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Piston concept question...

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 concept question...

Unread postAuthor: THUNDERLORD » Thu Apr 10, 2008 10:46 pm

I was day dreaming about piston designs and how to make a good one and wondered,

The front of the piston is made out of rubber to seal against the barrel opening which is metal.
:idea: So being engineer minded I inverted that and thought what if the barrel opening had a rubber washer or rubber tube attached and the piston was all aluminum or plastic to be lighter :?:

Does anyone know about that, just never seen one like that. And I am wondering why not since in theory it would open faster?
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Last edited by THUNDERLORD on Fri Apr 11, 2008 12:58 am, edited 1 time in total.

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Unread postAuthor: Lentamentalisk » Thu Apr 10, 2008 10:53 pm

Yes that would work just fine. Generally piston weights aren't cared about to that extent, but it could be very useful in a piston hybrid where the piston hitting the back can sometimes kill your gun.
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Unread postAuthor: THUNDERLORD » Thu Apr 10, 2008 11:08 pm

Thanks for the reply Lentamentalisk,

It's not only the weight that would be improved but friction and that the rubber piece at the barrel opening could be constructed more "heavy- duty"
It just seems like a more sound design (if it works).

Maybe I could test a small scale version and use an aluminum gutter nail head (for the piston) with the spring around the body of it
and a pneumatic air hose tube cut of for the sealing face.
Mounted stationary to the barrel and one at the exhuast port.
Thanks for the advice.
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Unread postAuthor: Gippeto » Thu Apr 10, 2008 11:11 pm

I do believe that JSR has used that on at least one project.

Found it;

http://www.spudfiles.com/forums/pneumat ... t7858.html
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Unread postAuthor: jackssmirkingrevenge » Thu Apr 10, 2008 11:14 pm

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Unread postAuthor: THUNDERLORD » Thu Apr 10, 2008 11:35 pm

Wow, I feel stupid now,
I really didn't take the time to understand the pen gun or ever see the awesome video with schematic of your other gun.

Perhaps it was subliminal as I swear I day dreamed it up today.

One day very soon(maybe tommorrow) I am going to take the time to read every single post of yours.(I'll give you credit for whatever new ideas I learn).

Now you saved me from hours of testing a concept on something small scale I wouldn't really want. Thanks JSR and Gippeto.

Can't figure out why you never see that concept used more?
Like always, your designs are genius JSR. Spudfiles is Cool!!!
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Unread postAuthor: Blitz » Thu Apr 10, 2008 11:55 pm

I kind of applied that concept to some of my break-barrel breeches. Works well if held solid.
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Unread postAuthor: THUNDERLORD » Fri Apr 11, 2008 12:57 am

Well with these responses, I am sure I could make it work.

Thanks Blitz, I am trying to check out your creations but my security set-up is blocking the picture.

I'll have to look some more for one I can see.
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Unread postAuthor: biged » Fri Apr 11, 2008 6:04 am

Like this?
Image

I call it a linear coaxial piston.
Image
(Picture before it was all welded up.)

It's for a tennis ball bazooka.
Image
(Work in progress.)

///ed///
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Unread postAuthor: psycix » Fri Apr 11, 2008 6:09 am

Thats quite a nice piston setup biged!
Optimal flow if the porting is big enough and the space around the piston is too.
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Unread postAuthor: jrrdw » Fri Apr 11, 2008 7:58 am

Sounds kinda problem matic, sealing materail attched to the barrel could probly get sucked into the barrel more easly then having it on the piston.
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Unread postAuthor: rcman50166 » Fri Apr 11, 2008 8:50 am

Well since we're on the topic of piston valves, how do you guys think clear silicon window caulk would work as a seal? The stuff seems like a good fit. It's flexible, rubbery, cheap and comes in large amounts. Has anyone ever used silicon caulk for a seal before?
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Unread postAuthor: pat123 » Fri Apr 11, 2008 8:55 am

I have tried the silicon. it falls apart to easily for. It is really cheap so give it a try.
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Unread postAuthor: SpudFarm » Fri Apr 11, 2008 9:00 am

Larda has a coaxial with a o-ring groove on the seat and a piston just out of plastic woth no sealing face.
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Unread postAuthor: DYI » Fri Apr 11, 2008 10:24 am

Well yes, but larda's piston and sealing face are probably milled to such high tolerances that a conventional sealing face is unneccesary. Unfortunately, we don't all have that capability.

Butyl rubber makes an excellent sealing face material, but I don't know how well it would do used in an application like this.
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