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Old 03-28-2010, 12:35 PM #1
Boom Master
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Join Date: May 2009
Location: St. Louis MO, USA, EARTH
Fire Extinguisher Air Chamber - HOW TO

OK, let's do this right. I used a 2 pound, ABC Kiddie Brand, disposible-one time use, non-rechargable, kitchen/boat fire extinguisher body.

I get them for FREE or $2 at my local fire extinguisher supplier. They salvage the dry chemical if it went flat and lost pressure and sell the aluminum body for scrap. Found two dead ones at garage sales for a quarter each. So are CHEAP and plentiful. Go to LOWES and buy a brand new one for $25.

According to a Tech, Aluminum Fire extinguisher bodies splits under pressure and generates little or NO schrapnel. They decided to shoot a couple of outdated but pressurized ones with a rifle just to see what happened. (He may have left out the 'drinking at the time' part.) Bullet holes with a split. So I doubt an application in paintball would be much more abusive than that.

The fire extinguisher body weighs considerable LESS than an equal volume air chamber made out of PVC Pipe which DOES turn into schrapnel when they fail under pressure.

Below was a staged failure to illustrate WHY you may not want to use PVC for an air chamber. 150 psi shot with a .22 rifle.

So it is CHEAPER, SAFER, LIGHTER to use these readily available fire extinguisher bodies than "old school" PVC pipe to make air chambers for Nerf cannons and bazookas.

Below is the pic of cutting off the stock nozzle. It is a reinforced PLASTIC fitting. You have to disassemble the valve and remove all the metal parts first and then I screwed the empty nozzle back onto the body to hold it true and square when I cut it off with a table saw.

Below is drilling the hole for the tap. That spade bit I ground down to the profile I needed for the tap. I didn't have the drill bit and if I did, didn't have a drill press big enough to hold it. So I fudged.

Here's a pic of the ground spade bit.

Below is tapping the 1/2" NPT into the drilled Nozzle Fitting of the Fire Extinguisher. Put the tap upside down in a vice and used the fire extinguisher body for a handle. Worked. More fudge factor.

Below is the 1/2" NPT nipple with NO untreaded shoulder on the LEFT. You can see the nipple on the RIGHT is too long for the final fitting to seat onto the neck of the fire extinguisher but you COULD just screw it into your valve fitting.

Below is a reducer fitting 1/2" NPT to 1" NPT to screw directly into my 1" valve fitting.

In the Shorty picture below, the 1/2" nipple is screwed directly into that 1/2 NPT 4 way / Cross fitting and seated on the shoulder of the fire extinguiser body for extra mechanical strength.

I just wanted it mechanically REAL BEEFY for the abuse on the field it has gotten. It has been banged around for 4 seasons without a hitch.

I used a pipe extractor tool to screw that shoulderless pipe nipple into place with some BLUE Loctite on it. Then put the reducer fitting on with Blue Loctite on it and screwed it down TIGHT onto the neck shoulder of the body. Let them BOTH set up over night before assembling it further.

Below is an illustrated pic of the Shorty.

You must have a pressure guage and a pressure relief valve. The one seen is 150 psi.

Paintball regulators DO fail.

The one on my Shorty saved my bacon ONCE. I was using a dual regulated paintball air tank (4500 psi) with the second stage output at 145 psi. It was trying to match the air tanks internal pressure at 4500 psi but very slowly. The pressure relief valve would fart about every 4-5 minutes. Figured it was just the hot day and the reg output maybe just a tad high. Went to check it and noted the pressure guage creeping up slowly. Then I remembered that I blew a remote hose using that tank with a marker. Used my spare and it blew too. NOW I knew why..... A Bad reg on that air tank. Without it on my Shorty, a 300+ psi explosion would have happened in the staging area with a bunch of people around without masks on.

NOW I turn off my air supply and discharge any pressure before entering the staging area... Double safe. Just in case........
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Old 03-28-2010, 07:44 PM #2
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Hmmmmmm I have an old fire extinguisher laying around in my house that's empty....... This gives me a good idea of what to do with it now Thanks Boom Master!
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Old 03-31-2010, 12:46 PM #3
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very nice, out my office window i can see a pile of used fire extinguishers at the safety place across the street.

can you post a pic of your whole rig and a closeup on the loader area also?
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Old 03-31-2010, 03:59 PM #4
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Nice post. you got any ideas for a larger valve than a sprinkler? My current configuration on my "Project" is using a 1 inch orbit valve attatched to a 4 inch by 24 inch air chamber.which holds a very good amount of volume. but its not enough for what im trying to do. a sup air valve would be too big for my aplication. ive seen pneumatic valves that are somwehat compact. any ideas on were to get one for an air cannon application
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Old 03-31-2010, 09:06 PM #5
Boom Master
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Location: St. Louis MO, USA, EARTH
I don't feel you need a Larger valve to shoot nerfs. So curious what your application is..

They make them, cost more, weigh more, but why go there when your $12-20 sprinkler valve will get a Nerf up to 230 fps out of a 24-28" long barrel? I tried TWO 1" sprinkler valves in parrallel with a disappointing but slight increase in velocity with the same operating pressure, barrel length, etc.

If you want to go there, here is a source for you:

Here is a 1 1/2" sprinkler

And a 2"

Pretty much a monster valve.

Now the measurement is the pipe size that screws into it. NOT the internal size of the diaphragm orifice which is what we need to know about flow rates.. For example in checking the replacement part numbers for the diaphragms, I discovered the diaphragm for the 3/4" and 1" is an identical part number.

That 1 1/2" and 2" might be the SAME internally as well. Check the part number to see if the replacement parts for the diaphragm is the same. If not, then one is likely larger.

By the way, their tech support is very helpful with specs and such until you mention "paintball cannon".

I think the reason is that sprinklers are not designed to open particularly fast. Nor close very fast either. Just fast enough to work for our cannons.

Why should they? Just turning on/off the water to sprinkle some grass.. Diaphragm valves have to vent the space above the diaphragm to open the valve. They use a relatively SMALL port to vent it through. 0.060" or so that is opened by the solenoid valve.

It takes TIME to vent all that cavity to allow the diaphragm to move up into it.

In fact, according to Dave Halls Gas Gun Design Tool, the Nerf is LONG GONE out the barrel before the diaphragm gets to open COMPLETELY in barrels under 36". By comparison, that all metal quick exhaust has a 1/2" internal orifice but performs the SAME as a diaphragm valve with a 3/4" internal orifice because that shop air valve can vent a LOT of air out of it much more quickly than through a .060" vent.

The bigger the valve, the bigger the cavity above the diaphragm and may or may not be venting through a larger vent port run by the solenoid. So it could potentially open even SLOWER if they use that same .060" port and the same solenoid valve to trigger it.

That $35 QE-5 Quick Exhaust Valve shown in the pic is the biggest one I could find that didn't cost a fortune or weigh a ton. Search "Quick Exhaust" pneumatic and valves and have your credit card handy.

The Shorty. Link with info at:

I have a whole set of pictures how to make that sliding breech loader. It uses several "Slip" or "Slide" Union PVC fittings. They have no taper or ridge in the middle like typical pvc union fittings.

E mail me for them or wait until I can get them up to post.
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