SpudFiles

Simpler solution:
What if, instead of stuffing the potato in the ball valve, you put something light into the ball valve (empty redbull can is about 2") and that pushes the potato out of the barrel. The redbull can could be tethered to something on the gun to make re-launches easy. This solution would provide instant relief of all air pressure, be super easy to make, and (so far as i know) be the cheapest way to pneumatically launch a potato (well, 2nd to a ball valve without the can ).

theepicmool wrote:The redbull can could be tethered to something on the gun to make re-launches easy.

If it was tethered, it would also keep the air in the barrel and serve as a suppression device, a bit like this idea.

The theory sounds nice but in practice, that's one hell of a tether you're going to need

Not really, as long as it isn't being used a pneumatic ram (make gas vent from the barrel- i.e. muzzle brake before the tether works). If the piston is lightweight then there's no reason you can't use something like a braided fishing line.

inonickname wrote:If the piston is lightweight then there's no reason you can't use something like a braided fishing line.

Even for a light piston we're talking of a lot of force because of the velocity involved, not to mention the shock that is not the sort fishing line would encounter in normal use. You'd have to incorporate some kind of spring to spread the load over a longer time interval, and even then I don't think it would be feasible unless using low pressures and heavy projectiles that would keep the velocity low.

All this talk of silent shots and inner-barrel tethers are way ahead of their time at this point though, do you guys think my concept for the can-in-ball is solid in the first place? It doesn't necessarily have to be a can, just the first thing i thought of that was light, cheap and would fit.

@jackssmirkingrevenge's 2nd last
A short tether would be awesome as it would provide super silent shots. If I do use a short tether that keeps the can inside of the barrel then both the tether and can would have to be much stronger, and the can would need some sort of pressure relief to bleed off the excess air pressure after launch. Perhaps if the tether was just long enough to shoot the can out of the barrel about an inch, exposing an exhaust hole.

@inonickname
I'm not really sure what you mean, I would have to vent off air somehow, unless the whole thing leaves the barrel altogether.

i really cant see how the can idea could be simpler than a QEV, modded sprinkler or piston valve, it is a creative idea and if u could make it and it proves to be quite powerfull then job well done, but the complexity that i see is finding or making a tether strong enuff to with stand the force of the air behind it, and then u need to find a way to securely atach it to the can or whateva the object.

personally only having ever made a basic ball valve cannon myself, and after seeing the spudguns on this site it jst amazes me what people can make and what power they can get.

but good luck with makin this, i wuld love to see this in action if it all works out

Rather than a tether, some sort of sabot arrestor would be a better idea, chicken cannons can't be wrong

do you guys think my concept for the can-in-ball is solid in the first place? It doesn't necessarily have to be a can, just the first thing i thought of that was light, cheap and would fit.

It can't be a can really, you need something solid that won't be crushed in the period between there being pressure in the valve and it's not fully open. Solid means it's going to be heavy, so stopping it is going to be a bit of a chore. I would be much easier if you considered using solid projectiles other than potatoes.

I tried the tethered sabot many years back. This was with a ball valve cannon working on a couple of bar.
Failed almost every time, in spite of the sabot's light weight and the strong tether.

Personally, I can't get this obsession some people have with making ball valves less crap. What's wrong with just getting a sprinkler valve? Even if you operate it electrically you'll certainly see better performance.

@jackssmirkingrevenge
I agree. A redbull can is just the first thing i thought of that might work and would be light enough not to rob much power, but yeah, would probably get crushed. That being said, can's are pretty strong if the pressure on them is directed straight down, I'll bet you could get at lest one good fire out of a redbull can.

@Ragnarok
On the one you made was the piston stored inside the ball valve? Was the tether long enough to allow it to leave the barrel

@Ragnarok

Personally, I can't get this obsession some people have with making ball valves less crap.

Ball valves are the cheapest and simplest valves available, if they were more efficient they'd be the holy grail.

I agree with you all that the tether would be a chore if the can did not leave the barrel, but what if it did? In that case the tether wouldn't even have to be tied to anything on the gun! It could be tied to something outside, and it wouldn't have to be that strong considering how light the piston would be, at the point that its stopped there wouldn't be any air pressure behind it, and a light piston wont have much momentum.

Alternatively, if the can did stay in the barrel there could be a relief hole just behind the back of the can (when stopped). This would make any barrel designed for this have to be about 1/4 of a foot longer, but thats not a big deal for my purposes.

theepicmool wrote:On the one you made was the piston stored inside the ball valve? Was the tether long enough to allow it to leave the barrel?

No, the sabot was not stored inside the ball valve.

I tried running it both ways, both with a short tether (less than barrel length) and longer ones (longer than barrel by varying degrees) - both failed.

On the note of cost, to get a ball valve to equal the performance of a piston valve, you'd have to spend more money and time than it would have done simply to go with a piston valve from the start.
Doesn't sound like a holy grail to me.

Ragnarok wrote:On the note of cost, to get a ball valve to equal the performance of a piston valve, you'd have to spend more money and time than it would have done simply to go with a piston valve from the start.
Doesn't sound like a holy grail to me.

If done like this properly you have the potential for burst disk performance without the inconvenience of a burst disk setup, but again it would only work for hard uniform projectiles.

@jackssmirkingrevenge
Yes, the only reason I'm not is because the potato would get squished.

@Ragnarok
What part of a ball valve, some string and a can (or other piston-like object) would run me more then a piston valve?

If i need a piston that wont break (like the can might) I could just use some pipe with the same outer-diameter then the inner diameter of a 2" pipe (like the stuff the PVC Rockets are made out of on spudtech). I could cap it shut with some lexan or epoxy or something.

Moving on from a piston altogether, what if i were to use something along the same idea as a butterfly valve, but inside the ball valve. A-La This http://imgur.com/EVXrOl.png It would still be cheap to make using a small piece of lexan, a gasket and a metal pin.

Sorry for bumping, but I'm going to the hardware store soon, do you guys thing either idea would work? Nobody commented on my butterfly hybrid http://imgur.com/EVXrOl.png

You've already been told, it won't work. You need a strong projectile/sabot.

I don't get how the butterfly valve is meant to open.