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Black iron cannon

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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Black iron cannon

Unread postAuthor: pvcmaster » Tue Jul 10, 2007 11:08 am

Im looking to build a black iron cannon next, but i have some questions and there is very little answers in the forums. First of all, is there a difference between black iron and malleable black iron, and would either be acceptable? Also the pipe and fittings just screw together, right, so all i would need is some teflon tape? This cannon will have a 3/4" QEV from McMaster as a valve, and i am planning to attach a 1/4" tee off the pilot area with a blowgun on one side, and a mini ball valve with a schrader on the other. Will this work for me? Thank you for anyone's help!
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Unread postAuthor: noname » Tue Jul 10, 2007 11:21 am

Both types of pipe will work, and your setup should work also. Yes, you need teflon tape, but I'd advise getting 3 or 4 rolls of it. I use about 8 inches of it for each 1/4" joint, and a bunch more for others. Do I get leaks in anything? No way.

Also, a good way to wrap the tape:
Hold the fitting so that the male threads are pointing to the left. Get a length of teflon tape, put the end of the strip on the threads, and then wrap it in the downwards direction.
This is the only way I can ever wrap teflon tape correctly; if you wrap it the wrong way (clockwise), it will get taken off when you screw the fitting in and will leak.

Edit: Another sure fire way of keeping threads sealed is globbing silicone sealant all over them, then screwing them together. I use sealant on all joints over 1" because they waste too much teflon tape. The silicone sealant holds upwards over 350 psi, but with a vice and some elbow grease you can get them apart later.
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Last edited by noname on Tue Jul 10, 2007 11:33 am, edited 1 time in total.
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Unread postAuthor: potatoflinger » Tue Jul 10, 2007 11:25 am

I don't know the difference between black iron and malleable black iron, but I have made two cannons out of black iron (not sure which type, but it said it was rated to 150 psi), and they work beautifully. And yes, if the pipe is threaded, the only thing you will need is teflon tape.
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Unread postAuthor: pvcmaster » Tue Jul 10, 2007 11:34 am

OK, thanks for both of your help.
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Unread postAuthor: Flying_Salt » Tue Jul 10, 2007 11:42 am

Here is a small black iron qev cannon. It pretty much answers your questions...
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Unread postAuthor: pvcmaster » Tue Jul 10, 2007 11:47 am

Yes, i did look at that cannon, but i fail to see the ball valve underneath the quick connect.

anyway, i noticed some people mentioning that these types of cannons are used in the winter. Is there something wrong with pvc in the cold weather?
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Unread postAuthor: noname » Tue Jul 10, 2007 11:53 am

PVC gets even more brittle in cold weather, thus raising the chance of pipe failure.
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Unread postAuthor: acoop101 » Thu Jul 12, 2007 6:51 pm

cast iron pipe fittings are only rated up to 125 psi, while I am sure that there is a large difference between the max working load and the destruction pressure I would never ever want to go over the working load.
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Unread postAuthor: acoop101 » Thu Jul 12, 2007 7:00 pm

if you are going to order form McMaster check out the presure ratings, they do have them on all of there black pipe fittings. The foraged steel fittings are rated up to 3000 p.s.i. but they do cost about three times as much.
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Unread postAuthor: pvcmaster » Tue Jul 17, 2007 7:33 pm

I am assembling the cannon now, and I am having some trouble tightening the endcap and elbow onto the main chamber nipple. Underwater they leak like crazy, and i dont have anything to grab on to to tighten them. Anyone have any suggestions?
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Unread postAuthor: frankrede » Tue Jul 17, 2007 7:55 pm

Try using teflon paste, it is about a dollar and it comes ina white tube, always seals my leaky threads.
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Unread postAuthor: SpudBlaster15 » Tue Jul 17, 2007 8:13 pm

acoop101 wrote:cast iron pipe fittings are only rated up to 125 psi, while I am sure that there is a large difference between the max working load and the destruction pressure I would never ever want to go over the working load.


I have calculated the burst pressure of a 1.5" Sch 40 pipe made of the cheapest steel possible, and it is well over 2000psi. So there is no reason to stay within the rated working pressure.
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Unread postAuthor: potatoflinger » Tue Jul 17, 2007 8:30 pm

pvcmaster wrote:I am assembling the cannon now, and I am having some trouble tightening the endcap and elbow onto the main chamber nipple. Underwater they leak like crazy, and i dont have anything to grab on to to tighten them. Anyone have any suggestions?

Try using an adjustable wrench like this one:
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Unread postAuthor: DYI » Tue Jul 17, 2007 8:36 pm

Or you could just use a proper pipe wrench.
SB15: But have you calculated the bursting pressure of the fittings? I am almost sure that they would fail long before the pipe would, unless they actually are the 3000 or 6000 PSI rated fittings from McMaster.
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Unread postAuthor: SpudBlaster15 » Tue Jul 17, 2007 8:48 pm

There is no reason to suggest that they would burst at a lower pressure, assuming they are made of similar material (which they are).
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