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Fire extinguisher and JB weld MAX psi?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Fire extinguisher and JB weld MAX psi?

Unread postAuthor: auxiliary » Wed Jul 23, 2008 7:02 pm

I am replacing the 2" PVC tank on my pneumatic rifle with hopefully a fire extinguisher tank. It is not a CO2 fire extinguisher, it is just a KIDDE powder filled tank that has a bit of air in it (class ABC extinguisher). The threads on it are definetly not NPT, but I decided to attach it to a 3/4in. galvanized nipple using JB weld. There was 2-3mm of space around the nipple and the threading of the tank so I applied steel wire around the nipple between the threads and that made the nipple snug and straight. I sanded down the wires and nipple and the threads of the tank and outside of the tank mouth before applying JB weld. I put on enough to where the outside the the tank mouth and 1in. of the smooth part of the nipple were covered in ~4mm of JB weld.

Will this stand up to pressures of 200-300psi?
Here's a picture of it:
http://www.putfile.com/pic/8481874
Here's a link to the fire extinguisher I used:
http://www.jr.com/kidde/pe/KDE_466142/
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Unread postAuthor: blind909 » Wed Jul 23, 2008 8:09 pm

Yes, It will hold. And JBweld will hold up to at least 500 psi, and is it J-B KWIK, or the original, J-B WELD?
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Unread postAuthor: auxiliary » Wed Jul 23, 2008 8:18 pm

That's comforting! And it is original JB weld. Does anybody know if the fire extinguisher tank will hold up?
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Unread postAuthor: Mr.Sandman » Wed Jul 23, 2008 8:26 pm

yea i think you should be safe up to 400 psi but i dont think you should take it up any higher than that. also are you by any chance using pvc or a sprinkler valve on your rifle cause it would be a very bad idea to take it up to 200-300 psi. at that pressure the valve would burst or fail and be a not so comforting thing to happen( actually, try massive amounts of shrapnel). but really what is the gun made of?
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Unread postAuthor: iisthemuffin » Wed Jul 23, 2008 8:43 pm

Mr.Sandman, the valve would not "burst". The diaphragm inside would simply rip. There is no way it could explode unless you securely blocked the end of the barrel and MADE the valve hold a couple of hundred psi.
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Unread postAuthor: Mr.Sandman » Wed Jul 23, 2008 8:50 pm

sorry i meant the pvc might rupture :oops: even so there is a possibility that the sprinkler valve might crack and rupture.
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Unread postAuthor: iisthemuffin » Wed Jul 23, 2008 8:53 pm

That would be so hard to happen though. You have to understand that the diaphragm is what holds the air inside of the valve and without that diaphragm, the air would just flow out the end of the valve. The diaphragm will rupture long before the valve even has a chance to crack.
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Unread postAuthor: Mr.Sandman » Wed Jul 23, 2008 9:06 pm

i know that but anything can happen.
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Unread postAuthor: iisthemuffin » Wed Jul 23, 2008 9:16 pm

No offense, but in my opinion, you realize your wonrg and now are trying to make something about your claim right. I dont meant hat in a mean way at all.

And it would be very hard for that to happen. Like i said, something would have to block the exhaust for the valve to even build up enough pressure.
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Unread postAuthor: Mr.Sandman » Wed Jul 23, 2008 9:18 pm

wow people over the internet are extremely smart :D :o :shock: 8) :lol: :x :oops:
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Unread postAuthor: auxiliary » Wed Jul 23, 2008 10:05 pm

I am using a brass 1/2in. spring loaded ball valve with a crude, but satisfactory trigger system so psi is no object to me. I still don't know if pumping up the fire extinguisher tank to 200-300psi would be safe though.
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Unread postAuthor: iisthemuffin » Wed Jul 23, 2008 11:05 pm

Mr.Sandman wrote:wow people over the internet are extremely smart :D :o :shock: 8) :lol: :x :oops:


I cant tell if your being sarcastic or if your amazed that i was right?


auxiliary wrote:I am using a brass 1/2in. spring loaded ball valve with a crude, but satisfactory trigger system so psi is no object to me. I still don't know if pumping up the fire extinguisher tank to 200-300psi would be safe though.


If the tank can hold that pressure you will be fine. I would wait for someone who has made a cannon with an extginuisher and ask them. I would say its ok, since it is made to hold a good amount of pressure.

If the epoxy job is done right, it seems you have done a fair job, then it should hold 300 EASYILY.
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Unread postAuthor: MrCrowley » Wed Jul 23, 2008 11:13 pm

I got mine welded but JB-Weld should do the job.

I believe those tanks are rated to 300psi with a bursting pressure probably around 3x that.

It looks like you did a good job with the JB-Weld but one bump could fracture the whole weld and render it useless. Always happens with me, JB-Weld cracks pretty easily.
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Unread postAuthor: dudeman508 » Wed Jul 23, 2008 11:19 pm

Did you weld it yourself
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Unread postAuthor: iisthemuffin » Wed Jul 23, 2008 11:21 pm

Huh. I use stuff called loctite weld. It dries very hard but its still kind of "soft" i would say. It feels very glossy. I dont see it cracking.

I guess its just the different brands.
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