Introduction: Propane Tank to Air Storage

Picture of Propane Tank to Air Storage

Since my air compressor is only 2 Gallons, and im to cheep to buy a bigger one, i converted an old propane tank into a air tank.

BUILD AT YOUR OWN RISK!

COMPRESSED AIR IS VERY DANGEROUS AND SO IS PROPANE

NOT MY FAULT IF YOU BLOW YOURSELF UP

Step 1: Parts

Picture of Parts

This is my first instructable and writing is not my strongest subject.

Sorry for the bad/lack of pictures, i built this in under 10 minutes and only though about making an instructable after i was half done.

The parts i used were:

  • 3/4" to 1/2" adapter
  • 2, 1/2" male to male adapter
  • 1/2" shutoff valve
  • 1/2" T (this is only 1/2" because Rona didn't have 1/4" T's)
  • 2, 1/2" to 1/4" adapter
  • 100 PSI pressure gauge (can be higher but i didn't want to buy a 200 PSI gauge since im not going to be using this over 100 PSI)
  • 1/4" air male adapter disconnect

Step 2: Putting It Together Step 1

Picture of Putting It Together Step 1

Install 3/4" to 1/2" adaptor

Step 3: Putting It Together Step 2

Picture of Putting It Together Step 2

Install 1/2" male to male adaptor

Step 4: Putting It Together Step 3

Picture of Putting It Together Step 3

Install 1/2" shutoff valve

Step 5: Putting It Together Step 4

Picture of Putting It Together Step 4

Install other 1/2" male to male adaptor

Step 6: Putting It Together Step 5

Picture of Putting It Together Step 5

Install 1/2" T

Step 7: Putting It Together Step 6

Picture of Putting It Together Step 6

Install 2 1/2" to 1/4" adapters on T

Step 8: Putting It Together Step 7

Picture of Putting It Together Step 7

Install air hose disconnect

Step 9: Putting It Together Step 8

Picture of Putting It Together Step 8

Install PSI gauge

Step 10: Fill/Pressure Test

Picture of Fill/Pressure Test

I recommend that you pressure test your tank first but since i only have a compressor that goes up to 100 PSI and the tank will never be filled more than 95-100 PSI i kinda skipped the pressure testing.

Step 11: Conclusion

Picture of Conclusion

I made this tank to expand my 2 gallon air compressor to about 6 (4+Gallons in a 20LB tank) Im not taking this tank with me anywhere nor am i using it as a air pig. With that in mind i think it turned out pretty good. The tank was laying around at the farm and i needed a bigger compressor but i didn't want to drop $200 on a big compressor. I spent $40 on this, $20 for the air hose and adapters (It was a kit), $10 for the gauge,and $10 for the pipe's.I gave it a very quick paint job with some spray paint to cover up the rust and its ready to use.

Thanks for reading sorry if what i wrote made no sense or was jumbled up.

Please comment or like (what ever you do on this site, im new here)

Thanks

Matthew

Comments

O-Budd-1 (author)2014-11-14

Propane tanks are very useful for portable air tanks, BUT they must be ventilated or otherwise cleaned of ANY residual propane.

It was explosions caused by tanks with residual propane that has caused the conversion kits to be removed from the market. Explosions that I've heard caused deaths.

Here's some ways to clean the gas out:

1) allow your air hose to blow into the tank after removing the propane fittings for 30 minutes.

2) fill the tank to overflowing with water then drain.

3) pour 1 liter (or quart) of vinegar into the tank then add 1 small box of Baking Soda (not baking powder!) to generate Carbon Dioxide gas to displace the propane

Be Safe!!!!!

Budd

noahspurrier (author)O-Budd-12014-11-20

This seems overkill. If the tank is vented to atmospheric pressure and the cylinder wall temperature is room temperature then there cannot be enough remaining propane gas in a 20 pound tank to amount to more than a pop if you deliberately lit it. On the other hand, the ethyl mercaptan which is added to make propane smell bad is itself highly flammable and the vapors explosive. This residue lingers for a long time even in a vented cylinder. I'm not sure how much damage this could cause.

