Author Topic: Propane tank to air tank conversion  (Read 1716 times)

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Offline diogofcr

  • Posts: 5
Propane tank to air tank conversion
« on: January 01, 2017, 05:20 PM »
Hello, I got a new and empty big propane tank from a neighbour (he works at the propane distribution in the city) and I wanted to convert it to an air tank. I know even thought it looks like it, the tanks are never empty so my plan would be taking off the valve and filling it with water in order to remove any gas in the tank left. After that I was thinking about adding rust proof paint inside and rolling it around so it got in every place and let it dry for like a week or something, I read somewhere you shouldn't do this because it would contaminate the air line?! The last problem would be the drain valve, what should I do? I know I am not supposed to weld to the tank so that option is out, I was thinking about drilling and tapping a hole but I read somewhere that the tank is too thin to do that and the last option would be turning it upside down but the problem is that it would contaminate the air line with water. What should I do?

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Offline LooseSox

  • Posts: 35
Re: Propane tank to air tank conversion
« Reply #1 on: February 15, 2017, 01:23 AM »
Run a water trap between the tank and the line? Would remove the water issue.

Offline Corwin

  • Posts: 2380
Re: Propane tank to air tank conversion
« Reply #2 on: February 15, 2017, 04:17 AM »
... the tanks are never empty so my plan would be taking off the valve and filling it with water in order to remove any gas ... adding rust proof paint inside and rolling it around ...  the drain valve, what should I do? ... last option would be turning it upside down but the problem is that it would contaminate the air line with water. What should I do?

I don't know if emptying the tank further is needed. And, don't know what to think about rust proofing. But, I would mount it upside down and connect it to a vertical line that is terminated at the bottom with either a petcock bleeder valve or an air compressor separator to drain off the water. Input and output branches can be on an angle so they also drain into the vertical line.
Looks like your rabbit joint is a hare off! ;)

Offline them700project

  • Posts: 57
Re: Propane tank to air tank conversion
« Reply #3 on: February 15, 2017, 10:43 AM »
It can be welded to if you fill it with water first to disperse the propane i would say the best result would be to have a drain at the low point and pull and fill from the top or side.

Offline diogofcr

  • Posts: 5
Re: Propane tank to air tank conversion
« Reply #4 on: March 03, 2017, 04:06 PM »
Run a water trap between the tank and the line? Would remove the water issue.


I don't know if emptying the tank further is needed. And, don't know what to think about rust proofing. But, I would mount it upside down and connect it to a vertical line that is terminated at the bottom with either a petcock bleeder valve or an air compressor separator to drain off the water. Input and output branches can be on an angle so they also drain into the vertical line.


It can be welded to if you fill it with water first to disperse the propane i would say the best result would be to have a drain at the low point and pull and fill from the top or side.

Hello, first of all thank you for all of your replies, by the time you answered I already had done the project :P Here are some pictures and I will explain how I did it.
First I got a new (validation date is until 2031) empty propane tank and coated the inside with rust proof paint and waited really long for it to dry.
Basically it is like this image:

The propane tank is the "Vacuum bottle" The drain is like the rubber tube (but without the part that goes inside, it will be at the lowest point of the propane tank) and the "thermometer" is like the air line, (it has a tube that goes to like the middle of the propane tank, that way water won't get in the air line).

I made this piece on a lathe:




This other images will explain the setup better:








Explination:
The green disk represents the existing tank wall. The blue cylinder represents a threaded (?) plug inserted in the valve opening. The blue cylinder does not need to extend higher than the tank wall surface, but is exaggerated here. The red cylinder represents the air exit line and should extend above the tank wall, to prevent water "ingestion" when in use. The white cylinder should be as low as possible on the bottom of the blue cylinder, in order to eject as much water as possible. Of course, there would be valves on both exit cylinders to control air and water flow.


This is how the setup turned out:



Far away from the place where I work so if it decides to ever blow up (which I don't think it will) it won't hurt me.
This way I didnt have to do any welds and it works flawlessly. If you want to do this project I think you should, because it tripled the storage of my compressor and these can stand safely 30 bar (all of them in my country are tested to this pressure) and some of them are even tested to 100 bar. If you have any questions about this ask and I will answer