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Cannon in progress.

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: Hotwired » Mon Jan 22, 2007 4:39 pm

I don't know why theres always a post or two about dead space when its minute compared to the very large quantity of pressurised gas that'll be dumped in it on firing. Dual sprinkler valves will flood that space in way less time than could be humanly noticed.

I think its a decent design.

On the subject of using a ball valve or blowgun to pilot the sprinklers I saw an interesting valve the other day which I posted on UKSGC to suggest for piloting large piston cannons or large QEV assemblies.

It looks like an oversize blowgun at 3/8" instead of 1/4" and thats with 3/8" female threads at both ends, not 1/4" at one end and 1/8" at the other:

http://www.airlines-pneumatics.co.uk/webcat/Detprod.asp?ProductCode=s07010750

It is however a UK store but you might be able to find something similar where you are.
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Unread postAuthor: Pneumatics » Mon Jan 22, 2007 5:27 pm

MrCrowley wrote:
Pneumatics wrote:
noname wrote:There's also DWV elbows, I'd worry about those more.


hmm, no i think there schedule40 elbows. i could of sworn the box they were in said they were.


Isnt Sch40 just the thickness?


o, now i see. so maby they are thick but not socket depth. thanks, im learning alot of info on these forums


and i got a question what do u guys mean by dead space?
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Unread postAuthor: MrCrowley » Mon Jan 22, 2007 5:32 pm

Dead Space - Dead space is the space between the projectile and the valve. The closer the valve is to the starting position of the projectile the less dead space there is. That further away the valve to the projectile the more space there is that the air from the chamber needs to fill in order to reach the projectile and launch it, Thus wasting precious air and pressure.
Some people don't mind it others do, Just next time you build your cannon keep the valve as close to the projectile as possbile.

And on the topic of DWV, if you spend enough time here at spudfiles you can pick out DWV from pressure rated parts without looking at the writing on the pipe, you can judge the thickness,the shape,the socket depth and the piece of pipe to determine if it is pressure rated or not.
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Unread postAuthor: Hotwired » Mon Jan 22, 2007 5:33 pm

Its the space the compressed air has to fill before reaching the projectile.

So in your case its the tee joining the sprinkler valves and the barrel. It is not compressed and its after the valves and before the projectile in the barrel.
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Unread postAuthor: jrrdw » Mon Jan 22, 2007 5:45 pm

Why not use another sprinkler valve to vent the two you need to vent? Just use some garden hose to join it all together, that will be about 1" woth of venting, and the hose will be strong enough. My friend Willard uses it at his shop for a air line at a constent 120psi.
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Unread postAuthor: medievalman » Mon Jan 22, 2007 6:10 pm

That might be kind of expensive. You can get a ball valve for $5-10 while a sprinkler is $15-20. It would increase performance a little bit, but you probably wouldn't even notice it. I don't think that spending an extra $15 would be worth the extra 3 fps that you might get.
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Unread postAuthor: noname » Mon Jan 22, 2007 6:28 pm

Sch 40 is the thickness, not the pressure rating. The elbows have shallow sockets, and you can feel that they are much lighter compared to a regular pw elbow of the same size.
Where'd that second page come from?
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Unread postAuthor: Pneumatics » Mon Jan 22, 2007 7:03 pm

o thats what dead space is. I couldnt of done anything diffrently to eliminate the dead space I think because I needed the T and I needed the 2 1"threads
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Unread postAuthor: Hotwired » Mon Jan 22, 2007 7:11 pm

Its nothing to lose sleep over when its that small compared to your resevoirs.

When its something like 25cm of empty pipe then you shouldn't let it off the drawing board. I've seen some 'sniper' rifles that force the air all round a hollow stock before it even reaches the barrel. Theres just no need for that kind of dead space.
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Unread postAuthor: tylerthetatertosser » Tue Jan 23, 2007 12:37 am

cool gun!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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