burst disc air gun

[lasermaster3531]

This is my first air cannon to go on spudfiles, but it is not the first one I have made. This gun uses aluminum foil burst discs in a cascade-failure system with a blow gun pilot valve. the foil discs hold 20 psi each, and so far I have used two sets of three at a time for a total pressure of 100 psi. at 30 psi(two single discs) this thing will put a paper dart halfway into a cardboard box from 20 feet. it has a 1 1/2"x 15" sch40 PVC chamber, and a ~36" 1/2" sch40
CPVC barrel.
here it is.


this is the valve pulled through the end cap.


this is the main burst disc/blowgun assembly.


this is a close-up of the barrel adapter. it is a 1" PVC slip/thread union with a 1" to 1/2" CPVC adapter hammered into it.


here is one of the threaded unions unscrewed to show a blown burst disc prior to replacement.


here is the whole assembly unscrewed and laid out. I got the two threaded unions from our dysfunctional sprinkler system for free, but they would be $13+ from a store.


the whole thing cost me $25 or so to build, because I used so much"junk" from other projects. I recommend building one.

[Lockednloaded]

those are urls not img codes. But i looked at the pictures and seems to be a very cool little plinker. My burst disk gun is my favorite because of the simplicity. It almost never fails.
Good work on the triggered burst disks, i really like your set-up
P.s.
Your second disk is weaker that the first right (First from chamber)

[Marffy]

looks cool. probably would be a good cannon for airsoft. Try any nail darts?

EDIT: i got a good idea, put the bbs in between the 2 burst disks.

[inonickname]

Your second disk is weaker that the first right (First from chamber)

It's meant to be. The disks are tirggered by exhausting the gas between them, allowing the first disk to rupture (higher differential force) and then the second to rupture (as it is weaker).

probably would be a good cannon for airsoft. Try any nail darts?

Lol.

Kepp it up

[lasermaster3531]

the burst discs are the same. the space between the discs is pressurized to half that of the main chamber. when you exhaust the space between them(lowering the pressure), the rear one blows first, then the front one. there is a page on the spudfiles wiki.

[Lockednloaded]

I know, I have seen the wiki, and done quite abit of research on triggered burst disks. The second disk is actually supposed to be weaker, barely strong enough to hold the pilot volume this way air releases immediately into your chamber instead of all venting out of your exhaust valve

[lasermaster3531]

mine has them the same, but all of it goes out the barrel. the blow gun has such a small hole that it only lets through a small amount. this is helpful when the barrel becomes blocked or clogged, because the air will just go through the blow gun in a slow(ish) manner.
the burst discs in a triggered burst disc system are supposed to be the same pressure rating. here is a quote from the spudfiles wiki.
"The burst disks must be dimensioned to break somewhere between half and full chamber pressure. The trigger chamber is filled to half the chamber pressure, and then the chamber is filled to full pressure."
that means that both burst discs are rated at X psi. the space between them is at a little less than X psi, and the air tank is at a little less than 2X psi.
I don't understand how to put photos on here. can you help me?
what do you mean by img codes, i thought that you were supposed to put in the url of the photo at a photo sharing site.

[McCoytheGreater]

Pretty nifty gun you have. I really like the way these burst disk air guns work. Have you experimented with different layers on the burst disks to up the pressure in the chamber, or would there be too many variables to have to work out? I've never made a burst disc type gun, but would love to give it a try. They seem fairly easy. What's the difference in velocity versus a piston/sprinkler type gun?

[jackssmirkingrevenge]

Copy the image locaction and put that between [img] codes

Nice build, well made and with a bit more pressure probably capable of some very impressive damage.

They seem fairly easy. What's the difference in velocity versus a piston/sprinkler type gun?

Burst disk valves are probably the easiest and most effective valves to build in terms of performance. You effectively have a valve opening time of zero, instantaneous maximum flow, have a play with GGDT and you'll see the difference it makes

[Ragnarok]

... instantaneous maximum flow ...

Although the nature of that flow depends somewhat on how the disk blows. If it fails from the centre, then it folds outwards - and that can then inhibit flow around the edges.
If it fails around the edge, then the centre gets blasted out down the barrel, which can either damage the projectile or hinder flow around the fragments of disk in the air flow.

Burst disk valves are not quite as perfect for performance as some people would like to believe.

Ironically, the best option you can really have is a ball valve, provided you can find a way to open it in less than about a millisecond.

[lasermaster3531]

jackssmirkingrevenge, I tried to copy the image location, but I don't know how to do it. I know you all must think I am an idiot, but I am just new at this. I have right clicked on the photo, but there isn't an option that says "copy image location". there is one that says "view page source", one that says "copy image URL", and one that says "save image as...". I am new at this, so please don't call me stupid or anything. I am really smart(and modest,too!), but I don't see it.

PS.to all the people that asked about power, I have tried it with 3 burst discs in each holder at a total if 100psi, and this thing can hurl a paper cone dart about half a mile or more. once I tried a cone dart without any reinforcement like extra tape on the back end, and it just shredded the dart.

[jackssmirkingrevenge]

one that says "copy image URL"

This is the one you want

Then post as follows [img]image%20url[/img]

[lasermaster3531]

thanks! I will fix it right away.

[Lockednloaded]

I have tried it with 3 burst discs in each holder at a total if 100psi, and this thing can hurl a paper cone dart about half a mile or more.

That is highly unlikely, the 1/2 mile claim is often times made by those with bad guessing skills, or those who greatly over exaggerate performance. Unless you have a video or a ggdt file to back this up, don't say it. But again, great cannon.