In Line/ Portable Air Tank Out of a Propane Tank




This is a old air tank that I use for starting fires and for filling my air cannon.

This tank was made with parts that where on hand a many many years ago. I had to take it apart because of a small leak and wanted to show how it was made.

Use an EMPTY propane tank. You don't want gas leaking out and causing an explosion. Also compressed air can be dangerous. I'm not sure what a propane tank is rated for but keeping the PSI at a reasonable amount should be OK.

Step 1: Whats Needed

Parts (All in sizes inches)

  • standard EMPTY BBQ propane tank with vale removed. Preferably newer then the one I used
  • Air gauge 0-100 PSI (could go higher then 100)
  • 1/4 female T
  • 1/4 T male/female though female take off
  • 1/4 male nipple
  • 3/4 to 1/2 reducer
  • 1/2 to 1/4 reducer
  • 2 female air couplings
  • pipe joint compound

  • 5/8 wrench
  • 11/16 wrecnh
  • 3/4 wrench
  • 3/8 to 1-1/4 adjustable wrench (1" wrench)

If needed, a regular pipe wrench .

Step 2: Removing the Propane Tank Valve.

I am not so sure on this part. Find a wrench that fits and apply some torque.

Step 3: 3/4 to 1/2 Reducer

Apply joint compound around threads and screw it in. The reducer needs to be very tight so it does not come lose.

Step 4: 1/2 to 1/4 Reducer

Apply joint compound around threads and screw it in. A 3/4 wrench should tighten it.

Step 5: 1/4 Male/femal Through Female Take Off

Apply joint compound around bottom thread and screw it in. Tighten the T with a 3/4 wrench to where it points at where the gap is in the rim/handle on the tank.

Step 6: Gauge

Apply joint compound around threads and screw in the air gauge. Tighten with wrench to where the the text is readable and not lopsided. I used a 0-100 PSI but higher is OK. The compressor I use only puts out 115 PSI.

Step 7: 1/4 Male Nipple

Apply joint compound around one of the threads and screw it in. Tighten with wrench.

Step 8: 1/4 Female T

Apply joint compound around threads of the nipple and tighten the with a wrench to the T is in line with the other T.

Step 9: Air Couplings

This can be done 2 ways I prefer using one coupling.

2 couplings
Apply joint compound around threads of each one and screw and tighten them into both sides of the T
Use step 10 to fill the tank.

1 coupling
or just one on the side by the gauge and use step 11 to fill the tank.

Step 10: How to Fill It OP.1

Not so safe way. This was my original way of filling the tank.

  • 2 1/4 male couplings
  • 1/4 male ball valve.

Step 11: How to Fill It OP.2

The safer way. Also easier to fill the tank.

  • 1/4 male coupling
  • 1/4 male ball valve

This also makes the tank a bit more portable and with the ball valve handle inside the rim. Chances the valve will open are slim.

Step 12: Test for Leaks and Fill Up.

Test for leaks by connecting the male coupling to the air line and turn the ball valve to open.

Look for any bubbling of the joint compound at the connections.

If there are not leaks then it is good to use.

Keeping the tank inline should help keep the pressure longer before the compressor cycles. Close the valve and release the coupling and you have a portable tank for airing tires, starting fires, and filling air cannons.

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    16 Discussions


    5 years ago

    can you take a 1lb propane tank and swap it to air?


    5 years ago on Introduction

    Is it not a 'idea' to use a household cylinder for a year, and then cycle that back into the supply from the gas men? If you have gas heating, then you'll go through a fair few cylinders, so why not us one that is already checked, and of a known suitability, then after a year or two swap it out for a 'new' one?


    6 years ago on Step 12

    This is just what i've been looking for. Instead of buying a bigger comp with larger tank this seems to be the answer, great idea.

    1 reply
    Rob Kvincentmcmurray

    Reply 6 years ago on Step 12

    I have seen these at a few job sites. doing it this way they can make a few for the cost of one of those 5 gallon inline air tanks. Ours is in need of repair. The ball valve is seized up and can only be run inline and not able to hold air when disconnected. A quick fix but I have not done it yet.


