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QDV Pumpkin Cannon Attention Technician1002!

A place to ask general spud cannon related questions.
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QDV Pumpkin Cannon Attention Technician1002!

Unread postAuthor: metalmeltr » Tue Jun 07, 2011 11:48 am

Could this be the next big thing at Punkin Chunkin?
Would a QDV piston that size be able to move fast enough to make the valve worth it?
I figure that the piston would have to be 10" in diameter to match the barrel. The I think you would end up with a piston about 12-14" long. At that size it is almost going to have to be hollow to move quick enough to do anything. So What do you guys think?
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Unread postAuthor: Lockednloaded » Tue Jun 07, 2011 11:54 am

I think it would destroy the pumpkin. IIRC, the valves on those guns are generally high flow, slow opening time valves coupled with large xhambers and barrels. The challenge usually is to preserve the pumpkins structural integrity for the duration of the launch
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Unread postAuthor: Technician1002 » Tue Jun 07, 2011 12:03 pm

Agreed with the summary. Pumpkins will want the first few feet to be relatively gentle on the pressure to prevent breakage while the pressure ramps up to full force.

As far as a hollow piston, if you saw my video on how the valve works, and the port sizes, and such, a solid piston made from light material would open fully in the same amount of time the pumpkin would move in the barrel a distance of it's diameter or two. Apple, or pumpkin, same relationship applies.

If the cannons I built were scaled up to pumpkin cannon status and kept the same relationship, the ports for a 10 inch barrel would only be 5 inches tall. Again see my video for the relationship of port size to valve size. 3 5 inch tall ports 10 inches wide would provide about twice the port area of the barrel cross section. This would permit a piston length in the 7 or 8 inch long range. The piston does not have to be longer than it's diameter.

To properly retain the o ring in that size, I would probably use many more ports. For 10 inch I would consider 6 ports 5 inches by 5 inches instead of 3 ports 5 inches by 10 inches.
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Unread postAuthor: metalmeltr » Tue Jun 07, 2011 12:15 pm

I think I have watch that video before. I'll have to watch it again. I was guessin og piston length on the basis that the pistons in your QDV cannons that I have seen are longer than their diameter from what I can tell.
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Unread postAuthor: saefroch » Tue Jun 07, 2011 4:33 pm

Launching pumpkins was discussed somewhat in detail here.
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