100 Lb Propane Tank Homemade Air Compressor





Introduction: 100 Lb Propane Tank Homemade Air Compressor

About: I am retired and have been for 13 years. Love to fix bikes, golf, play pool, fish, bike ride, travel and build things. I have been married, to the same woman for 41yrs, have three boys, and three grandchil...
I decided to build my own air compressor. This project takes some time and skill as there is lots of welding and complicated fittings involved. I can not give you a specific list of the fittings you will require as your project my be configured differently from mine. So I will give you the basics and you can customize your own.


100 Pound propane tank (second tank optional)
Compressor motor
120/220 volt electric motor
Flat Iron 3"
10 " steel U-channel 32" long
Air switch
one way air valve
Tank water drain valve
Variety of brass and gas pipe fittings.
Pipe joint compound
Pressure gauge
Air Regulator


To start with and this is very important, a 100 pound propane tank that is completely drained of propane and should be aired out for at least several months as you will be welding to this tank. I sure don't want anyone blowed up.

Take your 3" flat iron, should be 1/4" thick and bend it at both ends at 90 degrees. You will need two of these. The length of the flat iron is up to you depending on the height you want your compressor. My pieces were 26" long and the middle piece is 12" with the 90 degree bends being 7" on each side. These are the legs. Weld these legs to the propane tank at the front and back making sure they are level with each other. With this done you can now place the tank on the floor and it should be solid.

Next take your piece of 10" steel U-channel and put the air compressor motor at the back of the tank and electric motor the front on this U-channel making sure that there will be enough tension on the drive belt. Mark the position of the mounting hole on both. Drill out these holes. Now put in the nuts and bolts you will be using to mount these two motors. Turn the U-channel upside down and weld the nuts to the under side. Once these are welded, remove the bolts. Place the U-channel on the top of the tank, opposite the legs. Make sure this is level and weld the U-channel to the tank. At the back of the tank you will have to drill out a hole big enough to fit the seat of the one way air valve. You know have to weld the valve seat to the tank making sure you have a complete seal on the weld.

Turn the tank upside down so the legs are up in the air. At the front of the tank on the bottom (where the legs are) drill and tap a hole that will fit the brass fitting you will use as a water drain. Once this is done and the fitting is installed with a on/off valve, turn the tank back over and mount your air compressor motor and electric motor. You need to run an air line from the air compressor motor to the one way air valve at the back of the tank. I re-wired my electric motor from 120 volt to 220 volt and put a 220 volt plug on it. There was too much initial electrical drain when the motor started up on 120 volts and would blow breakers.

You know have the basic compressor done. You know have to decide on the configuration you would like for your air outlet. You will need a reduction fitting to fit into the threaded hole where the original propane valve was. From there install the fittings you want . You will have to incorporate the air switch in your configuration. I used a Penn switch that is wired from the electric motor then out to the plug in. I adjusted the air switch to shut off at 110 pounds of pressure. Prior to the air switch you will also need a air pressure relief valve. For my compressor I also put in a T-fitting to run a line to a second 100 pound propane tank for extra air storage. I also put in an air regulator on mine. Be sure to use pipe joint compound on all the fittings to seal them. You should now be able to plug in the motor and fill the tank with air.


This is fairly complicated project and requires careful planning. These are fairly basic instructions, but should be good enough to get you started. The biggest concern is to not weld through the tank. Dry fit all of your fittings to make sure you have the configuration the way you want. Good luck and if you have any questions please email. Looking at the photos will give you a good reference. I know there is a lot of smarter guys out there and if you have any suggestions on how to improve or simplify this project, your comments are most welcome and will those of you who decide to take on this project.




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    25 Discussions

    Great project. Couple of suggestions...

    1. Draw a hard vacuum on the tank to evacuate any remaining propane. Ebay/Amazon have a plethora of affordable pumps for A/C and degassing tasks which are capable of pulling a full bar of vacuum, which should be enough to render your tank safe.

    2. Fille the tanks to the brim with water. This is the accepted method of purging any remaining propane before repurposing a tank.


    awesome project dude! does anyone know if i would have problems using an old propane tank for extra air capacity for shooting primer???


    awesome project dude! does anyone know if i would have problems using an old propane tank for extra air capacity for shooting primer???

    Well done for the project. I've been wanting to do such an air compressor for quite some time.

    Can I ask a question, any idea from what I can recycle an electric motor and compressor motor?

    I was also wondering whether an Air conditioner/Refrigerator compressor would work, since I believe this would be able to compress air into the tank without the need of a separate motor and compressor.

    Thanks a lot for your help!

    Hi Thanks for looking, mine does the same thing it slows down as it fills. I will work itself until it shuts off, but does strain. I think what I need is a stronger electric motor, but mine works good enough not to go to the extra expense. Not sure if this helps or not. Thanks again.

    Hi. I have a similar compressor, but it ran for about 10 mins and then started to strain and slowing down completely as if needing power for the motor. Any ideas plse

    You can also safely pressure test your tank by applying pressure while it is full of water, if it breaks out, it will not explode, just throw water... Use a long hose anyway !!!

    1 reply

    Good Morning and thanks for the comments and the instruction. This will certainly help those who wish to build one. Thanks for looking and helping.

    I've got an old propane tank that was built in 1963 and am considering Turing into an air compressor the tank only has surface rust and it was still holing propane when I got it. It says it's designed to handle 265 psi at 300 degreese F. But because it is so old I'm looking for advice on weather or not it's safe to reuse for air. What do u think would u use it?

    1 reply

    Hi and thanks for looking, I would have the tank pressure tested before I did anything. Thick wall tanks do last a long time, but if there is any moisture inside, it could rust and create a weak point. Safety first, if unsure, don't use the tank. Thanks again, and good luck.

    Amazing! I built the same machine several years ago. My neighbor gave me the tank and the triple stage compressor / 5hp motor was laying around. The compressor replentishes the tank faster than I can consume the air with pneumatic tools, even high volume air grinders. I would have to spend several hundred dollars to purchase an equal capacity compressor from the store.

    Safety is definately important when welding during construction and using high pressure air afterwards.

    I have a Sears compressor, but no tank attached to it. I have a separate tank. I have thought of putting them together, but the shut-off switch and some of the necessary fittings begin to get expensive. It would probably be cheaper for me to sell the compressor and tank I have now so I could simply go out and buy a home duty compressor with tank attached. Thank you for posting.

    8 replies

    Hi Phil, Thanks for looking and commenting. The spare tank was around and it was free. My son got the air hose and fittings and they were free, so for me it was easy. I do agree that some of the fittings are pricy, but I guess that is the price we pay for wanting to build stuff. Thanks again.

    Hi, I think your best bet would be to check out a scrap metal dealer or a propane business. Both should have old tanks. Remember to let the tank air out or fill it with water before welding. Thanks for looking.

    I would be safer to buy. a few people died at a rock yard here a few years back from an employee welding his own air compressor tank in the business shop. When he tested it out the tank blew taking out himself and some of his coworkers.

    You're right it would be safer to buy. I have had this compressor now for about 15 yrs and it still works great, but like I said in the instructable, you have to be very careful. My tank aired out for a couple of years. What I do like is the heavy construction of the propane tank to begin with. If you want to make your own, you might be better off to buy a brand new 100 lb tank and you don't have to worry about latent gases. Thanks for the comments and for viewing.

    I do think you did a nice job, and you did put a warning. The newer tanks do not seem to be as think as they used to be, I wish I could take a huge outside propane tank and build a compressor for it but I wont as I am not interested in the liability.

    See, that is why I have my buckets of scrap fittings. I never know when I want to make something like this (air manifold):