1 reply

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.

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.

1 reply

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.

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

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!

8 replies

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.

fill the tank with water and empty it out

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

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


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.

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.


Or you could get a pressure shut off valve ;)