KAP-R3

[PCGUY]

<div align="center">KAP R3

Provided By - Andeh

My 3rd good PVC pneumatic. It uses pneumatically actuated burst discs, which I will go into more detail in a bit later. The air chamber is a 5' long chunk of 3" SCH40 PVC pipe. The main barrels I have are 5' 2.5" SCH40 PVC(not pictured) and 5' 3" SCH80 PVC(pictured below). The SCH80 is a perfect fit for pop bottles.

I had been wanting to build a more powerful air cannon for a while, and burst discs seemed to be a cheap solution. The only problem was that you don't know when the gun is going to fire, which isn't really something I like. Someone on the forums(clide maybe?) came up with a solution to this, which I feel I improved on. 2 burst discs are used for each controlled shot, to create a pilot chamber. This smaller chamber is connected to the main chamber via a 1/4" ball valve. Lets say the burst disc we're using bursts at 60 PSI. To achieve an 80 PSI shot, we simply leave the ball valve open while charging the gun to, say 40 PSI and then close the ball valve. Once the gun is up to the desired pressure, a blowgun that is also connected to the pilot chamber is depressed. When you do this, the pressure from the pilot chamber comes out, raising the relative pressure of the burst disc connected to the main chamber to the breaking point and bursting both discs. Hope I explained that well.

Some of the pictures on this page are pre-completion, with just the PVC, some are from NE Indiana Spudgun Event on 4/1/04.

Provided By - Andeh </div>

[sonicst0rm]

how loud is it?

[joemama]

i dont understand sorry

[julz]

joe, dont understand the burst disc thing or the question about how loud it is?

[joemama]

how he controls when it will go off

[CS]

He doesnt, but you have a pretty good idea after shooting it a will and what your using for the burst disk.

[K-Dawg-]

im thinkin about making a burst disk cannon what type if disk do you use aluminum foil , soda platic???
thanx

[nicholai]

LOL! look at the last picture, the guy is running away in the background ! funny stuff andeh

[dragon finder]

Heck I would too.

[drac]

How this cannon works is simple. You have two burst disks, with some space in between each other. That space is fill with air to counteract the pressure differential between the atmosphere and the chamber. So for an 80 PSI shot, you use a burst disk that bursts at 50 PSI, fill the chamber to 80 and fill the space between the burst disks with 40. When you exhaust that space, there is no pressure to keep the burst disk tear free, and it fires through that one and the second. It's an ingenious design.

[hannibal21]

So you actually don't need to pump it up to 100 psi for a 100 psi shot, right?

[spudshot]

yeah, you do, but if you want a 100 psi shot, and your burst disk wont hold that much, this system allows you to do that

[hannibal21]

Oh, I see. Thanks

[andeh]

Wow! Hard to believe there's still interest in this.

If you end up doing this, be forewarned-the discs leak since the unions are only designed to seal one way. I ended up having the unions milled so I could use another(thinner) o-ring on the other side and it worked fine.

To answer the volume question... too loud to NOT use hearing protection. Its rediculous.

And you can actually control when it fires, I have a blowgun which dumps the air in the small chamber. Since the burst discs themselves can't hold over a certain pressure(I use ~70 psi burst discs for a full power shot, notecards covered in duct tape-they're cheap and blow out totally. After you do it a few times its like clockwork.). So I keep the small chamber connected to the large3 chamber until it charges to around 50 PSI, and then shut off the ball valve that is connected to the main chamber. Fill the large reservoir and then fire.

[pipeguru777]

wow, thats a grate idea, bet it's a pain to use two burst discs tho.