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PostPosted: Tue Jan 02, 2007 5:06 pm
by An Apple Pie
I am a little confused at what you are saying jetpilot. The valve will hold the mix back, and then it gets relesed. It has to pass under the spark, which ignites it, to get to the barrel.


PostPosted: Tue Jan 02, 2007 8:22 pm
by TurboSuper
This design would work very well for a portable hybrid, or mabye a portable propane/oxy gun (if you have the balls to "port" it that is[:p])

The absence of a burst disk makes it need alot less maiteneance between shots.

PostPosted: Tue Jan 02, 2007 8:40 pm
by Velocity
One minor problem that I see is actuating the piston valve. If you use a ball valve, you are too close to the hybrid (unless it is made of metal), and anyways, the exhaust would blow into your body and burn you.

A sprinkler valve would blow up (eventually, and it would be unsafe for the time). A QEV would probably bust a diaphragm

Actuated burst disks? Well that kind of defeats the whole point.

I was looking on ebay for an asco solenoid valve that would be able to handle such conditions. You could actuate it electrically, and remotely as well.

EDIT: I am NEVER going to post again [:p]:twisted:[:p]:mrgreen:[:0]

PostPosted: Tue Jan 02, 2007 10:00 pm
by LukeSkyRocket
Haha, 666 posts! HEy, thanks for the link to DR's stuff, btw.

So, Apple Pie, want to try it? I'd be all ears to hear how it turns out.

PostPosted: Tue Jan 02, 2007 10:32 pm
by clide
Triggering a piston valve by igniting the mix in the chamber without a vent valve would be pretty much the same as triggering a piston valve with a low flow pilot exhaust valve providing that the pilot isn't also ignited. What pressure it opens at could be controlled by the size of the piston compared to the sealing face or by the pilot pressure if the pilot is sealed off from the chamber. If you are really worried about how well the valve will actuate then a DFTV design like Galfisk used would certainly fix any problems that might arise.

I still fail to see how this idea is any benefit to hybrids. The valve will still endure the environment of a hybrid as the flame front travels back into the chamber.

PostPosted: Wed Jan 03, 2007 1:03 pm
by LukeSkyRocket
Clide: whether your analogy to a poorly-vented pneumatic is accurate depends on what kind of pressure multiplication you get when you ignite the fuel-air mix. I've got theoretical calculations that say the final pressure should be several times the initial pressure. If that's the case, I think this should operate fine. And if you are worried about pneumatic rebounding of the piston, I think a check valve(s) in the piston can solve that. I want to avoid the DFTV vent valve b/c all I have are a chop saw and a drill press, no lathe. Say, could a safety pop-off valve be pushed open from the inside by a small rod?

PostPosted: Wed Jan 03, 2007 3:54 pm
by clide
Well I probably should have clarified it, but my analogy was meant to imply that it should open fine, because a piston valve with a check valve and o-ring seals will still fire just fine with a very low flow exhaust valve. It loses some performance, but it still fires fine. And even though the final pressure is several times the inital pressure the piston valve could still be arranged so that it is opening around the peak pressure of the mix.

I wouldn't build a hybrid, but if I did I would build it with a barrel sealing tee valve with the pilot sealed off from the main chamber and filled only with air, that way I could try various opening pressures for the valve and see what works best. I probably wouldn't put any vent for the pilot, but I would leave room for an upgrade to the DFTV design if it needed it.

O-ring grooves are possible without a lathe if you are willing to get a little creative. I built several guns that used o-rings before I had my lathe, and I don't believe Galfisk had a lathe to build his hybrid.

PostPosted: Wed Jan 03, 2007 4:44 pm
by An Apple Pie
<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by LukeSkyRocket
[So, Apple Pie, want to try it? I'd be all ears to hear how it turns out.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
No not really. I mean my dad won't even let me build a combustion much less a hybrid. I really do not understand his logic. He will let me build a pneumatic that can fire over 1000ft, yet he won't let me build any type mon combustion. No propane/MAPP, no hairspray, no right/static guard, nothing.

Anybody have any advice for convincing my father? He said I could build one if I got a teacher from my school to help me, but I really do not want to do that.

PostPosted: Wed Jan 17, 2007 12:53 am
by PotatoNick
ha, you'd be helping the teacher most likely.

PostPosted: Sat Jan 20, 2007 12:04 am
by An Apple Pie
That is what I told him. My dad feels that I do not know enough about it, probably because he doesn't know and because he feels I am too young or something. I am not really sure. Anyways this teacher he wants me to talk to is a very smart high school physics teacher, but dealing with what I need to know he knows nothing. He might be able to give me some formulas or something, but I don't need them to make a simple combustion, or even a complex combustion. I know how to calculate how much propane to use and how to figure out the volume of the chamber and barrel, and that is about all that I need to know besides extremely basic plumbing/math.

What I find funny is that I am helping my friends build some cannons for themselves, I am on here helping some people get their project off the ground (this is in much thanks to people helping me). Yet I cannot build my own. I don't get it.

Okay I am done.

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