Using an out of service fire extinguisher as an air tank
Using an out of service fire extinguisher as an air tank
(OP)
I'm trying to discourage someone doing such as a "bad idea" and would like to hear your thoughts.
1. Typical red 3 gallon fire extinguisher is one that has been taken out of service due to time limits
2. Top nozzle has been replaced by a welding in a coupling
3. Mounting tabs welded onto shell
4. Operating the fire extinguisher at 100 psi and using it as an on board air system on an off-road vehicle
Thanks.
1. Typical red 3 gallon fire extinguisher is one that has been taken out of service due to time limits
2. Top nozzle has been replaced by a welding in a coupling
3. Mounting tabs welded onto shell
4. Operating the fire extinguisher at 100 psi and using it as an on board air system on an off-road vehicle
Thanks.
Brian





RE: Using an out of service fire extinguisher as an air tank
RE: Using an out of service fire extinguisher as an air tank
RE: Using an out of service fire extinguisher as an air tank
This is NOT me using this, but someone well-respected on an off-roading public forum, so it is in essence encouraging others to be extremely foolish.
Most folks have never heard of the "code" or have a clue about such things, yet I've already pointed out the code issue(s), the fact that it is being used in a way it was not intended to be used, and the modifications by welding...falling on deaf ears.
Thus I'm looking for a more convincing argument other than it is a "bad idea". They just aren't "getting it" and what is worse, others are chiming in saying they don't see anything wrong with it cause they've never had a "problem" with it.
Thanks.
Brian
RE: Using an out of service fire extinguisher as an air tank
"Art without engineering is dreaming; Engineering without art is calculating."
Steven K. Roberts, Technomad
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
RE: Using an out of service fire extinguisher as an air tank
It seems to me that you covered the essentials in your second post. You provided the necessary warning. If people still choose to follow someone else’s idea or recommendation, there is nothing more you can say or do. Don't waste your time with this...
RE: Using an out of service fire extinguisher as an air tank
RE: Using an out of service fire extinguisher as an air tank
Welding on any pressure containing device is stupid. The original properties are a function of alloy composition, mechaical forming and heat treatment.
Would these same people buy high quality after-market suspention springs and then weld on them? Would they weld on rotating engine componants?
You could also suggest that they hydro test a unit to see what pressure it will hold. A saftey factor of less than 4:1 would be risky. I have done home-made-hydro. It isn't too hard.
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Rust never sleeps
Neither should your protection
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RE: Using an out of service fire extinguisher as an air tank
Are the "tabs" designed to not be stress raisers & not cause high local stresses?
The National Board has a nice write up on "air receivers":
ht
look under par. #3 "problems"
RE: Using an out of service fire extinguisher as an air tank
Thanks for the link.
Brian
RE: Using an out of service fire extinguisher as an air tank
Sometimes God must thin the herd..... Darwin developed a theory on this very concept
God often uses boilers and pressure vessels in mysterious ways.....
Warn others.....
-MJC
RE: Using an out of service fire extinguisher as an air tank
Auto parts stores in a certain very large state once sold kits to convert propane tanks (used for gas grills) to compressed air receivers. That state did not have a pressure vessel law. In one Summer, two people lost arms to bursting "converted" propane tanks. The auto parts stores that sold the kits were found to be liable for the financial consequences. That state now has a pressure vessel law.
The problem is that most people are not pressure technology engineers and there are blissfully ignorant of the hazards implicit in operating such equipment. If the kit is sold, or if it shows you how on the internet........
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.............then it MUST be OK, right? Hey, this is great stuff, you can run your paintball gun from these tanks all season - or until you only have one arm left! See, it seem like there is always somebody who want to ruin your fun.
RE: Using an out of service fire extinguisher as an air tank
Brian
RE: Using an out of service fire extinguisher as an air tank
While it must be appreciated that you have brought your concerns out into the open technical forum, I guess the "someone well-respected" must also be alerted immediately to the potential hazards of his improvization.
Every knowledgeable person must take the initiative to bring together the user and the area inspector or other authorized person when there is a potential hazard.
I am sure you will actually be doing a favor to your friend, who incidentally is only ignorant of certain issues and not necessarily stupid, (see "Using an old, clean, undamaged fire ext. as an air tank is not the most stupid thing that you could do."-EdStainless, above).
RE: Using an out of service fire extinguisher as an air tank
Next class on used fire equipment will cover those who ask for a used fire \ extinguisher because they are only going to have a small fire, and those who want a used fire sprinkler head to mount over the wood stove.
RE: Using an out of service fire extinguisher as an air tank
I promptly took my conversion tank (what can I say, I was young when I made it) stripped it, drilled some holes in it and set it out by the curb. I am now somewhat leery about even filling tires.
