SpudFiles

Heres my design I came up with. If anyone here thinks it will work Ill build it tomorow and post it. Ive got all the parts cos im gonna take apart my harpoon gun http://www.spudfiles.com/forums/viewtopic.php?t=2014&, completely galvanized steel.

The concept should work, but keep in mind the area wich would normally be the pilot volume should be as big as possible as opposed to what would be desireble in a pneumatic.

You don't want the pressure behind the piston to rise too much.The bigger the pilot volume, the smaller the rise in pressure when the piston moves back.
You will need O-rings to ensure NO fuel can enter the pilot volume.Well...it's no longer the pilot volume but you know what I mean.

If pressure should build up on both sides of the piston, after ignition,you have succesfully made a handheld BOMB!!

Hmmmm, I might try to change my design then. Haha. I really want to make a hybride but do not want the fuss of burst disks. So ill try and improve on making a gun that is A) safe and B) easy to use (no disks).

Nice design, I would use a triggered burst disk if i were u but none the less.

There is one very simple change that would make that far more workable.

Link the piston via a threaded rod, to a small rubberized washer, which seals against a hole (washer on outside of hole) - which vents to the outside.

The piston gets moved back, the washer moves off the hole (being directly linked to the piston), venting the pilot volume - far more efficent.

It's a concept I've been bouncing around for a month or so, under the acroynm AVPTP (Auto Venting Pressure Triggered Pilot). I was planning to keep the idea back, but it could be several months before I build the damn thing, so I'm sharing it. It would also work for a normal pneumatic piston valve - aiding in the venting of pilot volumes (good for assisting blowguns)

This could also be coupled with my hybrid venting system from a while back on spudtech to further increase the potential.

Safety:

Endeavour to get the best seal between halves. Fill the "pilot volume" first, then fill the chamber seperately (from a Gen II tank if you want. You could make this the world's first semi-auto hybrid)

Accidents could be covered by adding a small replaceable burst disc/valve on the "pilot side". If a combustion starts on the pilot side, the disc will blow, preventing "a handheld bomb" effect. The seal would need to be good to prevent the pilot volume slowly venting - firing your mix in the process. (But it should blow in an emergency)

How does that sound?

The AVPTP, safety burst disc, hybrid venting system, Gen II tank, some form of reload, and you've got the world's most kick-ass cannon.

I had intended to do it myself, but haven't got the time, resources or parental permission.

No responses?

I thought my ideas were quite good and worth reading...

Gah, I'm misoverestimating myself again.

The self-venting hybrid valve a good idea, which is why it has already been done (by me).
I again was inspired by the DFTV by AKB.

Well, I'm pleased to say that I came up with the idea completely independantly.

Even if it wasn't original.

Damn.

Most of what we do has probably been at least thought of before, that doesn't make it any less cool
Sharing ideas is what the forums are all about, it's how the technology moves forwards. We have made great progress since the time I first got into spudding, about five and a half years ago.

My cannon does not have any mechanism to ensure the pilot volume does not combust, except that air is injected after the fuel and will flush much of the pilot volume from propane. If you make the pilot valve so that it opens as soon as the main piston starts to move, there shouldn't be a problem. For less strain on the piston and seals, you can do as I did and construct it so that the pilot valve closes again once the piston is fully open.

looks pretty good...

no reason why it wouldn't work bt be sure to keep the bottom of that piston coverd or it's gonna be blown off.