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hybrid spring piston venting combustion chamber and valve

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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hybrid spring piston venting combustion chamber and valve

Unread postAuthor: BigBang J » Wed Jul 14, 2010 8:52 pm

I have been working on a design for a hybrid combustion chamber with a fairly simple venting procedure. I got the idea from CS's post, "spring piston exhausted hybrid chamber". I was also trying to get a good valve design without having to go with burst disks, as I would like this gun to be semi auto, or almost. I think this should be pretty self explanatory, I am running out of time so I can't go into detailed explanation right now.

your thoughts please.
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Unread postAuthor: chinnerz » Wed Jul 14, 2010 9:14 pm

I dono about semi auto...

...but this is looking good! I can't see any flaws in your design and it looks like it can be build in a day or 2

happy hunting
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Unread postAuthor: ramses » Wed Jul 14, 2010 9:25 pm

That looks good, but I don't understand why you're sealing over the breather holes for the piston. I don't see why they need to be sealed.

Good luck, you beat me to it!
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Unread postAuthor: jakethebeast » Thu Jul 15, 2010 3:31 am

thanks alot, this helped me very much with my new hybrid pistol.

looking good, i think this would work
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Unread postAuthor: CS » Thu Jul 15, 2010 5:52 am

Any details on your metering system?

On venting, I still see a sear catching the piston valve in the open position as the best option. What you've got here has only increased the theoretical dead space.

Also where is the mechanism(s) that make this more then a one shot deal?
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Unread postAuthor: BigBang J » Thu Jul 15, 2010 1:03 pm

Ramses, I guess the seal over the breather holes is not important, I just thought I would throw it in as an extra seal incase some how the piston seals leaked. But now that I think about it that may be a good indicator to let me know when to oil the piston.

CS, I have not completely worked out the metering system yet, but here are my thoughts. I was planning on having a regulator come off my propane tank to keep pressures consistent, then using a 3 way solenoid valve to control the metering. One port from the 3 way will go to the meter pipe, and when the valve opens from the meter port to the combustion chamber port, it will close off the supply. So 1 switch will activate that, then another regulator will come off my air tank to another solenoid valve, another switch will open this valve and will pressurize the chamber. Also I have thought about adding a rod to the piston that would pass through my spring adjustment bolt in the rear, and attach a sear/catch system there. But I have not got that far yet. I do realise that I do have a good bit of dead space, it would be nice if I could eliminate it. Still not sure if it is that big of a deal though. I wish I could come up with a valve with less dead space involved. Maybe I'll work on that some more.


"Also where is the mechanism(s) that make this more then a one shot deal?"

That is where the solenoid valves fit in, I am planning on having a pump action on this gun, again I have not worked out all the details yet, but this is what I am thinking. The pump will have several linkages attached to it and when pumped will activate the switches for the solenoid valves, first the propane 3 way, and then the solenoid for the compressed air. I would also like for it to control a bolt type reloading system for the ammo mag.


jakethebeast, glad I could help you! And I would like to see your pistol, I have been thinking about designing a pistol next.
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Unread postAuthor: ramses » Thu Jul 15, 2010 1:56 pm

your system seems workable, but I don't see where the ground is for your spark system. If you were planning on using a metal piston, that may work, but the oil between the chamber and the piston will act as a fairly effective dielectric.
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Unread postAuthor: BigBang J » Thu Jul 15, 2010 3:45 pm

I was planning on grounding the chamber, but you are right about the oil being a dielectric, I hadn't thought of that. A new thought, if I ground the chamber it will also ground the rear plug, the ground will then pass through the spring to the piston. Also,
The hot wire for the spark will run through the middle of the piston's guide rod, surrounded by an insulating material like ptfe or polyethylene, which will be inside of a piece of metal tubing which will be grounded. So in the drawing I should have put: conductor, insulator, conductor.
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Unread postAuthor: ramses » Fri Jul 16, 2010 12:53 pm

That seems workable. How do you plan to make connections?
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Unread postAuthor: BigBang J » Fri Jul 16, 2010 7:27 pm

for the ground screw I'll simply tap a hole somewhere on the chamber, probably in the rear plug and attatch the ground to a bolt there. I figured for he hot wire, I would use coax, strip off the outer jacket and use the inner insulator and conductor, and run that through the middle of the piston guide tubing. It would have to be a tight fit to form a seal. I am trying to think of a better way to do that part. Then the hot wire will attatch to the inner coax conductor that protrudes out the rear of the piston guide tubing, and just leave enough slack for the piston to operate correctly. I think what I will do for the hot wire is, I will drill and tap a larger hole on the face of the piston, then thread the OD of a piece of ptfe tubing, then thread the ID of the same tubing, thread a bolt stud into the ID of the ptfe with some loctite on it. More loctite will go on the outer threads of the ptfe tube and that will thread into the piston face and sit flush with the face of the piston. Aahhh! but then I need a way to attach the guide tubing without shorting to the hot wire. I'll have to think this out somemore, any ideas?
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