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problems with piston actuation

A place to ask general spud cannon related questions.
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problems with piston actuation

Unread postAuthor: Daemonseed » Thu Jan 11, 2007 12:14 pm

i have made a barrel sealing coaxial air cannon and the piston seals just fine, but when i pilot the air, the piston does not move back and stays sealed against the barrel until all the air is out of the chamber. my pilot is 1/4", chamber is 4" di., and barrel is 3/4" di. any help would be much appreciated thank you
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Unread postAuthor: CpTn_lAw » Thu Jan 11, 2007 3:36 pm

please send me a picture...i've had the same problem with my coaxial cannon.with the picture i can undertsand and help you
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Unread postAuthor: Bluetooth » Thu Jan 11, 2007 3:36 pm

The air might not be making it into the chamber and just staying in the pilot area.
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Unread postAuthor: jrrdw » Fri Jan 12, 2007 6:55 am

The air pressure in the pilot and storage chambers should be equil to each other after pressurizing the cannon, (DUH). My question is, doesn't the pilot chamber have to empty to the outside of the cannon? I ask because i'm not familur with the workings of a coaxial cannon.
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Unread postAuthor: CpTn_lAw » Fri Jan 12, 2007 7:42 am

there are two possible reasons.
1) Your pilot flow is too low.
2) your piston doesn't slide perfectly in the chamber.


The first problem's answer is try to increase the flow of your pilot valve, or try a smaller pilot volume, by decreasing the space behind the piston.
The second problem's answer is make your piston the much tighter as possible in chamber, grease the contact areas with the chamber, you have to make the piston to move without constriction, but without space between the cap or the neoprene (or whatever material your piston is made of)and the chamber walls.

PM me if there is still a problem.
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Unread postAuthor: Daemonseed » Fri Jan 12, 2007 11:03 pm

My piston is just a sanded 3 inch endcap inside the 4 inch chamber and the barrel end has a rubber coupling for the piston (endcap) to seat against. and there is about 2 inches of space between behind the piston. It does create a very tight seal with no leaks. Should i perhaps fill the piston so it is solid and drill a couple small equilization holes? Or just decrease the space the piston must travel? When the weather goes above 2 degrees i will be able to try it with maybe a 1/2 inch ball valve actuater.
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Unread postAuthor: noname » Fri Jan 12, 2007 11:14 pm

You're trying to use a 1/4" ball valve to fire!?!?! Just how optimistic are you? You'll need at least a 1" ball valve, I'd just go with a modified sprinkler.
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Unread postAuthor: Daemonseed » Sun Jan 14, 2007 7:56 pm

This is actually my first coaxial, if i can get the pictures to come accross my network id show you the pictures but other than that all i've really built are marble cannons. When it warms up i will try these suggestions thank you very much
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Unread postAuthor: Infernal2 » Sun Jan 14, 2007 9:56 pm

Yeah, I'm definetly going to go with "low flow" here. A 1/4 ball-valve is REALLY optimistic for a non-machined first gun. I'm working on getting mine to trigger with a push button micro valve but mine is all machined aluminum.

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Unread postAuthor: akaddis » Tue Jan 16, 2007 4:27 pm

use a sprinkler valve...it may handle less pressure but it triggers electrically much faster than your hand on a ball valve does...
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Unread postAuthor: Daemonseed » Tue Jan 16, 2007 11:41 pm

i would use a sprinkler valve, but the person who i am making it for wants to spend no more than 50 dollars, but he does however have a 1 inch ball valve. if it wasnt for these damn -5 temperatures i could acctually test it's operation.....I hate iowa
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