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Piston design critique....

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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Piston design critique....

Unread postAuthor: sco77 » Thu Sep 01, 2011 5:12 pm

I made this piston for my 1/8" coaxial gun with 12(10)" of 1/2" chamber, 1/8" 30" rod for barrel.

I didn't take a picture of the finished product but after this was taken the head of the bolt was dipped in epoxy resin for barrel sealing surface (about 1/10" thick, if that), the rubber part is bumper and pilot sealing surface (which was extended so no stud is exposed) and I added an extra o-ring... total piston travel: 1/4"~

10 minute pressure test @ 1000psi and 5 1000psi test shots, gun made for 400-500PSI.
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Unread postAuthor: mattyzip77 » Thu Sep 01, 2011 7:08 pm

looks good, me likey!!!!

300 posts! 8) 8) 8)
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Unread postAuthor: Gun Freak » Thu Sep 01, 2011 7:28 pm

Looks really heavy for a 1/2" piston.
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Unread postAuthor: sco77 » Fri Sep 02, 2011 12:49 am

Gun Freak wrote:Looks really heavy for a 1/2" piston.

It's not as heavy as it looks, but even so it's for high pressure, has a good seal and not a very big travel... It performs pretty nice and has a nice bang to it for being such a low caliber barrel.
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Unread postAuthor: Technician1002 » Fri Sep 02, 2011 1:02 am

It does not have to move far to open. The barrel is 1/8th inch. Valve is open at less than 1/16th inch travel.
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Unread postAuthor: jackssmirkingrevenge » Fri Sep 02, 2011 1:12 am

Looks a little over-engineered, for this 1/8" coaxial I got on fine at 850 psi with simply a rubber cylinder cut from 1/4" neoprene sheet.

Image
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Unread postAuthor: Brian the brain » Fri Sep 02, 2011 2:49 pm

:D

Can't get much better than this!
Love the simplicity.

I almost forgot I used a solid rubber disc on " the pirate" (pretty long ago!!) wich had a 15mm barrel port and I had no problem with it at 26 bar.
So 1/8" should work fine..
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: sco77 » Sat Sep 03, 2011 12:10 am

Does the valve sound like it's performing like it should? This is around 400psi about 10 feet from the camera..

[youtube]http://www.youtube.com/watch?v=57wtU3_YmHU&hd=1[/youtube]
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Unread postAuthor: jackssmirkingrevenge » Sat Sep 03, 2011 12:29 am

Sadly noise, especially recorded noise, is a poor indicator of shot power. What projectile are you shooting? A 1/8" ball bearing should go through both sides of a soup tin easily at 400 psi.
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Unread postAuthor: sco77 » Sat Sep 03, 2011 12:40 am

jackssmirkingrevenge wrote:Sadly noise, especially recorded noise, is a poor indicator of shot power. What projectile are you shooting? A 1/8" ball bearing should go through both sides of a soup tin easily at 400 psi.

That shot was just an indoor shot with rice (turns to powder after 1 layer of cardboard)..

I shot small screws and metal caps at 500PSI and went through some pretty thick metal (about 2x thickness of canned goods), and smashed or bent projectile. Unfortunately I have no way of measuring FPS so I don't know if it's performing as quickly as it should.
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Unread postAuthor: jackssmirkingrevenge » Sat Sep 03, 2011 12:42 am

sco77 wrote:I shot small screws and metal caps at 500PSI and went through some pretty thick metal (about 2x thickness of canned goods), and smashed or bent projectile. Unfortunately I have no way of measuring FPS so I don't know if it's performing as quickly as it should.


That sounds about right for your barrel length and pressure.
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