Burst disk idea

[fatcat]

I was going to keep this valve under wraps untill I could build a cannon with it but with the loss of a place to shoot, (I moved from the country into the suburbs) I will post it up here and hope someone can make use of it.

The main idea is a breech loading cannon with a burst disk valve. every time the cannon is loaded a new disk is put in. After the cannon is pressurized the disk would be ruptured with a spring loaded "bolt" with a point on it.

Here are some bad drawings done in MS paint

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The bolt is held back by a catch whitch could be released by a trigger or other device. A design like this would replace having to drop a pointy ended projectile for the barrel.

[pizlo]

The popular Nerfhaven clothespin trigger would give you a nice firing mech.
looking good, you could do it on a small sale to make a suburban gun.

[starman]

This design will depend on how much air pressure is being held back and how strong the burst disk is. If the disk is fairly sturdy, you'll also need a a fairly stout spring and sharp bursting bolt, obviously with enough power to overcome the burst strength the of the disk....possibly something along the line of a hunting arrowhead....that will cause large slits in the disk and hopefully more efficient air release than a simple puncture hole.

[Pilgrimman]

You could eliminate the flow restriction from the pin by mounting a sharpened paper clip into a slot cut in the barrel, and pop the disk by pulling the other end of the paper clip like a trigger. (Hard to explain). This seems like a good idea, though. The only problem I could see is that the pin might move around while you fill the launcher, and prematurely rupture the disk.

[psycix]

A punctured burst disk?

Make sure the disk wil actually blow and not just get a hole in it.
It will work.

Now you will just need to seal the hole where the bolt slides through.

[Maniac]

Yes frst ou have to have a way to keep air from leaking past the bolt.

[Hubb]

It will work. It's actually been done before. I can't find the link, or remember who built it, but it used a broadhead arrow head to do this.

The one problem you will have to consider is sealing the spike rod so that the pressure does not leak out around it.

[elitesniper]

I think it was gort who made it, he used a pneumatic ram with a broad head.

[Hubb]

You are correct. Here is the QCTBDC.

[SpudFarm]

i have wanted to look at the QCTBDC one more time forever but not found it thanks

[clide]

I also built something similar long ago http://www.spudfiles.com/spudtech_archi ... php?t=3802

Home built pneumatic ram is what did the puncturing.

The broad head would probably be a good idea, I had issues with my disks not bursting completely.

[Davidvaini]

I also bit a similar design for my compact grenade launcher.... thought it uses a trigger it still is the same concept of piercing the disk...

[fatcat]

A solution to air leaking around the bolt would be to have a plunger type thing fixed to the bolt so that it would seal when cocked back.

[FeLeX]

Hey Clide would you say that this type of valve is more powerful than a regular tee piston valve? I really want to make one but don't know how exactly I would build a ram...

[clide]

Really I couldn't say. I only fired it a couple times with a projectile and I didn't measure it or anything. My best guess would be that it is slightly more powerful than a regular tee piston. I'm just not a big fan of adding a burst disk each time so that's why I hardly used it.

Based on the picture of my piston I would say that the gun was made before I had my lathe, so it certainly can be done with common tools if you are willing to get creative.