Degassing propane tanks (for Grant)

Hi Grant,

I spent a while yesterday looking at people's project pages and came across your propane tank degassing page. I've considered reusing propane tanks on several occasions, but had a different method of degassing in mind. Before I get to the details I should point out that our propane tanks (in the UK) might be a little different from yours, and that I'm talking about the largest (47 kg) variety.

I'm not thinking of trying this right now, so this post is just for your interest really. These tanks appeal to me because, having built a few high voltage machines, I want a source of large conductive metal spheres (or near spheres) to use as discharge terminals. The custom made aluminium spheres cost hundreds of pounds each, whereas as you've already pointed out, these tanks are often free. Our tanks have a convex top and bottom, and my idea was to remove two tank bases and stick weld them together to made a large conductive dome. The base ring and handle/valve protector could be removed from the cylinders easily. The resulting terminal would be damn near indestructible, unlike the usual spun aluminium spheres which are easily dented.

My plan was to take an "officially empty" cylinder out into our field (we have no neighbours nearby) on a cool day, make sure it was away from any sources of ignition and slowly open the valve to vent the propane to the atmosphere. When the propane inside was at atmospheric pressure, I intended to remove the valve and fill the tank with water from a hose to expel the remaining propane. Not having removed a tank valve, I'm not sure how easy it would be to fill the tank with water, but it seems like a neat way to remove all the remaining propane. What do you think? I'd be interested to hear your views.

Best wishes,


Reply to
Christopher Tidy
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The bleeding off of the gas I did slowly i.e. I didn't open the valve fully, I just cracked it and let it hiss slightly for several hours. When it stopped hissing then I brought it inside to warm it up (I did it on a cold day) and then repeated it. Then I opened the valve fully and turned it upside down and let it get as aired out as it would (I'm not sure this actually does anything). Then I pressurized the tank to about 140psi with compressed air and vented it again. I repeated the pressurize/vent cycle 3 times. By that time I figure what was left inside wouldn't burn, too diluted.

Then I clamped the tank, heated the neck to release the thread locker, and, using a big wrench, I unscrewed the valve. No point at all in trying to get water into one of those valves, gotta get it out fully. With the valve out, then I ran it mostly full of hot water and poured in a cup or so of household bleach, then plugged it and shook it all up (for a larger tank, I'd have rolled it around for a couple of minutes) then drained out the solution. No more stink.

It isn't easy to remove the valve without a way to rigidly clamp the tank. With the tank clamped, however, it's pretty easy as long as you use heat.


Reply to
Grant Erwin

If you google in RCM, you will find some experiments someone did trying to get more than a whoosh out of a propane tank when igniting a optimum gas air mixture.


Reply to

Take the valve(s) out and turn it over for a day. The gas will run out, it's considerably heavier than air. I've cut dozens of LP tanks, from

20lb to 1000gal. without problem, except for a couple that flashed because I didn't let them drain long enough.

When cutting sealed containers I always make a point to start as far from the hole as possible. If it does flash at least the fire isn't between the not-yet burned mixture and the hole.


Reply to

When I did this, I opened the fill vent, opened the main valve and then held a running hose against the main valve fitting until water came out the vent. jk

Reply to

Just thought...I could use me recently-acquired vacuum pump to de-gas the tanks and pipe the propane elsewhere.


Reply to
Christopher Tidy

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