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Clear Plexiglass Piston Problems. FIXED!!! WORKING GUN NOW

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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Unread postAuthor: Hawkeye » Tue Apr 10, 2007 8:18 pm

It doesn't look like the piston has much extra size over the barrel diameter. That doesn't give the air much area to push against. When you are putting a barrel into a T that isn't substantially larger than the barrel diameter, it can be beneficial to put a reducer on the end of the barrel in the T.
That does choke flow a bit but also allows the piston to activate easier and usually gives the piston a better sealing surface than just cut off pipe.
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Unread postAuthor: demilus » Tue Apr 10, 2007 8:21 pm

<<<<<<This is me right now!!!



If this didn't have swear words censored, I'd let loose a slurry that would make a pirate blush! I can't figure out what is wrong with this! I moved the barrel back, and it is now in the middle of the tee. I redid the piston so that it doesn't have any equalization holes though. But the piston doesn't make a f***ing perfect fit so air should go by fine!! It seals the barrel perfectly, but when I exhaust it, it just goes "fwoosh," really quick. It doesn't seem like the chamber is exhausted, but it is. I don't think it's my piston because I can move it just by blowing in one end or sucking on the end of the washer handle (which is really nasty by the way :x ). Any ideas now? Cuz I'm f***in lost.

EDIT: Thanks hawkeye, that sounds logical. Sorry if I seem dumb but this is my first piston and this crap just doesn't occur to me. Hopefully that won't affect performance much. I really think that's it. Dammit, stupid Kurt. I should've known better. (btw my name is kurt, it's not some friend :)
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Unread postAuthor: mopherman » Tue Apr 10, 2007 8:33 pm

try putting a slightly oversized rubber disk on the bacik to help the pilot air suck it back. use a skrew, not glue. its just faster
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Unread postAuthor: chaos » Tue Apr 10, 2007 8:49 pm

ok no1 take notice of what i posted and just repeat what i siad.

its all good.
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Unread postAuthor: mopherman » Tue Apr 10, 2007 8:50 pm

sorry mate, didnt see it
btw, does anyone know where killagorrilla has gone? he would normaly be all over this kind of thing
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Unread postAuthor: Hawkeye » Tue Apr 10, 2007 9:02 pm

Chaos ,sometimes while you are typing your response others jump in and you don't realize unless you check the first page of responses. Didn't realize yours was stuck on the end there.
Having said that I'm not sure your response was clear enough anyway. Not enough gas is getting around it is a bit vague. If you add an o-ring how won't that shut off flow around it altogether? Plus you struggled a bit with your own piston so....
It can be so easy to just make a simple piston properly. It seems that there is more interest in fancy cures than just simplifying the procedure in the first place.
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Unread postAuthor: mopherman » Tue Apr 10, 2007 9:05 pm

Hawkeye wrote:Chaos ,sometimes while you are typing your response others jump in and you don't realize unless you check the first page of responses. Didn't realize yours was stuck on the end there.
Having said that I'm not sure your response was clear enough anyway. Not enough gas is getting around it is a bit vague. If you add an o-ring how won't that shut off flow around it altogether? Plus you struggled a bit with your own piston so....
It can be so easy to just make a simple piston properly. It seems that there is more interest in fancy cures than just simplifying the procedure in the first place.

ok, how would you reccomend he fix this?
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Unread postAuthor: Hawkeye » Tue Apr 10, 2007 9:23 pm

I already did. Put a 1/2-3/8 reducer on the barrel seal. That will push the piston back even further which will keep most of it in its cylinder and allow more exposed surface area of the piston.
All that coupled with a natural reduction in pilot volume(from moving the piston back due to the reducer making the barrel further back in the T) should do the trick.
Of course these modifications could also result in a need to shorten the piston somewhat.
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Unread postAuthor: demilus » Wed Apr 11, 2007 5:43 am

I'm still debating on what I'm gonna do. I thought about the reducer but that's a lot more work. I've ultimately come to choices.
1)Get a larger tee and step up all the piston components to 1" (I have another plexiglass rod that fits perfectlyin 1" copper pipe :twisted: )

2)Go with what this gun was originally designed for and get a bb gun barrel, drill out a brass plug (which I already have), thread the gun barrel (I have a die cutter, yay owning a hardware store), and use the original piston design.

What do you guys think I should do?
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Unread postAuthor: spudthug » Wed Apr 11, 2007 5:51 am

bb gun barrel???dont waste a piston or plexi on bbs...use something useful..id go with number 1
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Unread postAuthor: chaos » Wed Apr 11, 2007 7:23 am

hawkeye ino it was kindof a joke, an yer killa still around he just doin stuff n hasn't had time.
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Unread postAuthor: lukemc » Wed Apr 11, 2007 7:23 am

i have this question that has been bothering me for awhile about piston vaulves and i thought id ask it before i make mine. if the pressur on both sides of the piston a equal the why when you point the gun up wards does the piston stay and not just slide back? i might be answering my own question here but is it because barrel causes a "suction" and holds the piston in place? and if thats so than why would you need a spring?
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Unread postAuthor: chaos » Wed Apr 11, 2007 7:29 am

nah it stays in ts place man, the pressure holds it there
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Unread postAuthor: cerberus » Wed Apr 11, 2007 7:37 am

lukemc, the preasure is the same on both sides of the piston but because the piston has a barrel on one side of it the force (force = area * preasure) is less on the barrel side or, to word it slightly differently, the preasure acts over a smaller area on the barrel side so there is less force on that side of the piston.
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Unread postAuthor: chaos » Wed Apr 11, 2007 8:58 am

ok this is a design ya mite have seen on here its mine and atm i dont have the time to build it so maybe you could do it out of Plexiglas instead of aluminum.

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