stoobers (author)noahspurrier2014-11-20

This "vented to atmosphere" shouldn't be considered adequate for purging a tank of propane. A mixture of propane and atmosphere (oxygen/nitrogen) can burn if there is around 10% to 25% propane gas. It will burn very fast and explosively. Above this level and there isn't enough oxygen to support a flame - test carefully! Below 10% and there isn't enough gas to reliably light. Again, if you want to test it, test safely.

noahspurrier (author)stoobers2016-10-30

I should have noted that the tank must be both vented to atmosphere and be at ambient temperature. If you accidentally vent a full tank of propane it will spray propane at moderate pressure for a period of time. Slowly the pressure will drop until the propane comes sputtering out at very low pressure. Someone might inadvertently think the tank is near empty, but it could still be near full of liquid propane at atmospheric pressure. You would notice that the sides of the canister will be wet or frozen with condensation. The tank will be very cold. What happens is that the pressure drop causes the liquid propane to boil off as a gas. This cools the propane. The propane temperature also drops due to adiabatic cooling. I'm not sure if the temperature drop is mostly due to the boiling or due to the adiabatic cooling. I think it's mostly adiabatic. As the propane temperature drops the pressure at which it is a liquid drops. In other words, at atmospheric pressure the propane can easily remain a liquid as long as it's cold enough. Looking at a phase diagram for propane it looks like this is -44 degrees fahrenheit. So obviously you could only be sure no propane is left if the tank warms up to ambient temperature -- assuming your ambient temperature is over -44 degrees (so don't try this in Antarctica).

daniellwan (author)noahspurrier2015-01-28

my take is same with you...It's an overkill. if those guys Wanna take the few extra miles to be safe...Let them be.

You'd be amazed how much LPG penetrates the surface of the metal, the only safe way to remove all traces of the gas is to steam the interior for about an hour. When inspecting the interior of LPG road tankers we would take steam the interiors for two hours, allow to cool, gas test, then steam for another two hours. If the tankers were not inspected straight away after the second steam/cooling they always failed the gas test as the gas leached from the metal surface.

Using an old propane tank MAY be ok 99.9% of the time, but its like cutting 44 gallon drums that have only contained oil or grease - its a recipe for someone to be killed sooner or later.

My claim is that the porosity of the metal walls of a 20 pound propane tank is not sufficient to adsorb a meaningful (explosive) amount of propane.

The rules requiring the interior of purged tankers to test negative for gas can't be designed to prevent explosions at the levels you test for. My guess is that the rules were established to allow for subsequent safe operations inside the tank. Workers can easily determine if the tank had been properly purged or not simply by checking that there is absolutely no gas left inside the tank. If you are going to ask someone to crawl inside the tank and start welding in there, then you owe it to that person to be sure there is no doubt about safe conditions. Otherwise you get into this situation:

"Hey, my gas detector shows there's still gas in this tank. I'm not going in there."

"Don't worry. There's always a little gas left."

"Oh, OK. That's good because I left my flashlight in my truck so I was just going to use this book of matches for light."

It may also be that you were actually purging and testing for ethyl mercaptan. Unlike propane ethyl mercaptan is a liquid at atmospheric pressure. Lots of it likely remains inside the tanker long after the propane is gone.

Gas testers detect gas. They don't in particular detect "dangerous" or "explosive" gas conditions. They just detect gas. Most don't quantitatively measure how much gas. They give relative readings. I have a combustible gas detector sensitive to 5 ppm (in methane, but likely similar for propane). The lower explosive threshold of propane is 2.1% -- that's about 20000 parts per million. So if your gas detector is as sensitive as mine then it will alert you to the presence of gas at a level four thousand times less than the minimum explosive threshold. If I was a welder then I would trust the tank had been well and truly purged if my gas detector couldn't detect any gas at this level.

I'm not advocating against caution, but some of the precautions I've read here strike me as absurd. If a tank has been purged and left vented to the atmosphere for 24 hours then I don't see what the concern is. The residue ethyl mercaptan is more of a concern to me. I don't know of any physical or chemical process by which a significant amount of propane could have been adsorbed into the walls of the tank under pressure and then slowly released at atmospheric pressure. I am aware that metallic hydrides can store significant amounts of hydrogen, but I don't see how this would apply here. Perhaps nickel in stainless steels might pull hydrogen out of the propane molecule. The walls of the tank would have to be spongy and porous to store any significant amount of hydrogen. It's an interesting thought, but surely one would have found this phenomena described somewhere.

