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Barrel Sealing Piston Cannon

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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Barrel Sealing Piston Cannon

Unread postAuthor: randompkguy » Tue Aug 07, 2007 11:12 am

Hey guys, I'm new here and I'm starting work on an over under type barrel sealing piston cannon. As this is only my second piston cannon I'm more than glad to take some advice. I'll try to post up pics as I'm going so you can all get a general idea of how its built on the inside. In the end I'm going for remote filling and firing for safety possibly using a C02 setup. Ive already modified a sprinkler valve for pneumatic actuation with a blowgun that I also modded for increased flow, and as if that wasn't enough, I attached an rc servo to the blowgun so I can actuate the pilot valve remotely. Pics will come as soon as my brother comes home with his camera...(Friday hopefully)
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Unread postAuthor: spud yeti » Tue Aug 07, 2007 12:44 pm

Sounds good, and I am looking foward to seeing the end product. How big is it going to be and what are you planning to shoot?

btw, I think this should have gone under pneumatic discussion area.
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really good quote/phrase here
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Unread postAuthor: randompkguy » Tue Aug 07, 2007 1:46 pm

72 inch chamber, full 2 inch porting, 2 inch by 84 inch barrel, with a calculated muzzle velocity of 500 ft/s at 90 psi with air (I used gas gun design tool).
It will shoot pvc darts, whole potatoes, bundles of glow sticks, and paintballs... as well as whatever i can find that will fit....

and ill repost in the discussion area as well, but shouldn't I keep this post up for all the pictures that will come?
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Barrel Sealing Piston Cannon

Unread postAuthor: randompkguy » Tue Aug 07, 2007 1:51 pm

Hey guys, I'm new here and I'm starting work on an over under type barrel sealing piston cannon. As this is only my second piston cannon I'm more than glad to take some advice. I'll try to post up pics as I'm going so you can all get a general idea of how its built on the inside. In the end I'm going for remote filling and firing for safety possibly using a C02 setup. Ive already modified a sprinkler valve for pneumatic actuation with a blowgun that I also modded for increased flow, and as if that wasn't enough, I attached an rc servo to the blowgun so I can actuate the pilot valve remotely. Pics will come as soon as my brother comes home with his camera...(Friday hopefully)
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Unread postAuthor: Modderxtrordanare » Tue Aug 07, 2007 1:57 pm

What exactly is your question?
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Unread postAuthor: turbohacker » Tue Aug 07, 2007 2:49 pm

Cool idea with the remote acuation, however what type of servo are you using?

RC servos dont move very fast and it will take a rather large one to move a blowgun.

Why not just use the RC speed controller to accuate the electric solenoid that is already on the valve?
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Unread postAuthor: randompkguy » Tue Aug 07, 2007 3:04 pm

spud yeti told me to repost in here from the showcase section, but i dunno why... anyway i do have a question now: i calculated that because of the pressure imbalance, there will be 398.7 pounds of force on the sealing face of the piston at 90 psi with a 2 inch barrel seal. Now is all of this pressure only on the rubber sealing face, or on the entire piston?
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Unread postAuthor: randompkguy » Tue Aug 07, 2007 3:08 pm

I put a weaker spring in the blowgun so that the servo is almost as efficient as my hand. Also if i used the stock solenoid the valve would open MUCH slower, but because this is a modded valve (the type with the blowgun on top) it will open very fast.

Also i can see you saying "why not use a longer tube to connect the blowgun to the sprinkler valve" the answer to this is that it will vastly decrease the flow of air exiting the valve (i tried it) and the way i have it allows for max flow and remote firing (up to 50 ft. which can't really be done with tubing)
Plus i might also make a stand with controls to aim the cannon, and i can use the rc remote to control those as well..
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Unread postAuthor: boilingleadbath » Tue Aug 07, 2007 4:08 pm

Sorry for the mess; I merged the two topics.

Indeed, spudyeti was correct; the "showcase" area is for <i>completed</i> cannons only.
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Unread postAuthor: randompkguy » Tue Aug 07, 2007 11:24 pm

oooh ok, well then....can i delete some of my repetitive posts somehow?
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Unread postAuthor: randompkguy » Fri Aug 10, 2007 3:48 pm

So I finally got some 3" pressure rated pvc tees and elbows from this plumbing supply place close to my house, but now I'm having an issue with my piston.

The inner diameter of the tee (which houses the piston) is a little less than a 1/4 bigger than the outer diameter of the piston, and I'm worried that because of this the front of the piston will not be square to the sealing face when pressure is applied (it would dip down a bit because it has no support)

So when i saw this, i put another rubber disk on the back of the piston (so that it fits in the piece of 3" pipe that comes into the tee, but the front of the piston still dips down.

The only solution that I can think of is to bring the barrel far enough into the tee so that it is almost flush with the 3" pipe, that way i can have the entire piston in the pipe. This seems like it would work but then I would lose a lot of power because that would restrict air flow to the barrel (it would have to make a 90 degree turn in the elbow, then another 90 in the tee, and then 180 degrees to get into the barrel, as opposed to just 2 90 degree turns if the barrel stopped in the middle of the tee....

so do any of you have any suggestions?

thanks.
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Unread postAuthor: randompkguy » Wed Aug 15, 2007 1:13 am

Hi guys..time to get raped by pics:

The piston:

Image
Image
Image

The grove where the washer with the spring sits:

Image
Image
Image
Image

Sprinkler valve, fill valve, remote firing setup:

Image

Full view:

Image
Image

Where it leaks:

Image
Image

Closeup of the remote setup:

Image

Any idea on how to seal the leaks? (already used teflon paste on the threads...failed..)
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Unread postAuthor: Modderxtrordanare » Wed Aug 15, 2007 1:36 am

randompkguy wrote:Any idea on how to seal the leaks? (already used teflon paste on the threads...failed..)


Use more, that's what I'd do. :wink:
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-How-To: Modding a Sprinkler Valve
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Unread postAuthor: spud yeti » Wed Aug 15, 2007 1:44 am

My ass hurts from that mega upload you just threw at me! :?
Other than that, it looks like one kickass cannon. Can you service the piston, or is it sealed in?
Oh yes, have you tested it yet?
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really good quote/phrase here
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Unread postAuthor: Modderxtrordanare » Wed Aug 15, 2007 1:59 am

spud yeti wrote:My ass hurts from that mega upload you just threw at me! :?
Other than that, it looks like one kickass cannon. Can you service the piston, or is it sealed in?
Oh yes, have you tested it yet?


As far as I can tell, the threads on it are so it can be taken out. :)
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