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first piston

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: colty-bear » Thu Jul 16, 2009 2:46 pm

i just finished my first piston today a copper/brass fittings coaxial
it works beautifully at 150psi but that is not enough pressure for me
if it is copper pipe and copper and brass fittings what psi will it hold?
i am thinking about getting a 400 psi pump
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Unread postAuthor: Hotwired » Thu Jul 16, 2009 3:06 pm

The weakest copper pipe I know of is metric plumbing pipe.

That is safe to over 300psi all the way to 54mm diameter and smaller sizes such as 15mm, 22mm and 28mm are fine with 600psi.

Imperial pipe seems to be thicker than the metric versions so it may well have higher pressure ratings.

The pressures above refer to the actual working pressure not bursting pressure.
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Unread postAuthor: colty-bear » Thu Jul 16, 2009 3:14 pm

it is straight cut copper it is 5/8 and the barrel is 1/4 the reducer is copper but the trigger assembly is brass
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Unread postAuthor: far_cry » Thu Jul 16, 2009 3:41 pm

400 psi its ok

if you can you give some spec and pictures this will help better
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Unread postAuthor: colty-bear » Thu Jul 16, 2009 3:57 pm

i will when i fix it :( i just finished it today and after about 20 shots it was leaking real bad so i unscrewed it and the inner barrel stamped a hole in the rubber sealing face! it was slightly sharp though so i took a file and hit the pipe to blunt it up a little
should that keep it from cutting the rubber?
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Unread postAuthor: jrrdw » Thu Jul 16, 2009 4:37 pm

Is your piston hammering shut? if so it's gonna keep cutting it. Try harder rubber.
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Unread postAuthor: colty-bear » Thu Jul 16, 2009 4:45 pm

it only moves about 3/4 inch but it was also slightly sharp from being cut so i made it blunt ill try again if that dosn't work ill find harder rubber
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Unread postAuthor: far_cry » Thu Jul 16, 2009 5:27 pm

harder rubber also will be cut
you must make a bigger edge

or find something fits on the barrel edge and glow it
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Unread postAuthor: colty-bear » Thu Jul 16, 2009 5:34 pm

that is going to be VERY hard the chamber is 5/8 and the barrel is 1/4 the barrel is about 2 inches in from where i can unscrew the trigger assembly
if i cut an old car tire would that not cut?
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Unread postAuthor: far_cry » Thu Jul 16, 2009 7:20 pm

try the car tire . much better than what did you used for the first time
make sure the rubber is flat and 5 mm thick
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Unread postAuthor: colty-bear » Fri Jul 17, 2009 12:47 am

fixed! i got it fixed for now. I think :shock:
is it bad if you can hear a slight leak probably losing 1psi every second? will that change when i put higher pressure in it?
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Unread postAuthor: jackssmirkingrevenge » Fri Jul 17, 2009 12:53 am

colty-bear wrote:the inner barrel stamped a hole in the rubber sealing face!


Happened to me when I started plaing with higher pressures. Harder rubber won't really help in the long term, what I do is take a suitable sized length of tubing of larger diameter (for example pen tubes work well for 6mm barrels) and epoxy a short length to the breech end of the barrel to give a bigger surface area for the piston to rest on.
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Unread postAuthor: colty-bear » Fri Jul 17, 2009 1:20 am

the rubber i am using now is tractor tire rubber VERY HARD and seals up it wont stamp because it has wire running inside it to reinforce it.
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Unread postAuthor: jackssmirkingrevenge » Fri Jul 17, 2009 1:38 am

Won't it "stamp" until it reaches the wire, at which point it will stop sealing? Especially if you intend to up your pressures by almost 300%...
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Unread postAuthor: colty-bear » Fri Jul 17, 2009 2:50 am

well when i hit it, it made the end of the pipe flat

like so

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also the rubber is very tough i took a big sample and tried stabbing it a few times, like i said very tough outer rubber
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