Compressed air bottle for small pneumatic purposes

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Sir Cumference
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Compressed air bottle for small pneumatic purposes

Post by Sir Cumference »

Some time ago the use of soda-bottles as pressure vessels were discussed at the forum.

The problem is, that they are not rated for the pressure delivered by a compressor. 8 bars are just about the burst pressure..... and what a bang when they do!

A powder extinguisher is a nice way to solve the problem.
It is designed for being at 15 bars for years on end, and it is tested to 30 bars.


Start with a spent extinguisher (or two :mrgreen: )
extinguisher 001 (Small).jpg

Step one: Make sure it really is depressurized!

Unscrew the small pressure gauge. Should any pressure remain, it will come out that way, rather than shooting the handle into your face!

- Unscrew the hose

- Drill out the rivets holding the handle and remove the handle.

- Unscrew the handle/valve-assembly with attached riser tube.
Some powder will remain! Pour it carefully out in a bag, and discard it in your household waste.
The 6kg bottle had a handfull remaining, but in the 2kg bottle almost 1kg powder was left (they were both well past the "use by"-date)
The powder is an irritant to inhale, quite corrosive on most metals when wet, and a killer of electronics!
Fill the bottle with warm water and a couple of drops of detergent to dissolve any remaining powder.
extinguisher 002 (Small).jpg
- take the valve assembly apart, and clean the parts in warm soapy water.
There are typically two ways of pressurizing the extinguishers:
Either through the nozzle
or
Through a Schrader-valve on the valve assembly

I had one of each:
Nozzle type:
extinguisher 004 (Small).jpg
and Schrader type:
extinguisher 005 (Small).jpg

Check that the bottle is clean and dry, oil the inside of it, replace any worn O-ring or give the original a bit of silicone grease and assemble everything again.

Reinstall the handle/trigger again, replacing the rivets with a couple of bolts.

A compressed air coupler will fit in the original nossle thread, and the bottle can be pressurized, just like you would pump a tire if it is the Schrader type.
If it is the nozzle type, an unmodified bottle must be filled trough the nozzle.
extinguisher 007 (Small).jpg
Remove the sticker to make sure you do not mistake your air bottle for an extinguisher the day something is on fire!
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Sir Cumference
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Re: Compressed air bottle for small pneumatic purposes

Post by Sir Cumference »

extinguisher 006 (Small).jpg
Finished bottles with stickers removed.

Variations
When the bottles are used like this, the handle must be depressed to let out air.
In some cases that is great:
"Pull a pin to release a weight that presses the lever and the pneumatic cylinder on the stocks is activated"
... or you can just tape the handle down to keep it open.


The nossle type can be modified with a Schrader valve if you want to.
Cut the rubber of an auto-mobile valve, remove the valve parts from the extinguisher and soft solder the valve into the hole where the valve stem was previously.


In a "6 kg bottle" there is enough air for a surprising lot of air cylinder operations.
(And more than enough to pump your bicycle)


WARNING:
Do not drill, grind or weld on the bottles.
If you do that you may compromise the strength...... and exploding pressure vessels are real killers!
Use only bottles in good condition. No dents, deep scratches or deep corrosion!
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Re: Compressed air bottle for small pneumatic purposes

Post by ponylady »

Sir Cumference wrote:WARNING:
Do not drill, grind or weld on the bottles.
If you do that you may compromise the strength...... and exploding pressure vessels are real killers!
Use only bottles in good condition. No dents, deep scratches or deep corrosion!
nice idea, but you could just rent a gas bottle from your local propane/butane gas-supplier and "abuse" them
with air. advantage is they already come equipped with a regulated valve, no tinkering needed.
of course, if you have countless old FE lying around you might have a new businessidea for the selfbondagcrowd.
[
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Re: Compressed air bottle for small pneumatic purposes

Post by Needleplayer »

Good idea! Have used 2 pieces, 6 Kg fire extinguishers to tank for my vacuum pump for quick suction. It is unlikely to rust inside the tank but check it anyway at the bottom.

As mentioned at previous NEVER MAKE CHANGES IN TANK AND CHANGE THE TRIGGER MECHANISM TO DO WITH CARE. I have seen the result of the pressure vessel explode and it's not a nice sight.

Agree with "ponylady" to use propane / butane tank. The steels are rarely used now and especially 5kg tank. Paint the tank a different color, so one can see the difference in the original and new uses.
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Re: Compressed air bottle for small pneumatic purposes

Post by Sir Cumference »

just use a propane tank
Have you ever done that?

At least in my part of the world, an odorant is added to alert you in case of leaks.
The normal one is ethane thiol, one of the most smelly compounds known to man. And the tank keeps stinking.

