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your thoughs on a big nasty

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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your thoughs on a big nasty

Unread postAuthor: Sancho » Tue Dec 21, 2010 3:33 pm

Hey,

I've made a ton of cannons over the years, from combustion to pneus, ball valves and sprinklers... i had an idea for a twin piston cannon... the goal is to shoot basically anything i desire, from 3" concrete slugs, to 1/2" bearings!

So i submit to you a pile of very bad MS paint sketches... let me kno if this will fly!

The second is a basic layout of the cannon... twin barrel sealing valves, 4" tank, to 3" barrel... both will be connected to the first sketch... which will fill evenly, and vent at the same time... and the 3rd pic, and idea for a piston... thinking about reinforcing it with steel...

Thanks in advance!

(pics went up in a funny order, sorry for the confusion)
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Unread postAuthor: metalmeltr » Tue Dec 21, 2010 3:44 pm

Looks like it would work, I'm no expert though.
May help to get more air down the barrel in less time.
I would recommend a larger pilot valve or and individual pilot on each valve, then link those to a single pilot, maybe 2, 1" valves piloted by another 1" valve (I say this because of the excess volume of pipe connecting the valves).
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Unread postAuthor: Sancho » Tue Dec 21, 2010 3:48 pm

so a 1" sprinkler on each valve, T-'ed to the fill line? makes sense, didnt know if i could get away with one... if i'm going overkill, might as well do it right... right!

Like this... green boxes are sprinkler valves, pink lines are Fill lines, then just hook the two sprinkler vaves to the same vent line
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Unread postAuthor: metalmeltr » Tue Dec 21, 2010 3:56 pm

Precisely
A 1" valve should pilot both no problem.
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 21, 2010 6:11 pm

Why the dual valves?

I'm expecting this reply :D

I'd wager you'd get the same performance with a single valve and some kind of restrictor at the breech to delay projectile movement, or a burst disk if maximum power is your ultimate goal.
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Unread postAuthor: metalmeltr » Tue Dec 21, 2010 6:49 pm

jackssmirkingrevenge wrote:Why the dual valves?

I'm expecting this reply :D

I'd wager you'd get the same performance with a single valve and some kind of restrictor at the breech to delay projectile movement, or a burst disk if maximum power is your ultimate goal.


Seeing as a valve that size would normally be piloted by a 1" i figure one per piston would provide optimum performance.
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Unread postAuthor: saefroch » Tue Dec 21, 2010 6:51 pm

In my personal opinion, the dual valves is excessive (if only because of the cost involved), but you might get slightly better performance. So long as the valve is not restricting flow with any orifices smaller in diameter than the barrel when fully open, the only performance gain is from when then valves are opening (which should be a very short span of time).
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Unread postAuthor: Sancho » Tue Dec 21, 2010 7:28 pm

cost isnt really a prob.... i work at a plumbing supply store.... cost pricing is a beautiful thing lol... we are a distributor for rainbird actually!

JSR.. Great link BTW... haven't seen that flick in years... tell me about this restrictor tho.... i know about burst discs, and never felt like they were something i would want in my projects.... is the restrictor similar?

My main goal in this was to use full lengths of pipe for various barrels (reinforced of course) to achieve some nasty distances/damages/other various reasons we all build this stuff..... 20' golf ball/spud/concrete/steel bearing/etc barrels

so my thought behind the dual valves was simply volume.... a 3" concrete slug, in a 15' barrel, it seemed to me, would benefit from the most air dumped at once.... but if the gains would be very marginal, i'll pass on it....

thanks for the input!
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Unread postAuthor: saefroch » Tue Dec 21, 2010 7:41 pm

3" concrete slug????? :shock:

Burst discs are the fastest valves out there, but can be a PITA to keep changing/replacing every shot. I think the restrictor is a good idea, rather like a detent.

If you work at a plumbing supply store and can access all sorts of fittings, why not build a piston valve of some sort?
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 21, 2010 7:47 pm

Sancho wrote:i know about burst discs, and never felt like they were something i would want in my projects.... is the restrictor similar?


This is the theory.

If you'll be using a 3" concrete slug however, as it's so heavy it will give the valve plenty of time to open fully before it starts moving. The benefit of dual valves on a short barrelled launcher with a light projectile would be visible, but in this case I'm sure it would hardly be worth the effort. Here's some GGDT modelling to illustrate the point, there is a performance gain for dual valves but it's not exactly doubling the power...
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Unread postAuthor: Sancho » Tue Dec 21, 2010 8:00 pm

jackssmirkingrevenge wrote:GGDT modelling


:twisted:

dude.... never has a chart like that, made me so happy lol

soo... i'm going to move a head with the single piston... i want heavy damaging ammo, in long a$$ barrels.... this thing may end up needing its own trailer lol

thanks for the advice everyone!
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 21, 2010 8:07 pm

With those specs I hope you have a safe testing area, consider how the predicted muzzle energy compares with typical rifle rounds.
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Unread postAuthor: Sancho » Tue Dec 21, 2010 8:12 pm

i live in Nebraska... i literally have miles of dirt/corn fields to "play" in... and this isnt my first round with these cannons... i've had the one close call years ago... no injuries, just some ringing ears... safety (relatively speaking) is my top priority... the chart is pretty handy tho
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Unread postAuthor: Technician1002 » Tue Dec 21, 2010 8:27 pm

A concrete slug has high mass. With the applied force, it's acceleration is relatively snail pace related to much lighter materials. A concrete slug does not require a really fast valve to dump all at once. A valve that opens in under 10ms should be fine. There is little benefit from a sub ms valve for launching concrete.

Save the HS stuff for low mass projectiles such as empty pop cans, foam sabots, and such.

Graph projectile position against time to see the effect of the mass.
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