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Metal pipes rusting

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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Metal pipes rusting

Unread postAuthor: potatoflinger » Sat Aug 04, 2007 2:38 pm

For a while now, I have been using metal pipe for cannons (Galvanized and black iron). Is it possible for the chamber to rust enough to be a hazard? With compressed air, moisture from the air goes in the chamber, but does the moisture leave the chamber when the gun is fired, or does the moisture stay and accumulate in the chamber? Any advice would be very much appreciated.
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Unread postAuthor: Kaiser Bill » Sat Aug 04, 2007 3:41 pm

from my experience working with pneumatic systems that have not being drained regularly the condensate will do little or no damage in the short term (sub 5 years)

but if you want to be safe you could feed the air through a dryer or inject a small amount of light oil in the chamber
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Unread postAuthor: BigJon » Sat Aug 04, 2007 4:43 pm

you could coat the inside with paint to keep it from rusting.
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Unread postAuthor: Marco321 » Sat Aug 04, 2007 7:04 pm

The galvanized iron will not rust. I'm not sure what black iron is, if it a sealant for the metal, it might rust were there is no paint, or if the paint gets scratched or stressed.

you could coat the inside with paint to keep it from rusting.
That will work as well for the inside, but again it will rust if it gets cracked or stressed due to differential aeration.

EDIT: My view is that it should be fine, just always check for rust, but if it is painted, you probably wont see the rust because it will be in a place were there is the least amount of oxygen. The best advice i could give is to not stress or crack the paint if it has some

I just looked up black iron, apparently is rusts in a different way which similar to aluminum. It creates a protective layer of rust, preventing any more rust from occurring, its like an alternative to galvanizing the metal.

So if you used galvanized metal and black iron you should be fine, moisture and air will not affect the pipes because they are chemically and physically protected from rust.
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Unread postAuthor: pyrogeek » Sat Aug 04, 2007 7:15 pm

I would think that the water would condense and leave a little behind even after firing. Painting the inside seems like a good way to screw up you valve, unless you painted it all befors assembling. Just squirting a little air tool oil into the air inlet would probably be the best idea. I don't think the gun will rust out very soon, but it would also help keep the valve's surfaces sealing well.
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Unread postAuthor: potatoflinger » Sat Aug 04, 2007 7:59 pm

Thanks for the replies, it seems like the cannons will last around five years, so I guess I'll be okay. I have a small filter on my compressor that takes a little bit of the moisture out of the air, but not all of it. I might consider getting one of those small silica gel air dryers for my compressor.
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Unread postAuthor: Modderxtrordanare » Sat Aug 04, 2007 8:04 pm

potatoflinger wrote:Thanks for the replies, it seems like the cannons will last around five years, so I guess I'll be okay. I have a small filter on my compressor that takes a little bit of the moisture out of the air, but not all of it. I might consider getting one of those small silica gel air dryers for my compressor.


You're supposed to open the little valve at the bottom of your compressor, then it won't rust inside from the water build up if you drain it all off. You don't need some silica gel dryer.
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Unread postAuthor: potatoflinger » Sat Aug 04, 2007 8:08 pm

Modderxtrordanare wrote:
potatoflinger wrote:Thanks for the replies, it seems like the cannons will last around five years, so I guess I'll be okay. I have a small filter on my compressor that takes a little bit of the moisture out of the air, but not all of it. I might consider getting one of those small silica gel air dryers for my compressor.


You're supposed to open the little valve at the bottom of your compressor, then it won't rust inside from the water build up if you drain it all off. You don't need some silica gel dryer.

I'm not talking about the compressor, I drain that every time I use it, I am talking about my pneumatic cannons. The dryer would dry the air that comes out of the compressor, and would then go into the cannon as dry air.
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Unread postAuthor: frankrede » Sun Aug 05, 2007 12:19 am

What pressure are you using?
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Unread postAuthor: potatoflinger » Sun Aug 05, 2007 9:53 am

frankrede wrote:What pressure are you using?

Around 100 to 150 psi, nothing outside the pipes pressure rating.
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Unread postAuthor: frankrede » Sun Aug 05, 2007 3:45 pm

well then I doubt rust would affect in at all.
Maybe if you were using unregulated co2 you might worry but at that pressure it should be fine.
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Unread postAuthor: jimmy101 » Sun Aug 05, 2007 4:34 pm

The air coming out of your compressor should be very dry, much drier than the air in the room. Compressing the air to ~120 PSI will remove most of the moisture (that is why you have to drain the tank periodically).

If you can leave the valve open when storing the gun that'll help dry out the inside of the chamber.

You could also drop a packet of silica gel in the barrel then stuff a rag in the muzzle to keep atmospheric moisture out of the gun.

If you are really paranoid, you can flush the gun with a dry gas before storing. Nitrogen, CO2, propane, butane, pretty much any compressed gas from a cylinder will be very dry. I wouldn't use an oxygen cylinder for obvious reasons.
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Unread postAuthor: potatoflinger » Sun Aug 05, 2007 7:11 pm

I was just curious, and it seems like there's nothing to worry about, thanks for all your help.
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