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O-rings

A place to ask general spud cannon related questions.
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O-rings

Unread postAuthor: K40T1C » Thu Mar 02, 2006 8:00 pm

Why do people insist on using O-rings in their pistons....

Oh wait how can I be so stupid... they make an airtight seal...

Correction... How can YOU be so stupid...
sure the O-rings make an airtight seal but what the hell is the point of that... a second ago you drilled holls in the piston TRYING to let some air through... and the friction caused by the O-rings would slow down the opening of the valve... costing you precious FPS
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Unread postAuthor: dragon finder » Thu Mar 02, 2006 8:08 pm

That is why you lube it up. So Correction how can YOU be so stupid.
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Unread postAuthor: saladtossser » Thu Mar 02, 2006 8:14 pm

mind being a little bit more polite?

a great seal between the pressurized air (both chamber and pilot) and the barrel is needed to prevent misfires!! the hole is so that the chamber and the pilot is equal in pressure.
using o-rings to seal a piston with a equalization hole means your gun can be more effecient.

on a chamber sealing piston valve, o-rings are a must!! the face of the piston is on the chamber, but what about the pilot? it will leak into the barrel if not sealed.
on a barrel sealing piston valve, o-rings are not needed, the face of the piston seals with the barrel. (edit: on a barrel sealing piston valve, equalization holes are not needed)

not much of a fps whore myself
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Last edited by saladtossser on Thu Mar 02, 2006 8:32 pm, edited 1 time in total.
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Unread postAuthor: dragon finder » Thu Mar 02, 2006 8:19 pm

Who me or him? If me sorry, if him please.
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Unread postAuthor: Shrimphead » Thu Mar 02, 2006 8:26 pm

O-rings can actually help the performance of a gun, if instead of normal equalization holes, you make them into one-way valves. Then when the pilot valve is actuated, no air escapes from the chamber.
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Unread postAuthor: dragon finder » Thu Mar 02, 2006 8:29 pm

Check out the 3" Piston topic that shows a one way pistion and how to make a 3" Piston.
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Unread postAuthor: CS » Thu Mar 02, 2006 9:10 pm

Shrimphead and DF: A sealing face was used to create the one way valve, not a o-ring.

This might seem like a echo of ST, but as he pointed out the o-ring in a chamber sealing piston is a must. Seeing as if air escapes around it, it will fire because this will leak air, then create a pressure difference, and then allow the piston to move out of the seated postion on the chamber. Yea I guess you dont to have any kind of a air tight seal around the piston on a barrel sealing piston, because it will equalize the pressure.

PVC against PVC cant make a very tight seal between its self. Thats why you use O-rings because of there "squishyness" (for the lack of a better term) that property allows it to fill in the imperfections of the PVC wall and to create the air tight seal needed on chamber sealing pistons.
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Unread postAuthor: dragon finder » Thu Mar 02, 2006 9:18 pm

I know what a O-ring and a rubber washer is I thought he said "O-rings can actually help the performance of a gun," ending the O-ring part and goung onto the rubber washer used for the one way valve and the seal needed.
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Unread postAuthor: Shrimphead » Thu Mar 02, 2006 9:27 pm

Ya, my post was kind of confusing. Dragon Finder got what I meant. When you have o-rings, and a one-way valve, it can increase the performance of a gun.
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Unread postAuthor: CS » Thu Mar 02, 2006 9:30 pm

Sorry if this has already been dicussed before, but I dont think it ever has because ive never heard a discussion on it...

Ok, I think by now every one here nows about the all-to-famous "supah" valve. This is a barrel sealing type piston incased inside a tee (any one caught on yet?). He could easy not use o-rings and use the space between piston and wall as a equlization point. Then if both surfaces of PVC were smooth and lubricated that would seriously reduce the friction of a typical piston. Plus it wouldnt have as much friction because there will be that little space of air also. Hmmmm I wonder... (sorry if you consider this hijacking your topic, but I belive you will find this discussion intresting, plus we pretty well addressed your original post...)

That would also explain his claim:
"Lubricated for life (as far as I can tell from testing)"

The thing that gets me though is that he has claimed to other people that he machines down to .001" or something. That perscion wouldnt be needed on a design that I speculated above. Here agian, I heard that kind of accurtness (is that a word?) would take extra time and a viberation free enviroment. Much less it wouldnt be required in a potato gun piston. Proably just saying that to give it the affect of being "state of the arc" type of impression. Makes me wonder...
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Unread postAuthor: boilingleadbath » Thu Mar 02, 2006 10:22 pm

Pimpmann, .001" is possible on any lathe that isn't a [20 year old] peice of crap.
The topic you where thinking of specified .0001", which is very hard to obtain.

And no, the piston (being multi-part) would leak out the sides and into the barrel.
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Unread postAuthor: dragon finder » Thu Mar 02, 2006 10:28 pm

.001 precision is very testy it woud have to be in a vibration free environment like you said i think breathing will trip it. In chemastry we have a balance that mesures to the .001 of a gram and if you walk by it it freaks out. I don't think that ammount of presision is easly possible or nesisary(sp?).
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Unread postAuthor: K40T1C » Thu Mar 02, 2006 11:32 pm

Ok wow i was asleep for tje last couple hours so sorry... anyways... I was mainly talking about coaxial valves.... i realize that you would nead to put a rubber washer or something on the fornt to seal the barrel.... and yes i do realize about the 3" piston thing but as i discussed i was just talking about using a mold and making something quickly out of plaster or bondo or sumtin... then just slap a rubber washer on it and wah-la... you got a pisston... something quick.... cuz i dont want to spend the time making that complex of a piston when a quick one could work almost as well
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Unread postAuthor: K40T1C » Thu Mar 02, 2006 11:40 pm

hey guys do you have any idea how much vibration a lathe creates... thats why they are so heavy... so that they dont move around from the torque...however they are by no means vibration free
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Unread postAuthor: Brian the brain » Fri Mar 03, 2006 3:33 pm

My gun does'nt use O-rings...and it fires pretty damn great.No misfires.

Check it out;
http://www.spudfiles.com/forums/viewtop ... 2&start=0&
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