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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: Ragnarok » Tue Jul 08, 2008 4:57 am

D_Hall wrote:Are these real problems? I have no idea. They're just two possibilities that pop into my mind.

Of course, these days, there are plastics which have relatively low melting points - Polycaprolactone has a melting point of around 60 degrees C.

Whether or not these materials are practical in other ways is a matter I'm far from knowledgeable enough to talk about, but a material with a melting point that low does get around the second problem you mentioned, and helps with the first pretty well.
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Unread postAuthor: DYI » Tue Jul 08, 2008 8:01 pm

A 6" ID chamber with an OD of 30"...

Even with a relatively low grade steel, that's a static yield pressure of around 150k psi, and I don't think LGGs are made of very low grade steel. With a higher grade steel, we're talking over 400k psi.

I've never really heard an accurate figure of the chamber pressure generated by these things, but I'm guessing it's high enough that there's not a tremendous safety factor on the pump tube.
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Unread postAuthor: D_Hall » Wed Jul 09, 2008 1:35 am

DYI wrote:I've never really heard an accurate figure of the chamber pressure generated by these things, but I'm guessing it's high enough that there's not a tremendous safety factor on the pump tube.

We were operating in the 120-140 ksi region.
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Unread postAuthor: sandman » Wed Jul 09, 2008 4:37 pm

um, i know this is kinda random, but if you would fill the chamber with some water would that cushion the piston so that it wouldn't be destroyed?
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Unread postAuthor: DYI » Wed Jul 09, 2008 10:12 pm

um, i know this is kinda random, but if you would fill the chamber with some water would that cushion the piston so that it wouldn't be destroyed?


1. Water is incompressible, so liquid water can't really absorb any shock at all.

2. That made absolutely no sense...
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Unread postAuthor: psycix » Thu Jul 10, 2008 5:43 am

sandman wrote:um, i know this is kinda random, but if you would fill the chamber with some water would that cushion the piston so that it wouldn't be destroyed?

Why dont you try it? :lol:
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Unread postAuthor: D_Hall » Thu Jul 10, 2008 12:32 pm

And it's that shock at the end that generates the insane pressures. Let the piston gracefully stop and those pressures go away. Ergo, you've defeated the purpose of having the gun to begin with.
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Unread postAuthor: sandman » Thu Jul 10, 2008 10:12 pm

kk, i didnt think it was that easy, just wondering
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