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Fire extinguisher as high pressure tank?

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j.azz

Tue Sept 30 2008, 02:35PM

Registered Member #888 Joined: Tue Jul 10 2007, 06:52PM
Location: Hannover, Germany
Posts: 40

Hi folks!

I've got an (older) portable CO2 fire extinguisher that I want to use as a high pressure air tank.
It's burst plate is rated at 250Bar (kg/cm^2), the tank itself is tested up to 950Bar. As I found on the internet, the operating pressure is about 70Bar at room temperature.

Now my question is:
Up to which pressure can I use it? Will the original valve held as much as the tank?
Can I go above the rating of the burst plate if I remove it?

thx in advance, j.azz

Dr. Slack

Tue Sept 30 2008, 03:10PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

If you remove the burst plate, then the tank will only be able to go up to 0 bar.

However if you replace the burst plate with something stronger, then you'll have a system suitable for the iterative capacity measurement method, which runs roughly thus - Increase pressure (voltage, current, power input, borrowings against bad mortgages) until it goes bang (bursts into flames, economy collapses), then back off a bit.

As a tip, test it hydarulically, rather than pneumatically. A failure at 950bar with water will result in a fright. A 950 bar failure with air will take out most of the neighbourhood.

j.azz

Tue Sept 30 2008, 03:31PM

Registered Member #888 Joined: Tue Jul 10 2007, 06:52PM
Location: Hannover, Germany
Posts: 40

Ok. With saying removing the burst plate I thought of replacing it ;)
As I heard these fire ext. tanks are coated internally against corrosion from the CO2, so the iron won't be harmed by water either, right?
Guess I'll try that as soon as I get a suitable pressure supply.
But as I only have this one, I'll need another one that works after the test,
is there someone in Germany who sells me an old CO2 fire ext. up to 2litres CO2?

thx, j.azz

Steve Conner

Tue Sept 30 2008, 04:18PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

It all depends on how much risk you want to take, bearing in mind that the energy released in an explosion would be similar to a couple of hand grenades.

If it was to be used near people without any shielding, then the 250 bar rating of the burst disc is what counts. (Even 250 bar is a heck of a lot of pressure.)

For short-term experimental use, you might be able to go up to, say, half the test pressure of the tank, but you wouldn't want to hang out near it for long.

Exploding one tank would probably not be a reliable source of data. There are variations in manufacture, and things happen to them after they leave the factory.

Of course this post is provided without any warranty and I disclaim all responsibility for any damage or injury you might suffer, which is likely to be gruesome

ragnar

Tue Sept 30 2008, 04:27PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

I'm quite sure they have some kind of pressure relief valve anyway?

aonomus

Tue Sept 30 2008, 08:00PM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

I think they do hydrostatic testing on fire extinguisher tanks. They submerge the tank into water, and fill the tank with water and increase the pressure until the test rating. Any failure will result in little/no shrapnel iirc...

Sync

Tue Sept 30 2008, 08:02PM

Registered Member #510 Joined: Sat Feb 10 2007, 09:28AM
Location: Hannover
Posts: 12

Thats what the burstplate ist for... And yes they are coated with some paint inside..

Und ich geh schonmal in Deckung wenn du das Teil ansteckst...

rp181

Tue Sept 30 2008, 11:52PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

whats it for?

Dragon64

Wed Oct 01 2008, 12:02AM

Registered Member #1438 Joined: Sat Apr 12 2008, 12:57AM
Location: Canada
Posts: 218

Matt Bingham wrote ...

I'm quite sure they have some kind of pressure relief valve anyway?

He is right, there is a automatic pressure release valve in fire extinguisher as a safty feature.

Mythbuster tried to burst a fire extinguisher in a camp fire but never did because the safty valve opened releasing all the gas.

Dr. Slack

Wed Oct 01 2008, 07:08AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

But as I only have this one, I'll need another one that works after the test,

Unfortunately, failing one tank only tells you about that one tank, so you can't assume anything about any others. That's why there's a difference between the test pressure (which tells you that the tank stood that pressure once, before it was knocked about or suffered corrosion), the burst disk pressure, and the operating pressure.

If you're a mnaufacturer, and you make a whole bunch of tanks from the same batch of material, then you can start quoting pressures for ones you haven't tested to destruction.

If you test one to destruction, and buy a "similar" one and expect it to behave the same way, at the extreme end of its range where it's not designed to work ...

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