That leads to my final point. If this actually were an issue then shouldn't it be possible to find this phenomena described somewhere in a government safety warning, OSHA manual, ISO guideline, research report, or scientific journal abstract? While Google and the internet are not infallible, I can't find anything at all to support these claims of residual propane dangers. I would be delighted if someone can point me toward a reference to support these claims because I would find the phenomena fascinating and I would like to learn more.

One last note of caution, most valves on modern consumer propane tanks today DO NOT vent if the value is simply turned open. The valve requires that the proper hose be attached before the it will allow gas to flow. If you just open the valve and come back 24 hours later then the tank is still full of propane.

I agree that the gas does leach into the metal but what's the difference in surface area between a road tanker and a 20 Lb. bottle? In a word, significant

I also agree with the statement about oil drum cutting so I use either a cold chisel or a barrel head removal tool

Surface area is not significant, its the explosive limits of butane/propane that are critical here. You only need about 10% (varies slightly) gas to 90% air mixture inside the bottle to form an explosive mix. I know you still need a source of ignition, but that can come from all types of sources such as static electricity that comes from the small particles of oil in the compressor air. 99.9% of the time no problems, its the .1% that will kill or maim.

Surface area is not significant, its the explosive limits of butane/propane that are critical here. You only need about 10% (varies slightly) gas to 90% air mixture inside the bottle to form an explosive mix. I know you still need a source of ignition, but that can come from all types of sources such as static electricity that comes from the small particles of oil in the compressor air. 99.9% of the time no problems, its the .1% that will kill or maim.

I agree that the gas does leach into the metal but what's the difference in surface area between a road tanker and a 20 Lb. bottle? In a word, significant

I also agree with the statement about oil drum cutting so I use either a cold chisel or a barrel head removal tool

O-Budd-1 (author)noahspurrier2014-11-20

I saying "safety first, last and always".

master key (author)O-Budd-12014-11-30

Thats a bit overkill.

Just leave it upside down in the sun for a week and your good to go (for air).

The smell left behind is just mercaptin that has leeched into the steel not propane.

If you're going to cut one you should fill it with CO2 from a cars tail pipe.

matthewb241 (author)O-Budd-12014-11-14

Thanks for the advice.

I found this one at my uncle's farm with the valve off and full of water. This tank was certified in 1975 so 10 years for it to be outdated gives us 1985. The valve must have been removed sometime between 1985-2000 so it has been sitting outside for at least 14 years. All the propane smell was gone and i looked inside and their was no rust and their still is the black coating on the inside.

Once again thanks for the advice, im thinking of changing another tank into one i can take with me and ill use that method to clean out the tank.

Thanks

Matthew

DB.Cooper (author)matthewb2412014-11-21

SO,,, in a similar vein - I built one of these as a pig tank (same set up minus the valve) to improve the work of my compressor during a project. we were using nail guns on a roof outside and the compressor was cycling on and off too often.

Stunk AWFUL! ... BUT!... I WAS VERY DISAPPOINTED AT THE TIME... (I was younger then) but with all of the sparks from the nail gun firing, I truly hoped to see some flames from my guns. Not so much.

thing is - I learned later that there is more to making than air, propane, and sparks.

And yet we still continue to encourage safety in the projects we love on this site. Fires and explosions only happen when we DON'T want them to!

O-Budd-1 (author)matthewb2412014-11-14

Glad to help.

While my second son was in the Navy during Iraq Enduring Freedom, a friend of mine lost a relative there to an IED made with a propane bottle.

It's bad enough it happened in war but we don't want that to happen to someone by accident at home.

Budd

stoobers (author)O-Budd-12014-11-20

Here is another way to clear out the propane that uses chemistry as evidence it will work:

Assume the tank is 100% propane gas (it is actually lower, if you remove the valve but you can assume the worst situation of 100%).

Pressurize to 15psi with air, then vent out the gas (drops propane levels to 50%, since 15psi is an additional atmosphere of gas pressure and quantity of atmospheric gas)

Pressurize to 15psi with air, then vent out the gas (drops to to 25% propane - this is a dangerous concentration)

pressurize to 15psi with air, then vent out the gas (drops to 12%, near stoichiometric for combustion and very dangerous!)

pressurize to 15psi with air, then vent out the gas (drops to 6%, too low to go boom)

pressurize to 15spi again and it drops to 3%, which is too low to explode.

