Barrel Sealing Piston Cannon

[randompkguy]

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)

[spud yeti]

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.

[randompkguy]

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?

[randompkguy]

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)

[Modderxtrordanare]

What exactly is your question?

[turbohacker]

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?

[randompkguy]

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?

[randompkguy]

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..

[boilingleadbath]

Sorry for the mess; I merged the two topics.

Indeed, spudyeti was correct; the "showcase" area is for <i>completed</i> cannons only.

[randompkguy]

oooh ok, well then....can i delete some of my repetitive posts somehow?

[randompkguy]

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.

[randompkguy]

Hi guys..time to get raped by pics:

The piston:





The grove where the washer with the spring sits:






Sprinkler valve, fill valve, remote firing setup:



Full view:




Where it leaks:




Closeup of the remote setup:



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

[Modderxtrordanare]

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

Use more, that's what I'd do.

[spud yeti]

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?

[Modderxtrordanare]

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.