SpudFiles

Dubya's WMD is currently drying. Its the gun I've been talking about for so darn long. Its got 2 4"x8' chambers ( 16' total) with a 20 foot barrel im putting on it later... ( Right now, its a 10' barell) Its a ball valve/burst disk setup being that the ball valve is released and the burst disk will rupture hopefully as soon as the ball valve is fully open. I'll have some pics up tomorrow. Man, I feel like a father waiting on the results of his newborns birth.... ( wow that was deep LOL) I'd like to thank everyone who helped! (Almost everyone) LOL :wav: :wav:

isn't hard waiting that 24 hours for the glue to cure? I always get antsy and do a low power shot a couple hours after gluing it. What size is the burst disk?

It may be a good idea to put the ball valve between the filling hose and the chamber instead. That way, there will be no flow restriction when the disk does burst.

2" burst disk. Not awsome, but it suffices

It sounds like a burst disk version of schmanman's SWAT. Can't wait to see pics or even a video of it!

It sounds like it will be really powerful and very fun to shoot
And just wait the 24hours I know that it is a painful wait but youll thank yourself.About a half a year ago I glued together my first pnuematic and followed the instructions on the can,cures in 2hrs if above 60degreesF.
Oh really I charged it up low power 1hr after I glued it and the end cap blew off the chamber at 25psi.
Post pics of this cannon as soon as you can.

Yeah, I got it up and tested today, but i need something a bit stronger than overlappiing aluminum foil... It bursts too darn fast... What would you guys recommend? BTW, IM gonna paint it all up hopefully this weekend and get it all looking good. Then I'll post some pics.

Who put it was a waste of money? and why do you think that? I'm interested to hear your explantion.....

How many layers are you using? In a 1.5" union, 16 layers bursts at roughly 160 psi, so if you use 16 layers in a 2", it should burst right around where you want it to.

mk
i was only using like at most 10
Thanks... BTW- my favorite video- ( its a safe video)

The surface area of a 1.5" disk is about 1.75", while a 2" disk is roughly 2.25" (these numbers are based on McMaster scale drawings and may not be completely accurate).

This means that a 2" disk has ~1.5x the surface area of a 1.5" disk, and therefore should burst at roughly 1.5x less pressure than a 1.5" disk, or ~100 psig.

Burst disks behave rather wierdly, as the burst pressure does not scale linearly with the number of layers, i.e. doubling the layers will more than double the burst pressure, although it usually takes hundreds of psi to notice this effect without very consistent disks.

And that means.....?
edit: Ok, I understand, but what do you propose i do? Like, an alternate disk? or how many layers of Al? 18?

Well I can't tell you for sure, but if you want the disks to burst at 150 in a 2" union, 24 layers would be the logical assumption (1.5x thicker). Due to the odd effect I mentioned in my previous post however, it may end up not bursting.

In my opinion, it'd be better to start at 16 layers and increase the pressure incrementally to find it's burst pressure. Then add layers until it doesn't burst at all anymore, and subtract one or two. Pressure testing burst disks is can be terrifying with bigger guns, but it is a necessary evil for the best possible performance. Just be thankful you're not turning the dial on a regulator and watching in disbelief as the pressure climbs over 400 and the disk still hasn't burst, and there's ominous creaking noises coming from somewhere...

What pressures is your compressor capable of?

that sure sounds like the mega cannon i made a year or too back. trust me, its plenty powerful with a ball valve. i had a 1.5'' barrel though.my recommendation is make a fitting that you can screw on and off so you can shoot at different angles. (i.e. 45 degrees and 180 degrees.)

A while back I read about someone useing aluminum cans for burst disk. I have no idea what it takes to bust it, probly a good bit more then foil.