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... I need serious help with a 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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... I need serious help with a piston...

Unread postAuthor: Amos » Sat Nov 11, 2006 3:28 pm

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Okay, Here's what I've got so far.

4" pipe for the outer compression chamber, 3"-2" reducers sanded down and pounded in and glued into the 4" pipe, and a 2" barrel on the inside.

I need to know how to make a piston for this...

I've got a way to pressurize the chamber, and a way to pressurize behind the piston...

I need to know what I can use as a piston that will work...

I've tried a shaved down 3" endcap... but air leaked all around that...

some one please tell me.

Edit: I'm also using tire fill nipples... is there something I should be using instead of these?
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Unread postAuthor: jrrdw » Sat Nov 11, 2006 7:55 pm

13 views and you guys couldn't help him out? I remember when i first joined, a lot of post then were what to make pistons out of, you all got your answers!

Amos-sounds like you need a rubber sealing washer on your piston face that seals against the barrel, i use one the same size as the piston, cut down to the piston diameter, about 1/8 inch thick. Bolted to piston face with 1/4 bolt and nut and flat washer, i used JB Weld to seal the bolt leaks. The piston should have small equilization hole, to allow equal pressure in chambers.

A good place to start research is spud wiki, link at top of spud file page, great info there for about every question you can think of, let us know what happens.
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Unread postAuthor: MrCrowley » Sat Nov 11, 2006 7:59 pm

i think he's asking what to use as a piston as the 3" end cap leaks
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Unread postAuthor: schmanman » Sat Nov 11, 2006 8:01 pm

did you put neoprene on it? take it off / get a new endcap, then put a 2 inch fernco rubber coupler (ask the guy at the store) on the barrel where the piston presses against it,inside the gun.
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Unread postAuthor: squeaks » Sat Nov 11, 2006 8:12 pm

the problem is probably that your filling it with that tire vavle. It wont let the air in fast enough to seat the piston. use a ball valve and a quick connect instead.
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Unread postAuthor: schmanman » Sat Nov 11, 2006 8:23 pm

from the diagram, It looks like you are putting air in from the side of the piston, and that could be the problem (If that's the schrader valve on the side, next to the gauge), because the air would not force the piston forwards, and the air would leak around the piston and out the barrel.

EDIT: oh, stupid me :oops: . I see it's on the back, but then what's that next to the gauge?
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Last edited by schmanman on Sat Nov 11, 2006 8:25 pm, edited 1 time in total.
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Unread postAuthor: jrrdw » Sat Nov 11, 2006 8:24 pm

I use a shrader valve, "tire valve" and have no problem with the piston not sealing. I use a sprinkler valve to operate my 2" piston valve, so in fact i'm sealing two valves with the shrader valve. I just think that it would be easer to fix the piston thats allready made. By adding a rubber seal to it.

EDIT: To fill it from behind the piston would make it better.
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Unread postAuthor: Amos » Sun Nov 12, 2006 1:10 am

It fills behind the piston, and infront of it...

My understanding of this is you create a greater pressure behind the piston, then fill up the expantion chamber... then to fire, you release the pressure out of the piston's chamber, causing the expantion chamber's pressure to push the piston backwards and out...

If I'm wrong.. please tell me..

aswell -- If you could draw a diagram.. it would be very helpful.

As for the spud wiki:

"Error - 404

Wrong/missing page.

Please report what page your comming from and what page you are trying to view by emailing me.

Please check your spelling of the URL and links.

Please go HOME."
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Last edited by Amos on Sun Nov 12, 2006 1:15 am, edited 1 time in total.

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Unread postAuthor: killagorrila99 » Sun Nov 12, 2006 1:14 am

No, You need a really small hole in the piston to fill up the chamber. It doesent matter if air leaks around it, It should still work.
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Unread postAuthor: Amos » Sun Nov 12, 2006 1:15 am

killagorrila99 wrote:No, You need a really small hole in the piston to fill up the chamber. It doesent matter if air leaks around it, It should still work.


How small are we talking?

Pin sized, or 1/16th drill bit sized?
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Unread postAuthor: Amos » Sun Nov 12, 2006 1:18 am

killagorrila99 wrote:No, You need a really small hole in the piston to fill up the chamber. It doesent matter if air leaks around it, It should still work.


... Oh.. wait a second I think I see what you're talking about.

It doesn't matter if air leaks around the piston into the pressure chamber... just aslong as there's a seal on the barrel?

I'm not looking to charge this thing up super high.. It's going to be used as an airsoft mortar.. so we wont be seeing pressures higher than 50 PSI...
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Unread postAuthor: MrCrowley » Sun Nov 12, 2006 3:37 am

squeaks wrote:the problem is probably that your filling it with that tire vavle. It wont let the air in fast enough to seat the piston. use a ball valve and a quick connect instead.


as long as you fill it fast enogh with enough pressure e.g using a air compressor you will be fine.
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Unread postAuthor: jrrdw » Sun Nov 12, 2006 7:29 am

I reported the wiki being down, shame you got that 1st time looking, but it happens to the best of websites from time to time.

I made my piston from wood, used a two step hole for equilizeing the pilot and storage chambers, from the back of the piston the hole is 3/16th", and from aprox. 1/8th" to the top side of the piston it's 1/32nds", (i was attempting to meter the air flow from the storage chamber back into the pilot chamber when fireing). The less air escaping back into the pilot chamber, the better your piston will work! Some members here use check balls in thier pistons, (that lets no air back into the pilot chamber when fireing).
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Unread postAuthor: Amos » Sun Nov 12, 2006 2:02 pm

Is there a way you can get it to work with a 3" endcap?

because that's what I've bought haha...
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Unread postAuthor: jrrdw » Sun Nov 12, 2006 4:12 pm

Yea, bolt a rubber washer on it for a seal, like i suggested, fix the one you got.
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