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Unbalanced spool valve for coaxial hybrids

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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Unbalanced spool valve for coaxial hybrids

Unread postAuthor: POLAND_SPUD » Wed May 25, 2011 2:41 pm

So this is just a slightly modified version of the system I am going to use. However this one does not use a detent - instead it relies on an unbalanced spool valve acting as the main valve. The spool itself acts as a bolt too so the gun is loaded from the breech

The barrel and the tube housing the bolt/spool are not the same ID - that's the essence of this design. A spring keeps the bolt/spool in closed position prior to firing. When the mix is ignited high pressure shuts the valve open and cycles the action
(the exact size of all the parts is yet to be determined)

So what do you guys think ?
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Last edited by POLAND_SPUD on Tue Sep 20, 2011 4:14 pm, edited 1 time in total.
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Unread postAuthor: wyz2285 » Wed May 25, 2011 3:24 pm

So when it ignits the bolt will be bushed back right? But how are you going to be sure that it will open? it's for a hybrid or combustion?
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Unread postAuthor: POLAND_SPUD » Wed May 25, 2011 3:49 pm

yeah, the bolt will be pushed back.

how are you going to be sure that it will open
It's an unbalanced spool. There is a surface area differential there and that's what is going to shut the valve/spool open when the mix is ignited
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Unread postAuthor: jrrdw » Wed May 25, 2011 4:45 pm

KABOOM, wheres the Earth shattering KABOOM? I think this will work, but how well is my question and, or, will the bolt/spool/valve tolerate the action???
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Unread postAuthor: POLAND_SPUD » Wed May 25, 2011 5:07 pm

but how well (...) will the bolt/spool/valve tolerate the action???

that's what I don't know. Obviously the oring that blocks the barrel will be exposed to high temperature.

I know that BUNA-N orings are good up to 250 F, Viton ones are good up to 450F. I also know that there are piston valve hybrids - if they can handle then why wouldn't this thing ?


The cool thing about this design is that you can use all sorts of ammo with it - both spherical non-spherical. Plus, it is a breech loaded coaxial, which is not something I've seen anywhere else.

It wouldn't be difficult to build a bolt action rifle around this system (and hopefully a true semiauto)
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Unread postAuthor: the unit » Wed May 25, 2011 5:31 pm

POLAND_SPUD wrote:I also know that there are piston valve hybrids - if they can handle then why wouldn't this thing ?

It wouldn't be difficult to build a bolt action rifle around this system (and hopefully a true semiauto)


I have yet to see a piston valve hybrid that was fired as rapidly as bolt action or semi auto would likely be. I would utilize a teflon seal and mated sealing surface.
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Unread postAuthor: POLAND_SPUD » Wed May 25, 2011 5:55 pm

Well I am hoping that purging the chamber with propane or butane will help to some extend

I would utilize a teflon seal and mated sealing surface
Yeah I realize that's probably the best option


I have yet to see a piston valve hybrid that was fired as rapidly as bolt action or semi auto would likely be
The thing is that no one has ever built a hybrid that can achieve high ROF so it's not that there were 999 attempts that failed due to overheating

I don't recall anyone attempting that
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Unread postAuthor: Zeus » Wed May 25, 2011 6:36 pm

Well first of all I'll suggest that you be rid of the spring and use compressed air instead. That'll make the opening pressure infinitly variable.

I hate to say this but this seems like a coaxial version of the rattlesnake valve. Good application though.
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Unread postAuthor: saefroch » Wed May 25, 2011 7:45 pm

Silicone o-rings are rated to 500F, and pretty cheap too.

The design has potential... but I'd like to see something work before I say too much.
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Unread postAuthor: jrrdw » Wed May 25, 2011 8:12 pm

Do you have a ready made spool to use or are you building one from scratch?
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Unread postAuthor: jhalek90 » Wed May 25, 2011 8:18 pm

where is the 3-way valve?

I assume it to be used for fule injection. haha.

The design, seems like it could work. the only problem i see is that in the event it does fail to open, the chamber will experience the full pressure of the combustion. (better make it strong!)
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POLAND_SPUD wrote:Anything is possible with the proper 3-way valve.
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Unread postAuthor: Gippeto » Wed May 25, 2011 10:37 pm

the unit wrote: I would utilize a teflon seal and mated sealing surface.


X2

As drawn, the o-ring will be blown off with the first quasi decent shot. Trust me on this.....happened with the hammer valve in my co-ax. :lol:

You COULD still use the o-ring, but you'll need to drill a series of holes from the spool face to the bottom of the o-ring groove. These passages will drain the pressure that builds in the groove, and keep the o-ring from blowing off. :) (cageless qdv anyone?:wink: )

THEN there's still the issue of temperature resistance. The gases in this case will bear more resemblance to a cutting torch....not o-ring friendly.

Sooooo.....What "he" said. :)
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Unread postAuthor: Technician1002 » Wed May 25, 2011 11:06 pm

Even non combustion air cannons have the issue with o rings blowing off. One of my early piston valves suffered that fate. It lost the o ring when running above about 35 PSI.

An extended barrel with with QDV style ports can be used to retain the forward O ring. An early unbalanced spool valve design of mine used the extended barrel and ports. It worked but the early design used a row of holes in the breech of the barrel so the flow was poor.

This early valve has a nose that extends into the breech of the barrel to seal past ports in the breech.
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Unread postAuthor: jackssmirkingrevenge » Thu May 26, 2011 12:01 am

hmm... isn't it basically just like a piston valved hybrid though? There's a pressure differential but a spring keeps it shut until the ignition causes an overpressure. The only difference is that your piston seals inside the barrel as opposed to the face sealing against the breech end.

Let's not stand on ceremony mate, let's see this POLSKA_HYBRYDA happen!
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Unread postAuthor: POLAND_SPUD » Thu May 26, 2011 12:08 am

The only difference is that your piston seals inside the barrel as opposed to the face sealing against the breech end.
naah, you can use both methods. The new thing is that it is breech loaded (not that there are any breech loaded coaxials that I know of)

I assume it is to be used for fuel injection. haha.
Yeah, I am predictable ;-)

EDIT
hmm I just realised that it might be possible to use metal to metal sealing alone (tapered spool/poppet). Even if it would be a bit tricky it is a viable option

EDIT no 2
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