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no burst disc hybrid

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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no burst disc hybrid

Unread postAuthor: nabsnoabs » Sun Sep 24, 2006 2:02 pm

I was thinkin of this design for my first hybrid:

The gun would basically be a pneumatic and a cumbustion gun joined together with a sprinkler valve

In the rear, a chamber would be pressurized with air
the front chamber, which is connected to the barrel, would be injected with the right amount of propane to reach the resired fuel to air ratio

an igniter connedted to a spark strip would have a spark constantly running through this chamber, which would not ignite the gas because the concentrations would be too high
this eleminates the need to synchronize the opening of the valve with the sparking of the igniter

once the solenoid is activated, the valve is opened, the pressurized air hits the gas, and it immediately ignites

an alternative to this design would be another sprinkler valve between the gas chamber and the barrel to prevent any potential gas leaks prior to firing
its solenoid would be the same trigger as the first sprinler valve so they open at the same time and there is no need to worry about synchronizing

think of bein in a room and holding a lighter and sprayin aerosol over it
the room is full of air and ur sprayin fuel into it
now just imagine the opposite
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Unread postAuthor: Torch » Sun Sep 24, 2006 2:15 pm

Hmm this seems like a great idea. But you would need to dump the air fast enough so the air part wont ignite. Or is that impossible? *goes off thinking*
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Unread postAuthor: nabsnoabs » Sun Sep 24, 2006 2:27 pm

i figured that the air chamber wouldnt ignite because the pressure of the air rushing in would hold the propane in its respective chamber
once it ignites, the sprinkle rvalve would close to prevent backflow

i may have to rig multiple valves however to get a fast enough dump
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Unread postAuthor: Velocity » Sun Sep 24, 2006 2:31 pm

May work... I would NEVER use a sprinkler valve in a hybrid, no matter what it is for; maybe actuated ball valves would be another option?

Would the air rushing in mix well with the propane?

Anyways, considering that using a sprinkler valve between the gas chamber and barrel is an idea that should not be used, how would it actuate? Maybe some high-pressure asco valve perhaps... even then, the flow would suck.

If you didnt have a valve between the gas chamber and barrel, and kept a constant spark, it would be unpredictable, because say some fuel leaked out the barrel, then you have 8% propane in the chamber and BAM it fires (propane ignites between like 2% and 9% right? Or am I way off?)
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Unread postAuthor: nabsnoabs » Sun Sep 24, 2006 2:47 pm

ive been searching around online all weekend for solenoid activaited valves and most of them are way over my head when it comes to pricing

also its hard to find valves that can handle the potential pressures of a hybrid unless they are industrial grade

any ideas???
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Unread postAuthor: boilingleadbath » Sun Sep 24, 2006 9:20 pm

Protecting a cheap valve is simple: just put a check-valve in the air-inlet stream.

...but I don't think this will preform very well, considering how long you have for the fuel/air mixture to mix.
If you want to shoot 1 kg projectiles from a 2" bore (or simmilar), though, it might work out fairly well with the proper air-inlet geometry.
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Unread postAuthor: experament_u2 » Mon Sep 25, 2006 1:32 am

but think about if u time the activating wrong then everything could go horibly wrong and no more nabsnoabs (btw nice name :D )
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Unread postAuthor: GalFisk » Mon Sep 25, 2006 9:52 am

I remember posting a similar idea long ago, when the hybrid as it is was not yet invented. It could work if you get the air and propane to mix well as blb mentions. Injection through a capped coaxial piece of pipe drilled full of holes may work.
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Unread postAuthor: jrrdw » Mon Sep 25, 2006 6:00 pm

To many moveing parts in this idea for my taste, i'm interested in knowing how this would turn out. So if you build it, post it.
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Unread postAuthor: drac » Mon Sep 25, 2006 9:25 pm

DR already tried this and scrapped it. Not to shoot ya down, just saying it's been done before and the results weren't very satisfactory.
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Unread postAuthor: Jolly Roger » Tue Sep 26, 2006 1:36 am

I posted a reply a while ago about non busrt disk hyrbids. I was thinking about having everything the same as a piston exhaust pneumatic. It would work the same althought the only difference is, instead of releasing the pressure from the rear behind the piston, you could place multiple safety valves set to a certain releif pressure (eg. 100psi) and simply ignite the mixture with a spark strip in the primary chamber in front of the piston.. Heres a diagram, it should be pretty straighfoward. The trick would be to dispose of the pressure quickly enough so it wouldn't explode.
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Unread postAuthor: killagorrila99 » Tue Sep 26, 2006 2:00 am

Thats an interesting concept. :D
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Unread postAuthor: GalFisk » Tue Sep 26, 2006 3:42 am

And it works, too. See my <a href="http://galfisk.kaaven.net/gallery/thumbnails.php?album=17">piston valved hybrid</a> (which is not posted here because it's not yet finished). I've dry-fired it a few times, it also works well in pure pneumatic mode. The valve design is based on the <a href="http://www.qsl.net/wb6zqz/dftv19/">DFTV</a> by AKB.
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Unread postAuthor: Jolly Roger » Tue Sep 26, 2006 8:26 am

DUDE THAT IS AWESOME!!!! That is exactly what I planned on doing! What type of valve is the one at the rear? I'm using Rhino as well, just trying to figure it all out though thats all. Man thats mad, so the exhaust piston works by slightly pressurizing the air/fuel mixture in the area behind the piston upon ignition and then vents the air out of outlets just behind the small piston as it moves back a couple of centimetres?
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Last edited by Jolly Roger on Mon Jul 02, 2007 7:33 am, edited 1 time in total.
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Unread postAuthor: GalFisk » Wed Sep 27, 2006 5:26 am

The exhaust piston is connected directly to the main piston, so when the mix is ignited in the chamber, the pressure begins to move the main piston, which moves the exhaust piston and vents the pilot. When the piston is fully open, the vent is blocked off again which lessens the strain on the main piston.
The valve is a three way ball valve, which is modded so that it can point in any direction for fueling, pressurization or firing. It's also used as the trigger when firing in pneumatic mode.
I have a detailed (though somewhat obsolete) Rhino3D model of the gun if you're interested.
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