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Another attempt at designing a Hybrid QDV...

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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Another attempt at designing a Hybrid QDV...

Unread postAuthor: saefroch » Fri Dec 31, 2010 4:34 pm

Series of diagrams showing valve actuation beginning at the point of ignition:

Image
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Image

Problems? Improvements? Suggestions? All appreciated, since I might actually be able to build this. :D
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Unread postAuthor: metalmeltr » Fri Dec 31, 2010 5:02 pm

I understand QDVs but i need an explanation on this one.
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Last edited by metalmeltr on Fri Dec 31, 2010 7:06 pm, edited 1 time in total.

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Unread postAuthor: DYI » Fri Dec 31, 2010 6:23 pm

The concept is valid, and as drawn it will work (although the seal at the forward bumper should be more substantial). But why? What could motivate you to put yourself through so much suffering to build a valve roughly equivalent in performance to SB15's design?

Seals in hybrid valves do not last indefinitely, and their life span will decrease as the mix is increased. I can't see the motivation behind adding in more of them, unless it's one of those "because I can" type things (which we all know I'm completely free of :roll: ).

Allow me to explain the concept for the benefit of those lacking a minute or two to work out the function from the diagram:

1. Chamber pressure rises, pushing back middle piston against pre-pressurised pilot volume and dragging center rod through forward piston
2. Rear piston passes vent hole, releasing pressure from pilot section and removing resistance to middle piston's acceleration (as in SB15's design).
3. Stop near end of rod catches front (barrel side) piston and pulls it back, opening the valve. This is further aided by the pressure differential which develops between the front piston's two faces after its front seal clears the breech (the volume behind it is not pressurised above atmospheric).
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Unread postAuthor: POLAND_SPUD » Fri Dec 31, 2010 7:06 pm

combine the main valve with the loading mech. (i.e. use a detent)

ohh btw where is jsr ? Is he in russia?/russian girl ?
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Attachments
automated hybrid.PNG
yeagh I know there is an air cylinder here but it should work with just a sping loaded bolt and/or bolt action
automated hybrid.PNG (32.78 KiB) Viewed 1069 times
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Unread postAuthor: saefroch » Fri Dec 31, 2010 9:30 pm

DYI: It kind of is one of this "because I can" things. In theory, I'm fully capable of building a hybrid, but I'd like to do something beyond a normal burst disc or piston setup, before I dump money on new parts, since I'm really not into large-bore stuff. Thanks very much for posting an explanation. I just slapped up the pictures and initial post right before I went off to a shortish party and was hoping people would be able to understand. I wasn't aware seals on hybrids wore out quickly, I'll be sure to take that into consideration. By "the seal on the forward bumper" do you mean the single o-ring I have separating the pilot side of the QDV from the chamber?

That automated hybrid has been around for such a long time (probably not, but it was one of the first things I saw on Spudfiles), I'm surprised nobody has built one. Probably something to do with the "automated meter and all that kind of things."

I do believe JSR is in Russia. He did a load of PUI right before he left, and I think I recall something about the country...
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Unread postAuthor: POLAND_SPUD » Sat Jan 01, 2011 4:26 pm

That automated hybrid has been around for such a long time (probably not, but it was one of the first things I saw on Spudfiles), I'm surprised nobody has built one. Probably something to do with the "automated meter and all that kind of things."

Our sponsors had (or have?) a gun with a 3way ball valve as meter... you probably know how it works right ?

anyway if it works with a ball valve you can adapt a poppet/spool valve to do the same job...
then just build a system that first actuates the valve injecting propane, then air and finally ignites the mix

sure it is a bit more complicated than a basic spray and pray combustion but I've seen dozens of more complicated projects on SF
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Unread postAuthor: saefroch » Sat Jan 01, 2011 4:44 pm

In my opinion, that's far more work than it's worth, though I've never seen a 3-way ball valve. Has anyone ever built an accurate automated metering system for a hybrid?
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Unread postAuthor: Lockednloaded » Sat Jan 01, 2011 5:24 pm

really all you need is a DCV, 2 low pressure regulators, and a couple of check valves. I tried to make one, but the regulator gave me hell. I just needed a higher quality regulator
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Unread postAuthor: saefroch » Sat Jan 01, 2011 5:53 pm

The problem I think you had is that you're trying to regulate withing a very small margin of error, simply too small for common equipment. I understand the theory and how it could be done, but it seems impractical. I'd rather meter manually and have a smaller error.
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Unread postAuthor: jackssmirkingrevenge » Mon Jan 03, 2011 5:52 pm

POLAND_SPUD wrote:where is jsr ? Is he in russia?/russian girl ?


Was in Russia, back now, and brought her with me for a couple of weeks. There she is in my bed and I'm catching up on spudfiles, oh the shame.
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