I have used propane tanks, and air from them smells just like a gas leak.
I know a guy who had a home-made compressor made from an 11kg LPG-bottle. Even after ten years of use, it still stunk!
(memory and smells are connected. Whenever I smell LPG, my first thought is not "gas", but that awful home-made compressor)
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Re: Compressed air bottle for small pneumatic purposes

Post by iceman »

Get a Co2 system. Most home improvement stores sell them, comes with a Co2 bottle and an air regulator to reduce the pressure to the level that you get from a standard air compressor. I use them to power air nailers when I can't easily run hoses to the location. They use the same C02 bottles that paint ball guns use, so they can be refilled where you can get paint ball supplies or the home improvement stores that sell them also either refill or exchange empty bottles.
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Re: Compressed air bottle for small pneumatic purposes

Post by Sir Cumference »

Yes, in some respects a CO2-system will be very nice.

In my part of the world (again, it is a big world, and I can't see where you are from?), I have however never seen the system you describe for hobby use.
Furthermore, the legislation regarding compressed gases other than LPG is quite harsh here, requiring frequent pressure tests and resulting in high prices.

A CO2 system is great because it will deliver a lot of gas at a constant pressure. Running a pneumatic cylinder in a back-and-forth for an extended time could need it.
(It should be noted, that letting too much CO2 out in a small room could be dangerous. A valve malfunction could be lethal)


Having a limited amount of compressed air is preferable in some cases.
You could make a back-up time release using a needle valve or other "controlled leak", and an emergency release could be as simple as a glass tube you break or a ball valve to kick open.
Doing that with CO2 would be a very lengthy process in the first case and possibly dangerous in the other.

For the occasional swat (think cylinder, electropneumatic valve and a riding crop) or keeping a cylinder in a position, there is more than enough air in a 6kg bottle.

Around here compressed air pressure regulators are reasonably cheap, pressure regulators for compressed gases are in a price range 10 times higher.




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Re: Compressed air bottle for small pneumatic purposes

Post by iceman »

In the US, CNG tanks are more closely monitored here than are the CO2 bottles used for paintball guns. I have a CO2 bottle that is over 20 years old and no one has ever mentioned anything when I have had it refilled. On the other hand I've had to replace all four of my CNG tanks more than once over that time period for various reasons.

Here's one of the more common kits that I have used in the past.
http://www.lowes.com/pd_166441-61735-J- ... facetInfo=
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Re: Compressed air bottle for small pneumatic purposes

Post by slkdyk »

Don't forget those air carry tanks from the auto parts store.

http://homerepair.about.com/od/toolsmat ... irtank.htm
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Re: Compressed air bottle for small pneumatic purposes

Post by Riddle »

Sir Cumference,

Nice write-up on using fire extinguishers for storing air. What pressure is required to put the guage into the green?
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Re: Compressed air bottle for small pneumatic purposes

Post by bound_jenny »

Riddle wrote:Sir Cumference,

Nice write-up on using fire extinguishers for storing air. What pressure is required to put the gauge into the green?
This should answer your question:
Sir Cumference wrote:It is designed for being at 15 bars for years on end, and it is tested to 30 bars.
The gauge, in closer inspection, goes from 0 to 20. Assuming that is also in bars, the green area starts at 10. 1 bar = 1 atmosphere, or about 15 psi (willingly rounded off, so don't anyone stickle me), so about 150 psi is the figure if you're not a metric person.

Of course, this figure will be different depending on the fire extinguisher. Some will take more, some less. Read the label and the gauge.

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Sir Cumference
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Re: Compressed air bottle for small pneumatic purposes

Post by Sir Cumference »

slkdyk wrote:Don't forget those air carry tanks from the auto parts store.

http://homerepair.about.com/od/toolsmat ... irtank.htm
Cute!
If you live in an area where those are available, there is little need to take the DIY approach.


For 30$ you can hardly buy the parts!
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Re: Compressed air bottle for small pneumatic purposes

Post by Dark_Lizerd »

I watched Mythbusters...
They covered the "bomb" that is in everyone's house...
The hot water tank....
The 55 gal. one made hell of a blast!!!

I bet air tanks can do just as much damage...
At best, it would ring your ears, at worse, well.....
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Re: Compressed air bottle for small pneumatic purposes

Post by bound_jenny »

The hot water tank... also a good source of power (as the Mythbusters also demonstrated).

How about a naughty Victorian-like steam-powered apparatus with all sorts of polished brass levers and valves and other superb workmanship operated, of course, by some classic villain in a cape, top hat and handlebar mustache... :mrgreen:

That's probably the result if Gord went steampunk... :rofl:

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Re: Compressed air bottle for small pneumatic purposes

Post by Riddle »

bound_jenny wrote: How about a naughty Victorian-like steam-powered apparatus with all sorts of polished brass levers and valves and other superb workmanship... :mrgreen:

That's probably the result if Gord went steampunk... :rofl:

Jenny.
:rofl:

Would be nice to have my DIY resemble Victorian craftsmanship... At least my mustache is well kept.

Dark_Lizerd wrote: I bet air tanks can do just as much damage...
At best, it would ring your ears, at worse, well.....
The potential damage is certainly greater; compressed gas makes a water-filled pressure vessel rupture appear benign in comparison.
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