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Mattys Piston Problems,,"Inspired by Mr.Crowley"

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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Mattys Piston Problems,,"Inspired by Mr.Crowley"

Unread postAuthor: mattyzip77 » Sat Jul 23, 2011 10:13 am

I have recently tried to make a barrel sealing piston valve into a 2 inch T using a 1 1/4 coupler for the piston. I followed numerous different styles and directions found on spudfiles and guess what?? It does not work! It looks pretty much exacly like gun freaks piston used on his famous golf ball cannon. Now the problem is that the barrel will not seal. The piston will not even budge when I try to put air into it, via a compressor? I have tried switching things around, yelling at it, swearing at it, calling it names,researched on here, and still I cannot get this thing to seal?\.. Any suggestions how to make it seal??
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Unread postAuthor: Gun Freak » Sat Jul 23, 2011 10:22 am

Is your piston lubed? How tight is it? Is the seat perfectly square with the piston? Is the seat smooth? Is the sealing face clean? Pics help :wink:
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Unread postAuthor: mattyzip77 » Sat Jul 23, 2011 10:25 am

its not lubed, but there is enough room for it to move freely. yes all is smooth and square and clean my friend!! on yours I noticed you had a small hole drilled into your piston. what is this, is it the check valve, and do I need to do this??
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Unread postAuthor: Gun Freak » Sat Jul 23, 2011 10:27 am

Yeah it is a check valve but don't worry about that part. Can you take some pics?
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Unread postAuthor: Technician1002 » Sat Jul 23, 2011 10:59 am

If there is too much room for it to move freely, this often provides too much room for air to freely blow past the piston which may be the second issue after you get it to seal against the barrel. Too much piston blow by can make it refuse to fire. When you work on the piston, be sure to pay attention to both issues. Large diameter pistons are relatively difficult to get to work right and are often not recommended as a first cannon.

The space between the piston and the pilot wall needs to be very small.
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Unread postAuthor: mattyzip77 » Sat Jul 23, 2011 11:59 am

Tech1002 this is my first piston cannon, but like my 10th cannon overall. and gun freak the pics are coming, I cant find the mutha f@#%in cord for my camera :angryfire:
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Unread postAuthor: Technician1002 » Sat Jul 23, 2011 12:52 pm

I gave up on using the camera cord ages ago. I put a card reader in my computer. If I have not lost my computer, I know where the card reader is.
The larger the piston the more precise the valve has to be. Small leaks in a small piston are minor. Large unsealed areas on a large piston will present the problems you are experiencing. A tiny gap 1/8th inch long is ok on a small piston. On a larger piston it is easy to get a much wider gap that is much longer which will prevent sealing.
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Unread postAuthor: clemsonguy1125 » Sat Jul 23, 2011 2:08 pm

My laptop has a built in card reader, yours may too.
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That is all.
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Unread postAuthor: mattyzip77 » Sat Jul 23, 2011 2:59 pm

Hopefully this works guys. pics of piston are below
http://s1086.photobucket.com/albums/j451/mattyzip77/
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Unread postAuthor: Gun Freak » Sat Jul 23, 2011 3:33 pm

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Cut off the extra, it's only adding weight.
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NO IDEA why you did that.
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Extra DWV coupling used for nothing? Only increased pilot volume.
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Why such a small chamber port? It is limiting flow especially if you are using larger barrels, 1.5" and above for example.
Can we see the barrel seat? And why is that removable? Dude... you could have put both fill valves in that male adapter, eliminated the extra coupling, had less pilot volume, and glued in the barrel seat making it 100% safer...
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Unread postAuthor: mattyzip77 » Sat Jul 23, 2011 3:35 pm

well then, looks like i need to start over, shizzle!!!
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Unread postAuthor: Gun Freak » Sat Jul 23, 2011 3:41 pm

Well I say you start over too haha :D
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Unread postAuthor: saefroch » Sat Jul 23, 2011 3:55 pm

I feel I must agree with Gun Freak.
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Unread postAuthor: mattyzip77 » Sat Jul 23, 2011 5:30 pm

well apparently I screwed this up pretty good.you can never do enough research i guess!! back to the drawing board and back to the archives for more information. As arnold schwarzenegger said,"" I'll Be Back!!"" :?

And thank you gun freak for getting the pics posted for me, as I could only do it through photo bucket!! :D :D
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Last edited by mattyzip77 on Sat Jul 23, 2011 10:52 pm, edited 1 time in total.
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Unread postAuthor: Gaderelguitarist » Sat Jul 23, 2011 9:50 pm

Just don't come back with a few illegitimate kids, as the old Governator did....

Strip the valve down to what you need to make it work.

Piston: Needs to be cylindrical and have a perfectly square sealing face. Ideally light weight, and must be able to withstand impact.

Piston housing: Needs to allow the piston to move freely within and be relatively impact safe. This is done with the addition of a bumper to absorb the force of the piston.

No need for extra fittings or diameter reductions. I see WHY you tapped those two pieces into the piston housing, but that was not smart considering your piston must go there. I would simply use the tee and your female threaded coupling in concert, and then throw on a threaded bushing to which your pilot/fill valves will go. No need to tap into the piston housing.
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