SpudFiles

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.

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.

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.

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.

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.

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

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.

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

You are correct. Here is the QCTBDC.

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

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.

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...

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.

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...

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.