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CARV valve

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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CARV valve

Unread postAuthor: auxiliary » Thu Apr 09, 2009 9:54 pm

Hi, my project that I am about a third of the way done with is a semi-automatic (yes, one pull of the trigger one shot) propane combustion paintball marker. The design is like an enlarged blow forward bolt that is also used as an exhaust and fueling piston. Because I cannot create an exhaust valve that is attached directly to the piston, I came up with a valve that will let air through, but not hot gases from combustion through the same direction.

The CARV valve (combustion actuated reed valve) is an idea I came up with. It is a very thin rectangular piece of sheet spring steel that is curved upwards and covering a hole going to the outside of the chamber. The valve shuts when combustion of propane occurs, but does not shut when the piston returns to exhaust the expended gas. This works using the different properties of pneumatics and deflagration.

The valve does not close when the piston is moving toward it because it is not moving fast enough to create significant pressure and the air will just flow around it. It closes when combustion occurs because the ~80-90 psi generated by combustion along with a flame front will abruptly close the valve, sealing off the chamber. My question is, will this work?
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Unread postAuthor: sputnick » Thu Apr 09, 2009 10:10 pm

I would think that it could be made to work, that is essentially how the tippmann C3 worked, only instead of a reed valve or whatever it is called, it used a check valve, I think it would be very hard to find a material that closed well enough for a proper shot, but that would not close with hard pumping to purge the tank.

So yes, and no. It would work, but it would be a time consuming ordeal of trial and error to make just the pump work, much less the propane and air intakes you will need to perfect.
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Last edited by sputnick on Thu Apr 09, 2009 10:13 pm, edited 1 time in total.
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Unread postAuthor: King_TaTer » Thu Apr 09, 2009 10:12 pm

Ah OK, after my second time through I got it. Sounds pretty good just in a description. But I'm not an expert in bfb's. Theoretically it could work. As long as the reed has enough sensitivity to close and open when its supposed to. Also it will have to seal well during the combustion process and be able to withstand the pressure. I'll have to think about this some more before I post again and a picture might help. Good luck.
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Unread postAuthor: auxiliary » Thu Apr 09, 2009 11:36 pm

Here is a picture:

Sorry about not showing how the semi-automatic combustion operation will work. I don't want to release the design until I have tried it and know that is works.
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Unread postAuthor: psycix » Fri Apr 10, 2009 8:27 am

Or use some sort of valve that will pop closed when its suddenly subjected to a large load, but will let air through when the pressure is low.
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Unread postAuthor: auxiliary » Fri Apr 10, 2009 8:39 am

Yes, the valve uses your idea too psycix, so I will have to adjust how stiff the reed is (already it takes about .1 pounds to flatten it whereas the combustion will create ~7 pounds of force on it according to the surface area). The main idea that I think will make it work is that if there is air at 1 atm surrounding the reed valve and a piston gets shoved toward it, it will just manipulate the air to go around the valve rather than blast it shut because the gap between the hole it is covering and the valve is too far. Now if it is combustion, the flame front would be a quick concentrated burst of high pressure air that would slam the valve down.
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Unread postAuthor: ramses » Fri Apr 10, 2009 5:23 pm

why can't the bolt be connected to the exhaust? that would make everything much easier.
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