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Piston concept question...

Posted: Thu Apr 10, 2008 10:46 pm
by THUNDERLORD
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?

Posted: Thu Apr 10, 2008 10:53 pm
by Lentamentalisk
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.

Posted: Thu Apr 10, 2008 11:08 pm
by THUNDERLORD
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.

Posted: Thu Apr 10, 2008 11:11 pm
by Gippeto
I do believe that JSR has used that on at least one project.

Found it;

http://www.spudfiles.com/forums/pneumat ... t7858.html

Posted: Thu Apr 10, 2008 11:14 pm
by jackssmirkingrevenge

Posted: Thu Apr 10, 2008 11:35 pm
by THUNDERLORD
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!!!

Posted: Thu Apr 10, 2008 11:55 pm
by Blitz
I kind of applied that concept to some of my break-barrel breeches. Works well if held solid.

Posted: Fri Apr 11, 2008 12:57 am
by THUNDERLORD
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.

Posted: Fri Apr 11, 2008 6:04 am
by biged
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///

Posted: Fri Apr 11, 2008 6:09 am
by psycix
Thats quite a nice piston setup biged!
Optimal flow if the porting is big enough and the space around the piston is too.

Posted: Fri Apr 11, 2008 7:58 am
by jrrdw
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.

Posted: Fri Apr 11, 2008 8:50 am
by rcman50166
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?

Posted: Fri Apr 11, 2008 8:55 am
by pat123
I have tried the silicon. it falls apart to easily for. It is really cheap so give it a try.

Posted: Fri Apr 11, 2008 9:00 am
by SpudFarm
Larda has a coaxial with a o-ring groove on the seat and a piston just out of plastic woth no sealing face.

Posted: Fri Apr 11, 2008 10:24 am
by DYI
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.