Double Sealing Piston Cannon

[Greihawk]

This is my idea for a piston cannon that seals on the back face when valve is operated, hopefully resulting in very little pressure loss from the main chamber. I am going to build this gun in the next couple of weeks and try it out, any comments or criticisms in the meantime are most welcome.


Please forgive the paint drawing, i was at work when i came up with it. And, also if anyone has tried something like this before, could they let me know of any problems they might have faced.

[boilingleadbath]

Is that to scale? If so, I'll point out:
The diameter of the piston-movment-tube is smaller than that of the barrel, meaning that there won't be enough force to "pull" the seal of the barrel. Make it bigger.

[Greihawk]

sorry, should have put that it wasn't to scale, i drew the piston 1st and then pasted it in, the piston guide tube will be 3 1/2" and the piston itself will be machined out of 4" aluminium bar, i drew the pic the way i did so that it would be easier to understand the principles.

[longshot1068]

forgive me sins and my ignorance on this but how does this get vented to actuate the valve? if i had to guess i would say that it would be from behind the stem of the valve via a mechanism such as a blow gun or sprinkler valve?

[Greihawk]

yes it will be be via either of those, to start off with a blowgun, until i have tested it and seen if its any good.

[longshot1068]

lucky guess, ive only built one cannon and it was a combustion.

[Greihawk]

i got thinking about Boilingleadbath's earilier comments and came up with this as a possible way around it, let me know what you guy's think, as i am not to sure myself.



When the chamber is being filled the ball bearing moves forward and the spring stops it from sealing the other end. when the pressure is released via blowgun(or other) the air release sucks the ball on to the sealing face. This creates a closed system allowing the full pressure of the chamber to act on the large barrel sealing face, pushing the piston backwards

[Greihawk]

I forgot to add that for a 2" barrel you would need the large piston face to be about 3", this way the surface area of the piston surrounding the barrel is greater than the size of the barrel.

[saladtossser]

a check valve wont help, u need more surface area in the back, or risk accidental firing.

[Dragon_keeper]

Wow im lost. How do you get the gun to fire? If there is enough force to keep the seal air tight then wouldent it take a lot of force to pull the plug off of the barrel? Sorry if i sound stupid but im REALLY new to this whole spudgun thing.

[saladtossser]

i'll point u in the right direction:
http://gbcannon.com/flash/coax.swf
http://gbcannon.com/flash/barrelseal.swf
http://gbcannon.com/flash/chamberseal.swf

copied from that topic in spudtech so u dont have to sign up
darn html wont work
to get the edit screen of somebody else's post, copy and paste the post or topic id and forum id to find the original code the poster used, thats how i got those links, just in case some1 think i'm up to no good.

btw, who owns gbcannons and when will it be done?

[BT1969]

I would think a flap valve would be a much simpler alternative to the spring and check ball. It would be easier to get a good, tight seal also.

[zeigs spud]

WOW 6 posts and somthing nice has come out. lol i rally like this idea for ver very mini's mabey? it's a god idea but i think to save time most would just use the regular piston valve cannon disighen. nice idea though i really like it!