Triggered Burst Disk by Pilgrimman

[Pilgrimman]

Well, here she is:



The whole gun. I had to stand on a chair to fit the whole thing in!



The burst disk housing.



My personal favorite part, the protected schrader valve! (I blocked the flash with my finger, so only the red LED lit up the picture. There's no satanic rituals in my house!)

The only things I plan on changing are buying hose clamps for the hose, and building a barrel support.

Specs:
Chamber: 2" SCH 40 PVC 2'
Barrel: 3/4" SCH 40 PVC 6'
Other parts: Rubber schrader valve, 2 unions, 1/4 " hose, 1/4 " ball valve, and a blowgun.
Burst disks: Aluminum foil.
Operating pressure: 100 psi.
GGDT muzzle velocity: 656 fps.
Ammo: Glue sticks. Certain brands fit beautifully! They fit so well, that they can't be pulled down the barrel by gravity, but the slightest touch will move them! This makes for no blow-by, and virtually no friction! Best ammo I've ever found!
Loudness: LOUD! I had my MP3 player going full blast, and I could still clearly hear the burst at 35 psi! My parents only let me test it when they're gone!

Comments are welcome!

[blind909]

I dont get how you trigger it. can you explain?

btw, nice lookin cannon, just needs a little spraypaint to caover up those nasty purple primer stains

[MrCrowley]

He fills the cross with air so the pressure is the same on both sides, he closes the ball valve, triggers the blow gun which releases the pressure in the cross therefor making the pressure un-equal and bursting the first burst disk and then the second.

I'm not sure if you make the pressure the same in the cross, or slightly reduced so the second burst disk can burst easier.

Edit:

Nice cannon, though I would've made the stock part a bigger diameter pipe.

[Pilgrimman]

To trigger: Fill up the gun to half pressure or so. Close the ball valve. Now the part with the blowgun is isolated. Finish pumping up the gun. Now you have 100 psi on one side of the left disk, and ~50 psi on the other side. Then you let the isolated air (~50 psi) out through the blowgun. Since there is now nothing holding back the 100 psi in the rest of the gun, the left disk bursts, and bursts the right disk, and finally shoots the projectile.

Yeah, I was never good with primer. I'd rather be safe than aesthetically pleasing, but I agree the primer does look bad

[SpudFarm]

how does the blow gun empty the the "holding back chamber"? like instant or pshhh boom

[Pilgrimman]

Very fast. You hit the blowgun lever, and the projectile is instantly out the barrel. It makes the same sound as if you just popped a regular burst disk, and didn't trigger it. Again, the pilot is very fast!

[SpudFarm]

ok i mabe use this on my hybrid when it gets used as a pneumatic

[jrrdw]

Where did you get the idea to trigger the disk this way? Really cool set up, I'm impressed with the triggering set up! Now quick, enter the contest! 3 8) 8) 8) for you!!!

[Hubb]

I've seen the idea in the wiki but have never seen it on a launcher. A barrel support may be in order but this is nice. The only drawback I see is the loading time.

[DYI]

Nice. Believe it or not, the SCTBDC was originally intended as a handheld design similar to this... A barrel support and a larger bore could help power a bit, as could larger porting (just don't let your's turn into a monster like mine did).

And I think I might add this feature to my launcher, it could eliminate pumping altogether, taking chronic laziness to whole new and exciting levels

[Pilgrimman]

@jrrdw

The idea is not mine, (It's from the wiki), but my version is unique. I had the blowgun already, so I figured it could pilot ~5" of air sufficiently quickly. As to the schrader valve part, that's all me! 8) Thanks for the comment!

Edit: What contest? I didn't know there was one!

@hubb017

I do plan on building a barrel support, and you hit the nail on the head. This is a bear to load . It takes 2 min. on average. However, I did some testing after I posted the gun. The benefit in power far outweighs the loading difficulty. There is no hard data, but the difference is very noticeable. My old sprinkler valve gun achieves ~8 seconds of hang time (with a light projectile) at 100 psi. This gun achieves 6 seconds of hang time at 25 psi. I tested the gun with 40 psi, and the hang time was ~10-12 seconds!! The noise was unbelievable! My mother, who was inside the center of the house at the time, heard the pop! (I was outside)

To all: This gun is by far the most fun I've ever had with a spudgun! The most awesome part is: it worked first try! I thought there would be all kinds of complications, but it really is as easy as it looks! Literally anyone can build this! I'd encourage all pneumatic enthusiasts to build a triggered burst gun. It's easy, and very powerful!

Thanks for the input so far! 8)