Black iron cannon

DYI · Tue Jul 17, 2007 8:57 pm

Somebody with the means to do so really should pressure test galvanised steel, 150psi rated fittings and pipe to see what they can actually withstand, as that seems to be the only way to really solve this (although your burst pressure calcs on the pipe are probably accurate)
Anyone with a 4500psi scuba tank air compressor?

SpudBlaster15 · Tue Jul 17, 2007 11:35 pm

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noname · Wed Jul 18, 2007 10:49 am

Also, use your frickin' intellect! "Hmmm, I'm really worried about safety and I don't want it to blow up at 200 psi. PVC is rated to 280 psi and STEEL is only rated to 150. I'll take the PVC."

DYI, I've used them without any hassle in an 8x hybrid mix.

acoop101 · Wed Jul 18, 2007 12:00 pm

All I know for sure is that the cheap pipe fittings are rated for less than 200 psi. While the pipe can withstand 2000+ psi your system is only as strong as it's weakest link. All I am saying is to make sure to know what the working pressure is and make sure your system doesn't exceed it or you risk it going off like a hand grenade and spraying shrapnel all over the place.

acoop101 · Wed Jul 18, 2007 12:05 pm

I work as a T.I.G. welder, I work with high pressure systems regularly, I know there is a safety rating on parts, I know that it is on average about 1/10th of the failure pressure, but if you take that pressure above the working pressure it's at your own risk and the company can't be held responsible. But who really needs to build a cannon that uses more than 150 psi?

spanerman · Wed Jul 18, 2007 12:05 pm

yes, but any kind of steel(within reason) is better for holding pressure then pvc....duh...id take steel/maleable iron over pvc any day....iron can take ALOT of pressure...not 150psi...and ive never used malleable iron....but id bet its ok for alot more then 150psi, coke bottles take 150psi...

acoop101 · Wed Jul 18, 2007 12:09 pm

You can do what you want but I've seen steel pressure vessels fail and it's not nice.

I'm just asking people to check the ratings before they go exceeding them so they don't hurt them selves or others.

spanerman · Wed Jul 18, 2007 12:11 pm

yeah.. i bet its ugly...the pipe il be using in my hybrid is about a 5mm wall thinkness with a weld seam on it...only on the inside tho..

is that ok?

pvcmaster · Wed Jul 18, 2007 12:17 pm

Although my topic seems to have been taken over, i could still use some help. I went out and bought some silicone sealant, but i dont know if it is correct because it doesnt say anything about pressure use...

Also, how do I apply it, how much should i use, and should i wipe off any excess sealant? How long does it take to cure?

acoop101 · Wed Jul 18, 2007 12:44 pm

That should work fine but details of the project would give us a better idea of what would work, for my iron cannon, which I over built and can an do take up to 500 psi only uses Teflon tape to seal the gaps.

DYI · Wed Jul 18, 2007 1:00 pm

This choice between PVC and steel isn't really an option for me, since pressure rated PVC is practically non-existent where I live, I just don't think it's a great idea to take any material too far past it's rated working pressure. SB15 was a great advocate of non pressure rated solid wall ABS pipe before his advanced combustion exploded on him. Just because a material has been used several times above it's rated working pressure, doesn't mean that it is always safe to do so. Manufacturing defects do happen, and although it is probably safer to use 150psi rated iron at 300psi than it is to use 200psi rated PVC at the same pressure with compressed gas, I personally wouldn't try either one while I was anywhere near it.

noname · Wed Jul 18, 2007 1:51 pm

That looks like the right stuff. It doesn't say anything about pressure on mine either. I just put a 1/4" thick layer on the first two or three threads of the male fitting, then screw it in as far as possible. Then I wipe off the excess silicone that gets globbed on the fitting. The cure time is usually 24 hours, and if you take less than that, it will spring leaks and you'll have to do it over again.