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Diaphragm vs. 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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Diaphragm vs. Piston

Unread postAuthor: schismatized » Sun Jul 01, 2007 12:00 pm

how much better performance do you get from a diaphragm compared to a piston? diaphragms must be a relatively new trend because i never used to see them before i got back into the hobby a couple weeks ago. can anyone point me int the direction of some info on these? maybe some examples or a "how to"?
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Unread postAuthor: spud yeti » Sun Jul 01, 2007 12:06 pm

"Hi"(the member) just finished making a coaxial cannon that uses a diaphram as far as I know. Just go look in the pneumatics showcase area and its new the top. Ive only used a piston so far because I found them more logical :D
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really good quote/phrase here
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Unread postAuthor: schismatized » Sun Jul 01, 2007 12:14 pm

yeah i was looking at it and ive notice some people suggesting diaphragms over pistons. i cant see why though.. :?
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Unread postAuthor: hi » Sun Jul 01, 2007 12:22 pm

they open much much faster and dont need a bumper. the problem is that they have less flow than a piston. so it you have a relitivly short barrel, a diaphragm is better, but if you have a long barrel a piston is better.

a diaphragm is just a rubber piston. it works on the exact same principles as a piston. if you take the sealing face off a piston, you have a diaphragm. they also are much more secitive to pressure changes than a piston, so you can have a smaller pilot valve than you would need with a piston.
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"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
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Unread postAuthor: noname » Sun Jul 01, 2007 12:22 pm

Diaphragms are just so much easier to make and use. All you need is a circle of rubber. They also open much faster and don't require a bumper or a huge pilot valve. People say that diaphragms are better for short barrels, and pistons are better for long barrels, but I honestly cannot tell the difference (I used thhe same gun with both a piston and a diaphragm).

You can find a couple of mine in the wayyyyyyyyy back of the Showcase, or you can search NoName's Nade or Extreme Coaxial.
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Unread postAuthor: mopherman » Sun Jul 01, 2007 2:24 pm

noname wrote:Diaphragms are just so much easier to make and use. All you need is a circle of rubber. They also open much faster and don't require a bumper or a huge pilot valve. People say that diaphragms are better for short barrels, and pistons are better for long barrels, but I honestly cannot tell the difference (I used thhe same gun with both a piston and a diaphragm).

You can find a couple of mine in the wayyyyyyyyy back of the Showcase, or you can search NoName's Nade or Extreme Coaxial.

noname, are your phrams fixed in place? i always see them removed in your pics. can you just throw a peice of rubber in the gun?
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Unread postAuthor: noname » Sun Jul 01, 2007 3:25 pm

I mkae it so the edges have to bend so it fits tightly inside the pipe, then press the edges slowly until the diaphragm is up against the barrel. If that's "fixed", then yes.
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Unread postAuthor: mopherman » Sun Jul 01, 2007 3:30 pm

thanks, maybe ill use this on my small diameter coaxial. Cant get the freak to seal
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Unread postAuthor: hi » Sun Jul 01, 2007 3:50 pm

i think what he means by "fixed" is a diaphragm in a union, like mine. noname's diaphragms are not in a union, they are able to slide.
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"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
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Unread postAuthor: noname » Sun Jul 01, 2007 4:23 pm

They don't slide, because I extend the barrel through the chamber and partially into the female threads. The edges of the diaphragm are paartially in the valleys of the threads, and that holds it in place.
Let me see if I can find the diagram.....
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Unread postAuthor: PVC Arsenal 17 » Sun Jul 01, 2007 4:52 pm

Almost every gun I've made to date uses a diaphragm. They're easy to make and work great but are best for smaller guns.
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Unread postAuthor: schismatized » Sun Jul 01, 2007 8:03 pm

Yeah i think im gonna just use a 3" cap. my barrel is ten foot...
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Unread postAuthor: frankrede » Sun Jul 01, 2007 8:21 pm

noname wrote:They don't slide, because I extend the barrel through the chamber and partially into the female threads. The edges of the diaphragm are paartially in the valleys of the threads, and that holds it in place.
Let me see if I can find the diagram.....
Interesting.
I want to build a coaxial now.
so just a neoprene disk sitting on the barrel with a plug holding it down?
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Unread postAuthor: Pyro Ninja » Sun Jul 01, 2007 8:30 pm

Thank you "noname"...i finally know how to mount a diaphragm....Thank (you) :D
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Unread postAuthor: hi » Sun Jul 01, 2007 8:31 pm

schismatized wrote:Yeah i think im gonna just use a 3" cap. my barrel is ten foot...


do you mean a "quik cap", the rubber ABS end caps? if so, i recommend something else. i used one for my 2'' piston valve and it was to hard to seal properly. when it did seal OK, it was at about 140 psi. i recommend something else.
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"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
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