Pressurize and vent one last time just to be safe.

You then have a tank that is far below the propane concentration needed to ignite (but may still stink due to the methy mercaptain.

ElectroFrank (author)stoobers2014-11-21

One thing you may have forgotten: propane is heavier then air, so the air will tend to stay at the top of the tank, propane at the bottom. So I suggest, pressurise the tank with air, then turn it upside-down to vent, which should blow out all the remaining propane. (But I would do it twice to be sure.)

PiersA (author)stoobers2014-11-21

Very sensible serial dilution and a sure outcome.

argo76 (author)O-Budd-12014-11-20

I work in a chemical plant and to one degree or another we use all three of these methods to purge our tanks of explosive or hazardous gases. It's good advice. Releasing to atmosphere is NOT sufficient.

Viaticus (author)O-Budd-12014-11-15

All very good suggestions Budd. Do you know if brand new tanks are ever tested with propane or would they be safe? I guess it might still be worth going through these steps - one can never be too safe.

Photomancer (author)Viaticus2014-11-20

For the cost of a new propane tank, you can get new portable compressed air tanks for the same price and larger capacity (I confess I don't know the volume of a 20lb propane tank in the standard measure of gallons that compressors use - too lazy to go measure and calculate it). However, 5 & 11 gallon portable compressed air tanks, with gauges and fittings are $26 & $37. So going with a new propane tank has no cost advantage over converting and old tank as is done in this Instructable.

O-Budd-1 (author)Viaticus2014-11-15

As I understand it compressed fuel gas or compressed liquid fuel tanks ( like your Bic lighter) are flushed with an inert gas like nitrogen to displace all oxygen, but I'd flush it anyway.

Can't be too safe!

Budd

Kafukai (author)O-Budd-12014-11-14

This is what I was thinking but with the leftover gas contamination that can react with other materials. It is the same process with butane?

mrmetallica (author)2016-08-18

great job.given me a good idea.ive just picked up a compressor so once i sort it out and make sure its safe i will build one of these so i can carry it out to my car and inflate my tires .

strmrnnr (author)2016-07-17

I' ve been reacding the comments on this and l don't see any solutions to the problem - only problems.

Nice instructable by the way.

Odour - way not use somehind of a solvent to rince the tank before you seal ot up again. methanol rince ot good let it dry, laquer thinner, let it dry.

rust - since it is pretty hard (but possible) to get in there and wire brush out any rust - spray some rust nuetralizer into the tank and coat the surface and let it dry. then when completely dry try spraying some plastidip into the tank to coat and protect tje inner surface from fiture rusting.

another thing I didn't see was a quickconnect with a tire valve stem in case you have to refill the tank at the 7-11.

cheers

gizmologist (author)2014-11-27

Since I live in Arizona, easiest way to remove residual propane was open valve and let sit in sun for a few days... You'll (almost) never get rid of the stink, but the oderant isn't the propane and isn't flammable in itself.

noahspurrier (author)gizmologist2015-04-14

This is wrong. The odorant, Methanethiol (Methyl mercaptan) is highly flammable.

strmrnnr (author)noahspurrier2016-07-17

is there a solvent you can safely rince the tank with after the valve is out to get rid of the odourant? metholhydrate maybe?

joemaintenance (author)2014-12-01

a propane tank is not the proper item to use for compressed air.. unless of course you weld in a drain valve.. still, though, the tank inside, it is unable to determine how bad the rust is and as it deteriorates it can cause serious injury... probably the best thing to do is to "buy" the correct tank... Id say its NO FUN going to the E R to get shrapnel removed...

propane tanks are rated for 200psi easily, as the temperature changes, propane greatly expands and contracts causing the propane's psi to go up and down. a full tank on an extremely hot summer day could far exceed 200psi. When I built one of these, I pressure tested it at 75psi, and then at 150psi and it works fine. But as for your comment on the drain valve, yes, it SHOULD have one, but one easy solution it to turn the home made tank over 180 degrees after heavy use and drain it. Furthermore what fun is it to go to walmart and buy one, Id rather build stuff than to take the easy way out like you.

