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Burst disk PVC Cannon

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Burst disk PVC Cannon

Unread postAuthor: Immur4323 » Mon Jun 28, 2010 3:11 pm

This is my first post and my third air cannon. My friend and I made this for a history project while we were studying the civil war. Yes, our teacher was that awesome.

Anyway, it has a 46 inch, 1.25 inch barrel and a 2 inch by 44 inch air chamber. We also can raise and lower the barrel because we used pvc hose to connect the barrel to the action. I decided to try an new firing mechanism that I read about online; the piloted burst disk. If you don't know what that is there is a description. Sorry i posted the pics backwards.

I'm also going to make a piston cannon sometime. Does anyone have any suggestions as to of what type of piston i should make? Preferably something that doesn't require complex air seals.
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ppilot.PNG
Lets say the burst disk between both unions burst at 140 psi. You fill the pilot chamber with 80 psi and the air chamber with 160 psi. Because the 80 psi in the pilot chamber is pressing on the other side of the 160 psi of air chamber pressure it reduces the pressure on the burst disk making it only 80. When you let the air out of the pilot chamber with the pilot valve, it un-equalizes the pressure on the burst disk. Now there is 160 psi on a burst disk that breaks at 140.
ppilot.PNG (6.92 KiB) Viewed 2088 times
DSCN13n12.JPG
Here is a close-up of the firing mechanism.
DSCN13n12.JPG (39.11 KiB) Viewed 2088 times
DSCN1308.JPG
Here is the whole cannon.
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Unread postAuthor: Technician1002 » Mon Jun 28, 2010 4:17 pm

When the pilot area between burst disks is large, the energy goes down as this increases the dead space. If possible, make the pilot volume smaller.

Nice cannon. I bet it packs a punch.
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Unread postAuthor: jackssmirkingrevenge » Mon Jun 28, 2010 4:20 pm

Technician1002 wrote:When the pilot area between burst disks is large, the energy goes down as this increases the dead space. If possible, make the pilot volume smaller.


I think it's more the flexible tubing leading up to the barrel that is a bigger concern in terms of dead space, still, good effort.
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Unread postAuthor: spudtyrrant » Mon Jun 28, 2010 4:28 pm

nice job, but that hose is creating massive "dead space' between your valve and barrel, if you were to shorten it and increase the length of the barrel you would still be able to adjust launch but it would increase velocity substantially, or you could do away with it all together and elevate the whole cannon.
EDIT: dammit jack :?
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Unread postAuthor: SpudBlaster15 » Mon Jun 28, 2010 4:39 pm

The hose is creating a substantial amount of dead volume, but with such a large C:B ratio (~2:1), it probably won't have a very noticeable effect at the upper end of your operating pressure range. Still, I would attempt to shorten it at least somewhat.
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Unread postAuthor: Immur4323 » Mon Jun 28, 2010 5:40 pm

First of all, the hose is extremely thick. If I made it any shorter it would probably bend the barrel before the hose when I tried to raise it. Second of all, we didn't really write anything down on paper or try to find the best design; we just went with it. We knew we needed to put the barrel up front and make it so we could aim, so we decided on the PVC hose. Third, I put it in ggdt after we made it and figured that decreasing dead space to only a couple inches would hardly increase fps at all.
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Unread postAuthor: deathbyDWV » Mon Jun 28, 2010 5:41 pm

Good job. Is there any reason you didn't just mod a sprinkler valve? It wouldn't have been any more expensive... :?
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Unread postAuthor: Immur4323 » Mon Jun 28, 2010 5:47 pm

Actually it would have been cheaper. I figured the dual burst disks would have had a higher flow at a higher velocity than a sprinkler valve. And we wanted to test the idea. :D
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Unread postAuthor: kydavies » Mon Jun 28, 2010 5:57 pm

even a single burst disk of that size would be able to beat out a modded sprinkler valve and if you buy a PVC union it only cost 5-10 bucks (canadian dollars) vs 33 dollars+ the 10 bucks for the blow gun

anyways nice cannon, i rescently built a 2 foot long burst disk for marbles and nerf darts with amazing results
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mikemurph wrote:yea, the ammo has been changed to a more aero dynamic projectile. it consists of the back half of a dart, and a hot glue ball
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Unread postAuthor: jackssmirkingrevenge » Mon Jun 28, 2010 5:59 pm

kydavies wrote:even a single burst disk of that size would be able to beat out a modded sprinkler valve and if you buy a PVC union it only cost 5-10 bucks (canadian dollars) vs 33 dollars+ the 10 bucks for the blow gun


Technically you don't even need the blowgun, you can use the schrader you used for filling.
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Unread postAuthor: Immur4323 » Mon Jun 28, 2010 6:06 pm

With the blow gun there is a delay of 1 second from when I pull it to when it actually fires. With the shraeder it would be like 4. Besides the blowgun is nicer to pull.
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Unread postAuthor: jackssmirkingrevenge » Mon Jun 28, 2010 6:16 pm

With a tee having a ball valve on the end of it, you could attach the handle to a piece of string and have instant firing due to the much increased flow plus you have the authentic artillery effect :)
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Unread postAuthor: spudtyrrant » Mon Jun 28, 2010 6:33 pm

Immur4323 wrote:. Third, I put it in ggdt after we made it and figured that decreasing dead space to only a couple inches would hardly increase fps at all.
note i said decrease dead space and increase barrel length if you decrease the hose by 20 inches and increase the barrel length by 20 inches(replace the hose with a more flexible type such as vinyl so it is easier to bend) you will get about a 100-130 fps increase depending on the pressure. :wink:
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Unread postAuthor: Immur4323 » Mon Jun 28, 2010 10:59 pm

Yeah i guess I could have picked a more flexible hose I was just worried about it bursting.
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Unread postAuthor: kydavies » Mon Jun 28, 2010 11:22 pm

for your next burst disk gun use a ball valve then a burst disk (much safer) and yes i know there will be dead space but generaly safety goes first
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