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Which of these three designs would produce best performance?

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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Which of these three designs would produce best performance?

Unread postAuthor: Chance » Wed Feb 10, 2010 12:33 am

Hey guys, I've been a lurker but decided to go ahead and create an account. I have O-rings and three ideas for a barrel-sealing piston valve; my question is which of these three designs would be the most effective in terms of flow co-efficient and opening time? Assume the vent port to be the same in all options. I'd just model in GGTD but I'm not quite sure how with the design.

In all designs the barrel is 2" and the back piston is 3" diameter and seals to the pipe--all but a small hole to equalize the vent space.

Image

In option 1 the front piston is roughly the same bore as the back--could use and o-ring to make the sides air tight, has sealing face to back of barrel.

Image

In option 2 the front piston is only slightly larger than the barrel bore and still seals to the back of the barrel, say 2.1" diameter.

Image

Option 3, the front piston slides inside of the barrel and seals to the sides of the barrel (with a floating O-ring, similar to Tech's design)

Any ideas which would work the most effectively?
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Unread postAuthor: spot » Wed Feb 10, 2010 12:36 am

Option 2 would be your best choice, Option 3 isn't going to work (Piston is going to get pushed into your barrel), and option 1 is choking flow from the chamber.
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Unread postAuthor: Gippeto » Wed Feb 10, 2010 12:50 am

Mr. Spot...is spot on. :lol:

Sry...couldn't resist. :)
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Unread postAuthor: Chance » Wed Feb 10, 2010 12:59 am

Thanks for the quick responses! Forgive the hasty drawings, assume that in option 3 we could put a forward stop on the piston to prevent the piston from getting pushed further in the barrel. Would option 2 still out preform it? Would moving the chamber further forward enough to allow the first half of the piston to go behind where it vents solve that problem? Assume that we could fix the simple issues in each design like that. Which would then preform the most successfully?
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Unread postAuthor: jackssmirkingrevenge » Wed Feb 10, 2010 1:02 am

Gippeto wrote:Mr. Spot...is spot on. :lol:


So you're saying that design has the best chance of success?

*sigh*

:D :D :D
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Unread postAuthor: tghhs » Wed Feb 10, 2010 3:38 am

Well, if your only option is what you've posted, then yes option 2 is your best beat.

Though if i were making your valve id have the barrel come right up to where the chamber goes off and use a solid piston. First this would mean that there would be no choke on the flow except for opening time and that a solid piston will be much easer to make and will have a less chance of jamming and breakage.

something like this. The important part is where the barrel ends. Preferably use a light material for the piston.

Also talke note of the pic at the botton of this thread, You will have to sand out the fitting to make a good piston that will work.
http://www.spudfiles.com/forums/first-p ... 20258.html
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Unread postAuthor: Brian the brain » Wed Feb 10, 2010 5:15 pm

You could round off the edges on the front of the piston to guide the flow to the barrel port.
( talking about the solid one)

You could use option two, but it will tumble.You need more length to the back piece to make it center properly.
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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