nitsujsgniddi (author)2014-12-10

I made one with 2 quick connects and put a removable air gauge that can connect to it. It also has a hose that connects to my air compressor to connect the tank as a supplemental air supply. and my retractable hose reel plugs into it as well. I did not find it necessary to put a shut off valve on it either.

dchall8 (author)2014-11-30

I have one more issue for y'all to be concerned about. I used to work in the medical research industry where we used compressed air for various reasons. The air compressor was in an unoccupied, cinder block room outside the main room where the air was used. One Monday morning there was no air. A quick investigation found the air tank had exploded and ripped up nearly everything inside the room. The steel tool cabinet adjacent to the tank was ripped wide open and contents scattered all over. It took a full 5 days to clean up the room and put it all back together. Since we were basically in the safety business, an "autopsy" was performed on the pieces of air tank. The cause of the explosion was rust inside the tank. The entire tank was rusted but near the bottom it was very bad. When you compress air you are also compressing the moisture in the air. That moisture condenses in the tank and just sits at the bottom. We had had issues with wet compressed air damaging some of our equipment, so we ended up replacing the tank with a new one (duh!) but we put dryers on the compressor itself. The compressed moisture was taken out before the air entered the tank.

Side note: the farmers where I live use propane to inflate their car tires if they run low out in the country.

joemaintenance (author)2014-11-26

you could build this simple tank OR you can go buy a portable air tank from any home improvement or hardware store.. why build it???

It was cheaper to build this one then to buy one and buying one is no fun.

Thanks

Matthew

joemaintenance (author)2014-11-26

you could build this simple tank OR you can go buy a portable air tank from any home improvement or hardware store.. why build it???

garyacrowellsr (author)2014-11-21

Any reason a propane tank couldn't be used as a vacuum tank? I was thinking it might work for a plastic vacuum forming system.

it could, but in order to get your items inside; you'll want to do a few things.

1.) split the tank in the middle where the welding seam is with a grinder. (caution: depressure the tank)
2.) weld a lip to both halves
3.) get a sheet of rubber and make a gasket that will lay between both lips.
4.) optional: build a drop in shelf and make it level, with or without additional shelves.

once done you'll be able to drop on the top half, vacuum the air to the mercury you need. best thing about a vacuum chamber, you really dont need anything to join the two halves since the vacuum holds them together. Provided you've got both lips flush.

Jollyriffic (author)Jollyriffic2014-11-25

as already stated here, and comes with any tank containing flammables. makes sure to remove any lingering gas before splitting the tank. just read below for the multitude of ways in how to do so..

n1cod3mus (author)2014-11-25

this might help me out, I want to hold a vacuum in a tank, not a bad idea to upcycle a tank.

ronaldvskinner (author)2014-11-22

I have one of those cigarette lighter air pumps that the hose broke off of, I should rig one of these up and see if that little sucker won't hide in the handle / valve protector and have a rechargeable air pig. My only thought is that if you are using it as an air pig, perhaps figuring out how to keep the fittings within the protection of the handle might make it more durable.

It would fit within the handle if it wasn't for the shutoff valve.

Thanks

Matthew

ronaldvskinner (author)2014-11-22

I think you underestimate the value of your contribution. I observe some pretty impressive layouts on this site, obviously some talented people. Maybe you don't feel this is as polished as some of the others, but you have an excellent idea and I appreciate you shared it. The comments section is were the group can help polish it up with info if it's necessary. I look forward to your next idea cause it's obvious you have your own genius going on...

Thanks

mreitan sr. (author)2014-11-22

Nice job Matt for your first time.

matthewb241 (author)mreitan sr.2014-11-22

Thanks

theNightwalker247 (author)2014-11-15

Don't get me wrong.But couldn't you put a cross outlet instead of a T outlet on it so you could have continues air pressure.

Could the T fitting be turned 90 degrees and a small pressure gauge be used such that it stays below the "handle" as a guard, and the valve be horizontal, etc. The gauge would read the pressure all the time.

matthewb241 (author)dpridge2014-11-21

I tried that but the gauge was still over the guard, and i think this way looks better

Thanks

Matthew

-A-N-D-Y- (author)2014-11-20

Just remember to drain it every so often as it will collect water the same as your main tank :)

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