It's better to be lucky than good.
Mike
RE: Using an out of service fire extinguisher as an air tank
Brian
RE: Using an out of service fire extinguisher as an air tank
In the ensuing years we gave some employees the direction and materials to check their individual shop and farm compressors. A good percentage reported back that they found cracks when they checked their tanks.
The worst ones were the larger service station size 2 stage compressors. I have seen 3 catastrophic failures of the vertical 2 stage type and 1 of the large horizontal type. I've seen two of the 3-5 gal home style with long seam ruptures and numerous ones cracking and leaking.
RE: Using an out of service fire extinguisher as an air tank
Mike
RE: Using an out of service fire extinguisher as an air tank
Brian
RE: Using an out of service fire extinguisher as an air tank
Well, that's just the thing I guess, there's nothing wrong with having a air compressor in your garage. People do it all the time. All kinds of old ones everywhere. Who knows how they get maintained? It's for sure they never get inspected. I've heard people talk about making air tanks from old water heaters. It's a wonder that kind of thing doesn't happen more often.
One trend that bothers me is that as engineering tools have gotten "better", particularily for consumer products, every bit of margin is being taken out of everything to be able sell at the lowest possible price. A little extra steel can be cheap insurance.
Mike
RE: Using an out of service fire extinguisher as an air tank
Well, this thread is realy wandering away from the original topic but I will add this:
Unclesyd is absolutely correct. It was a little known fact that "tank mounted compressors" (TMC's) were having pressure vessel failures all over the country about 25 tears ago. NASA was just getting into their "pressure vessel and pressure system recertification program" at their research centers and they were warned by an engineering consultant who had recently completed strain gage testing (and testing to destruction) of various manufacturer's TMC's. Reciprocating compressors provide a great amount of vibration sitting on top of the air receiver. The testing found that the (rather small and intermittant) fillet welds that attached the compressor platform to the air receiver were the most frequent site of crack initiation that eventually propagated through the vessel's wall and "bang". NASA had all their TMC's modified to dismount the compressor from the air receiver. The next frequent location for (vibration) fatigue induced cracks was at the location on the bottom of the air receivers where the mounting "feet" were attached by fillet welds to the "tank's" bottom - if these were bolted to a concrete floor, it took fewer cycles for the failure to occur. A trade organization had a guide developed to help the TMC manufacturers "design out" the problem. However, now you can find many TMC's on sale that are imported and have not benefited by the design guide. I guess it is just a matter of time before they are in the news again.
RE: Using an out of service fire extinguisher as an air tank
@JohnBreen:
The design guide you mentioned needs to be given wide publicity and the necessary awareness created in the professional circles.
RE: Using an out of service fire extinguisher as an air tank
But the trade organization (which is funded by the subscriptions of the equipment manufacturers) paid the consultant to do the testing and to write the guide. The guide is consequently the intellectual property of the trade organization. Have you ever seen the prices (gasp) that EPRI wants for their reports?
When in doubt, dismount the compressor (take it off the platform that is welded to the top wall of the air receiver) and mount it separately. Alternately, examine the platform-to-vessel welds and the feet-to-vessel welds by PT or MT regularly.
RE: Using an out of service fire extinguisher as an air tank
Luckily nobody died, but they have scars to show-off.
If the idiot wants a tank, let him by a descent airtank designed for it. There are a lot of trucks with air compressor, air brakes winches and other air operated stuff, which work close to 125 psi.
Have you ever have seen the classic video of what happens when a cylinder falls and the valve breaks off? It turns into a rocket.
RE: Using an out of service fire extinguisher as an air tank
@waskillywabbit:
I suppose you must show one such video to your friends. That should help.
RE: Using an out of service fire extinguisher as an air tank
If the off-roader had used the original threaded connection and clamped rather than welded the "vessel" to his vehicle, his risk would be greatly minimized. As Ed says, using a fire extinguisher designed for 275 psig to contain air at ~ 100 psig isn't the stupidest thing people do on a daily basis. Personally, I'd feel safer with a good quality fire extinguisher shell in my garage than I would with one of the flimsy non-branded Chinese hobbyist pancake compressors! The brand-name people are making them in China too, but they're worried about product liability a little more than the non-branded Chinese factories are, for sure, and it shows in the construction of the tanks.
Good comments about the weld attachments for mounting compressors- definitely an accident waiting to happen if done improperly, and also widely (and poorly) done. Especially on those cheap non-branded units!
I think we'll be seeing a lot of these hobbyist units blowing up in about ten to twenty years. Typical scenario would be an explosion when somebody re-starts one of these units to fill a tire after the tank has been sitting in their garage for ten years, undrained and silently rotting from the inside out...