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Hybrid QDV Design

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 QDV Design

Unread postAuthor: saefroch » Wed Jul 07, 2010 4:05 pm

I've been thinking about how one could make a hybrid QDV... and I think this design will work, at least for low mixes. The spring will hamper the valve opening speed somewhat, but I don't think it will be much of an issue if the spring is for low mixes only, as it will only have to hold back a few pounds of force before firing, when the pressure should increase enough that it slides back cleanly.

Image

No, as I attempted to show in the picture, the two o-rings and the pipes they seal against are NOT of the same diameter.

Good idea with an air spring... I could pressurize the area behind the piston precisely to work for different mixes... that could allow me to access higher mixes.
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Unread postAuthor: c11man » Wed Jul 07, 2010 4:08 pm

not a QDV its a piston hybrid with a oring sea on the front instead of a seat.

otherwise it would work if you got the correct math with the spring pressure and area differences
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Unread postAuthor: saefroch » Wed Jul 07, 2010 4:09 pm

Okay, so if this is just a normal piston hybrid, please explain to me how it is not a QDV hybrid.
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Unread postAuthor: Hotwired » Wed Jul 07, 2010 4:12 pm

He's right y'know.

It's a barrel sealing piston.

But instead of dropping the pilot pressure you're raising the chamber pressure to move the piston back.
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Unread postAuthor: c11man » Wed Jul 07, 2010 4:12 pm

QDV has both seals the same size, you have different sizes and a spring
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Unread postAuthor: saefroch » Wed Jul 07, 2010 4:15 pm

Ahhhhh so that's the definition of a QDV... it's totally balanced just by the pressure. I have another idea then though... I'll draw it up and you can tell me it's just another barrel-sealing piston hybrid. :D
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Unread postAuthor: c11man » Wed Jul 07, 2010 4:16 pm

most likely :D
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Unread postAuthor: Hotwired » Wed Jul 07, 2010 4:17 pm

Make it the way you want it then worry about definitions of what's inside after :lol:
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Unread postAuthor: saefroch » Wed Jul 07, 2010 4:29 pm

Yeah... all the possible designs I'm thinking of would require some precision machining... making a telescoping piston would be tough for somebody like me.
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Unread postAuthor: Technician1002 » Wed Jul 07, 2010 8:50 pm

I have built that front seal for an air cannon once. You will need a new front o ring for each shot. They blow out of the groove and out the barrel in that configuration.
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Unread postAuthor: ramses » Wed Jul 07, 2010 9:15 pm

Does anyone know where my post went? You recognized the content, and no-one else posted that idea...

And the original post didn't' show an edit. Is this a new/double thread?
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Unread postAuthor: jackssmirkingrevenge » Wed Jul 07, 2010 9:30 pm

Hotwired wrote:He's right y'know.


:D
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Unread postAuthor: saefroch » Wed Jul 07, 2010 10:06 pm

Ramses, your original post is on the other thread. This is a new one, created for discussing the design.

I was thinking about the issue with the front o-ring blowing off... I might be able to attach the o-ring to inside of the gun itself, not the piston.

Yeeeeaaaahhhhhh.... even if it's not a hybrid QDV I think I'm going to go for this as the design for my eventual first hybrid.
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