    8 years ago on Introduction

    household bleach will remove the mercaptan from the tanks. as far as disposal i used household haz-mat disposal in my community

    I've been thinking about extending the capacity of my air compressor by adding three 20# propane tanks I have kicking around from a time prior to the valve design change. Given that the compressor cannot produce any more than 125 # of pressure, the tanks should be fine.

    My idea is to add them inline using 3/4" Schedule M copper pipe. I'm not interested in quick removal; these are intended to stay in place.  I plan to  mount them upside down off the main copper line so they become self draining. If I set up the line in my garage / workshop horizontally along one of the roof trusses, the pipe can support the tanks in line. I'm planning to use 3/4" threaded adapters to tees inline and add a dropped water trap similar to a raised air hammer chamber in home plumbing, but with a ball valve at the end to pull off the accumulated water. Tees along the line can provide access for tools and so forth. Any thoughts?


    9 years ago on Introduction

    Propane tanks are DOT certified, and must be re-tested every 5 years. The hydro is to not only verify the pressure rating, but a "real" hydrostatic test measures the tanks ability to return to an established % or it's original size after a 1.25 to 1.5 x over the maximum opperating presure rating. The "pop off" valve needs to be sized for not only a specific pressure rating, but also a discharge capacity rating. The discharge capacity is calculated by the maximum floww rate of the filling device, or the maximum pressure temperature (gas expansion) due to exposue to fire. I have no idea what corrosion allowances are designed into the tanks, but I'll bet wet compressed air is not as health for them as dry propane. Would I do this? Probably, but it would make me a little nervous!


    9 years ago on Step 12

    Very creative, simplistic and functional. Nice job and nice instructable, thanks. I have some constructive safety comments: 1) You can hydro-test the tank by filling with water and then pressurizing with the highest pressure compressor you will potentially fill the tank up with. If it fails the it will only leak (spray) water and not potentially fail catastrphically as it could if it failed with only air in it. 2) Once you have established that the tank will work with this pressure you can substitute the first "T" connector with a "X" or cross and then screw in a pressure relieving valve which is calibrated to blow (pop off) at a pressure 10 PSI (or more) below the successful hydro-tested pressure. This will ensure that you do not exceed your tested pressure and will allow for some degradation to occur and still remain safe. 3) Make it a point to regularly drain the tank to reduce corrosion. Corrosion will happen and will reduce the pressure holding capability for any steel tank. 4) Mind Exercise: When thinking of pressure and how a tank can fail , think of of PSI over a square foot. 1 PSI over 1 square foot = 144 lbs force. the same square foot with 100 PSI acting on it = 14,400 lbs force. 125 PSI =18,000 lbs force. That's a lot of force! Now where are those old propane tanks at...

    1 reply
    Rob KBaytonian

    Reply 9 years ago on Step 12

    Thanks for the info on hydro testing. I was not sure on how that was done. The tank really needs to be replaced. Over 15 years of use or more of not using a moisture filter the tank was full of a rusty dust.

    Rob K

    9 years ago on Introduction

    Thought that was just added to the propane gas. As for this tank it has been used for an air tank for the last 15 years or so.

    Rob KStrangeRanger

    Reply 10 years ago on Introduction

    You would maybe need to remove the valve first. Or find away to force water into the open valve.


    10 years ago on Introduction

    With a propane tank, 250 psi SHOULD be a safe pressure(asme standard pressure reliefe setting). I THINK standard 50# grill tanks have their blowbys set to 375#. Either way, I would highly recommend staying under 200#. Also, use a new(but recently emptied) tank. An older, banged up starting to rust tank like shown, will tend to fail much more frequently than a new tank, and at those pressures failure may be "exciting".

    1 reply
    Rob Kironsmiter

    Reply 10 years ago on Introduction

    This tank has about seen its days 15+ years. I will probably get another year or two out of it before it gets replaced. Thanks for the info on pressure. This was the standard grill 20 pound tank. I think that is what its called.


    10 years ago on Introduction

    A couple precautions for all of those that are fool hardy. Open valve and vent off for a couple of days. Avoid sparks, use non-sparking tools to remove valve. touch a grounded piece of metal before attempting to remove valve avoiding a static spark. Ground propane tank before de-valving and fill with water like MacMan45 recommends.


    To be sure the tank is empty of propane, you can fill it with water, which will push out any residual gas. (then just dump out the water and let it dry) Especially useful if you plan to cut the tank or weld anything to it!!