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Fire Extinguisher to brass fitting converter

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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Fire Extinguisher to brass fitting converter

Unread postAuthor: big_boom » Tue Jun 05, 2012 2:19 am

hi there,
so i plan on making an airsoft sniper rifle, i have it pretty much planned out except for one thing. i'm not sure how to connect the air chamber (a fire extinguisher) to the rest of the brass (BSP thread) fittings i will be using, if they are different that is. i tried searching on here but couldn't really find anything, or on google. i've seen people do it (one utube) so i know it can be done but u lack the knowledge.
another question, i'm going to buy the QEV and i have a choice of 1/8", 1/4" or 1/2". would a 1/8" or 1/4" allow enough air through for a 6mm barrel or should i go bigger?
any advice would be much appreciated, so thanks in advance.
Mick
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Unread postAuthor: jmez1996 » Tue Jun 05, 2012 3:09 am

I used a 1/4" QEV for both my airguns

http://www.spudfiles.com/forums/files/c ... on_178.jpg

the larger is 4.5mm barrel and the smaller is about 6.5mm barrel
and the valve allowed more than adequate air flow so i would use 1/4"

as for the fire extinguisher you might have to resort to epoxy. i epoxied a 1/2" brass bsp fitting into the opening of a fire extinguisher and it holds 250psi fine.
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Unread postAuthor: mattyzip77 » Tue Jun 05, 2012 6:45 am

Awww man!! I seen the title and thought I was gonna see a set! :evil:
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Unread postAuthor: Crna Legija » Tue Jun 05, 2012 7:04 am

You can weld a ftting in to the end.
Image
or epoxy it in.[/url]
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Unread postAuthor: big_boom » Tue Jun 05, 2012 7:20 am

jmez1996,
i will consider that method, but will hold out incase i find a tank that can be attached without glue/epoxy and solely relying on the fittings (or fix the fire extinguisher using brass fittings)
what other options for air chambers are there? any that already have some sort of standard thread (NPT/BSP) so at least i can buy a converter?
thanks again
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 05, 2012 7:52 am

Assuming you're staying below 250 psi, you might want to consider a used propane or MAPP tank.
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Unread postAuthor: mr.potatohead » Tue Jun 05, 2012 2:09 pm

i used an empty mapp gas tank and they work great and since the are kindof skinny the look very nice to
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Unread postAuthor: big_boom » Tue Jun 05, 2012 4:37 pm

yeah, by the sounds of it i might get a propane/mapp gas tank. they can be connected straight to the brass fittings?

What i have got is the tank off one of these-
http://www.google.com.au/imgres?q=propa ... 3,s:0,i:97
the top hole is small as well, not sure if it will allow enough air flow-
http://www.google.com.au/imgres?q=propa ... ,s:20,i:13
anyone know what pressure they are safe up to?
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Last edited by jrrdw on Thu Nov 28, 2013 2:23 pm, edited 1 time in total.
Reason: Double posting.

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Unread postAuthor: jackssmirkingrevenge » Tue Jun 05, 2012 11:36 pm

From your own link:

Construction is simple: get empty propane tank; make sure it's empty; unscrew and remove the two valves; wash out with soap and water; drill and tap for 1/4-inch NPT; clean; paint; replace the pressure-relief valve.


You can tap it for 1/4" BSP too, that will be more than enough flow and a tap is quite cheap.

As to the safe pressure, again from your own link:

How much pressure does propane generate? It depends on the temperature:

At a temperature of 70° F, propane's vapor pressure is 124 PSI.
At a temperature of 162° F, propane's vapor pressure is 390 PSI.

Propane tanks are equipped with pressure relief valves that vent excess pressure. If the tank gets too hot, the tank will fart instead of explode. :-)

Normal propane cylinders, such as those used with portable grills have pressure relief valves set to 375 PSI. PRV settings for ASME (American Society of Mechanical Engineers) tanks are 250 PSI. DOT engine fuel cylinders use PRV settings of 312.5 PSI.

During manufacture of propane cylinders for engine fuel storage, each propane cylinder must be exposed to two times its service pressure, and one out of every 500 cylinders is exposed to four times its pressure, or about 960 PSI.

It would seem that propane tanks are built to withstand at least 250 PSI. I think it logical to assume that any propane cylinder you are likely to encounter can withstand at least 200 PSI virtually indefinitely.

So, what kind of load will we be putting on them? Regulations for home and shop air compressors limit them to 125 PSI.

I think propane tanks can safely handle the pressure that a home compressor can dish out.
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Unread postAuthor: big_boom » Wed Jun 06, 2012 1:30 am

wow, didn't mean to waste your time when the info was right under my nose... thanks anyway :)

actually, just checked a 3/4" fitting on one of the propane tanks linked above and it fits good. haven't tested it under pressure yet but for those looking for the info...
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Last edited by jrrdw on Thu Nov 28, 2013 2:19 pm, edited 1 time in total.
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Re: Fire Extinguisher to brass fitting converter

Unread postAuthor: T_Money » Thu Nov 28, 2013 8:41 am

guys i found an excellent solution. SodaStream Co2tanks. They say they are rated for something crazy like 350bar, but I just go around 30 bar. You need to remove the label and wrap the bottle (you can get 130L or 60L tanks-just go to staples or somewhere, amazon has them, look on sodastream website) in duct tape or something equal to prevent damage. then you will see a hex screw sticking out of the side-very small. Unscrew it ccw very slowly, let it drain in an open space where you wont suffocate (not in your closet). Once hissing stops, unscrew that completely. When that is out, any last bits of co2 drains out. Then clamp the tape covered bottle in a vise (I put some wood in my vise for further protection). Get a wrench that fits the slot on the big brass valve. It's on very tight, so it may be challenging. Turn ccw. Once loose, it will be very easy. On the shaft, there is an o-ring followed by about 65mm of ridiculously fine threads. Unscrew. Move the bottle to somewhere you won't lose it like I managed to do. If the vise method didn't work for you, wrap bottle in a ton of tape and on that tape use a large pipe wrench, put it on tight and then use a wrench for the brass valve's notch. This can be done by a 15 year old me, and very easily with 2 people. Then put the valve in your mill or drill press or if you aren't really spoiled, a vise and a hand drill. then take a 11.11ish mm (7/16") drill bit and drill out the center of the valve. there is a pin that is spring loaded, so keep pressing down with your drill until you start taking out the brass around that hole. Drill all the way through. it may be easier to go in from the bottom. Both the pin and an internal disk will break loose and spin freely which require lots of force to break through and it makes tons of heat (friction can be reduced with lots of lube). Once your through, get some pliers or something and clean out that hole completely. then tap it with a 1/4" npt tap and lots of lube and forearm strength (nothing intended there). Then I chose to put the small screw that releases the pressure back and TIG weld it into place/seal off holes. You could just lug hole with something and use high pressure epoxy. If you tig weld use 140amps on dc, same brass as the base material-I actually brazed it with silicon bronze on 70 amps (foot pedal) wear a respirator (zinc). Then I put an air fitting in and put it in as far as it would go down and proceeded to bed it in a ton of 100 bar epoxy. I hope that this helps. It took me about an hour in total. Sorry for the five page essay on a simple task. Any questions pm me. I am not responsible for any of the stupid stuff you do and end up with a body full of stainless.
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