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Piston valve

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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Unread postAuthor: ALIHISGREAT » Sun Oct 26, 2008 1:59 pm

Floyd wrote:For a pneumatic if cost doesn't matter, copper. If cost does matter, PVC.

Overall I would recommend PVC because if you use all pressure rated pipe and fittings it will withstand higher than most bike pumps can pump to.
But if you have a high pressure source go for copper.


copper is infinitley safer than PVC....
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Unread postAuthor: Gippeto » Sun Oct 26, 2008 11:38 pm

You need to think about how you are going to join the dissimilar metals.

You cannot solder, braze, or weld aluminum to copper or iron/steel.

Welding aluminum to aluminum requires special skills and tools.

Epoxy can work very well if done properly.

I find copper to be easy to work with and an excellent choice for a building material. Solder is my preferred method of joining it.

Don't bother brazing copper. The temperatures required to braze copper actually anneal the metal, and lower the pressure rating of the tube. Stick with solder and flux.

To put it plainly, the tube will rupture long before a properly soldered joint fails(calculated failure pressure), even with 50/50 lead/antimony solder.

There are several excellent copper piston guns in the pneumatic showcase section. Have a look, and see what you like.

If you decide to work with copper, download the copper tube handbook and give it a read.

http://www.copper.org/publications/pub_ ... ndbook.pdf
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Unread postAuthor: MrCrowley » Sun Oct 26, 2008 11:57 pm

You need to think about how you are going to join the dissimilar metals.

You cannot solder, braze, or weld aluminum to copper or iron/steel.

Welding aluminum to aluminum requires special skills and tools.

Epoxy can work very well if done properly

I think it'd be easier just to use threaded fittings :)
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Unread postAuthor: Gippeto » Mon Oct 27, 2008 12:03 am

Quite true, and a good point. :)
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Unread postAuthor: john bunsenburner » Mon Oct 27, 2008 1:18 am

so should i tap all my pipes or is that too much work? I just like alli barrels becuase they are thicker than the copper ones and also seem straiter(thats my hardware store). I cant really get any threded pipes here.
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Unread postAuthor: MrCrowley » Mon Oct 27, 2008 1:34 am

You can epoxy a brass/copper threaded adapter to the alli barrel and for the copper chamber and piston housing you can solder copper threaded adapters to the copper pipe.
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Unread postAuthor: POLAND_SPUD » Mon Oct 27, 2008 1:37 am

IMO the best thing you can do is to use malleable threaded fittings and pipes for the chamber and stuff.. by doing so you can:

1. play with your design - if you don't like it you can complettely rearrange it in several minutes
2. lower costs - becasue you can use all the parts you bought for your future projects

ohhh and use a copper/aluminium pipe for a barrel and join it to the rest of the gun via a compression fitting...
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