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hybrid utilizing regular piston valve idea

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 utilizing regular piston valve idea

Unread postAuthor: POLAND_SPUD » Tue Apr 06, 2010 6:42 pm

ok so here is the idea.. build a regular piston valve pneumatic, add a metering system to it, pilot valve for the main valve etc.
then use either of the two to ignite the mix when the valve opens:

a mechanical mechanism using this -> http://en.wikipedia.org/wiki/Ferrocerium (which is powered by the movement of the piston)

or an electronic ignition system that activates for a couple of ms when the main valve opens (and the spark gap is either housed inside the chamber or in the dead space between the valve and the projectile)

I am not good at combustions and hybrids so forgive me if I wrote something stupid.. uhmm anyway what do you think?
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Unread postAuthor: Gun Freak » Tue Apr 06, 2010 6:51 pm

I seriously just had this idea about 5 minutes ago... I dont see why it can't work unless the spark doesn't ignite the mix in time. You'd have to time it perfectly. Probably have to be electronically controlled. Because if it don't ignite in time then your mix will just go away, then you'd have to refuel and fill and everything.
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Unread postAuthor: deathbyDWV » Tue Apr 06, 2010 7:50 pm

I think this has been mentioned before and the conclusion was that the projectile would be out too far before the mix ignites... I don't know though...
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Unread postAuthor: Gun Freak » Tue Apr 06, 2010 7:51 pm

Yeah that seems possible. Maybe there's a way to time it perfectly though.
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Unread postAuthor: POLAND_SPUD » Tue Apr 06, 2010 8:34 pm

I've been thinking about this and now I realize that the idea doesn't offer any advantages over a regular piston valve hybrid... anyway good that I noticed this before someone else :D

ohh btw I've spent some time modelling small hybrids in HGDT and I must say that I am quite impressed with what I found out...

50ccm chamber at 12X mix = 310m/s with 12.7mm steel BBs (that's ~402J)
I know there are a lot of problem with such small chambers but damn that's a lot of power...

lol I guess I could even build a semiauto hybrid since I've already have a lot of valves that can be used to automate the process... I know one thing for sure - I've got to think more about it
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Unread postAuthor: CS » Tue Apr 06, 2010 8:35 pm

1) Pre-combustion air/oxy-propane mix
2) Combustion

Why not use the differential of pressure of the two phases? Assuming you have a spring loaded piston and it can retain phase 1, but open in order of phase 2. Also having the spring adjustable via bolt might yield some fps, or so I will try.

This way you trigger the valve by the combustion itself, better order of events?

Have not saw a burst disk mechanism - automatic that is. Something like this.

^link^
4, would be one-half of a union (fixed). 5, would be the other half, spring loaded to create a seal. Rather then the belt ammo, a thin sheet of metal foil would be indexed between each shot.
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Unread postAuthor: deathbyDWV » Tue Apr 06, 2010 8:37 pm

Yeah I remember now that the other thread was discussing using a
ball valve... It would have opened alot slower...
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Unread postAuthor: ramses » Tue Apr 06, 2010 10:07 pm

POLAND_SPUD wrote:lol I guess I could even build a semiauto hybrid since I've already have a lot of valves that can be used to automate the process... I know one thing for sure - I've got to think more about it


I'll be starting mine after the ISEF...

I think you would be better off with a normal piston hybrid valve.
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Unread postAuthor: POLAND_SPUD » Tue Apr 06, 2010 10:32 pm

heh that's why I posted this...
I've been thinking about this and now I realize that the idea doesn't offer any advantages over a regular piston valve hybrid... anyway good that I noticed this before someone else

...one minute before cs comment suggesting the same :D

EDIT
anyway this is what I have in mind... I could have used a simple piston valve but I decided to move this thing a step forward in terms of simplicity and use JSR's valveless idea

not everything is included in this pic.. I omitted all the valves, meter and circuitry needed for it to operate automatically.. it seems that it's a better idea than the valve + loading mech that I proposed earlier... mostly due to the fact that it would be easier to machine and can offer better performance... so it seems that I might abandon that project
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automated hybrid.PNG
uhmm I hope you get it... there are no valves, meter and circuitry here... this shows only the most basic part of it... it could be either machined or built from standard fittings

how it works:
there is a spring loaded piston in the chamebr that vents the chamebr after each shot... as soon as the air cylinder retracts and loads new ammo into place the system is sealed (green in the pic is o-rings)... then the mix enters the chamber and forces the piston downward...
then the mix is ignited, ammo leaves the barrel and the piston is pushed upward exhausting spent gasses

the whole cycle starts from the very beginning
automated hybrid.PNG (32.78 KiB) Viewed 1181 times
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Unread postAuthor: CS » Tue Apr 06, 2010 10:54 pm

If you increased the surface area of the purple part, could you simply have it retract during combustion and reset by a adjustable spring? Getting the BB tube 2-3 diameters stroke behind the loaded position, so the piston (purple one) doesn't have to move as far, faster ROF.
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Unread postAuthor: saefroch » Wed Apr 07, 2010 10:02 am

This looks like a very interesting build to me, I only see a few issues with it. One is just balancing the clip spring with the air cylinder with the firing pressure with the attachment force of an o-ring with the size of ammo to the o-ring. Such a build would probably require a LOT of trial and error. The only other issues that I can see with this is your reloading piston. Depending on the firing pressure (before and after combustion) you'll probably have a lot of issues with heat buildup, o-rings sealing, and your reloading piston staying together.

I do have one suggestion for improvements on this though. If you can find a way to fill the chamber quickly enough (and I do admit that springloaded chamber is brilliant) you might consider trying to run the ignition system through the sealing head on that spring, thus providing an easy fully-auto firing mechanism, and easily calculable.

Just one more thing that you've probably already thought of is a valve to protect your expensive metering system. Other than that, I love the design and look forward to something being built.

EDIT: It also looks to me like this would finally provide us with a high-power automatic, which would be freakin' awesome!
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Unread postAuthor: POLAND_SPUD » Wed Apr 07, 2010 1:11 pm

I am mostly worried about valveless part of this design...
but even if I had to use a piston valve this thing can be built... from my point of view it seems as an easier route that building a 3000psi pneumatic

lol maybe becasue I've never built a hybrid before... I guess I would have to build some basic hybrids first

and I do admit that springloaded chamber is brilliant
If I remember correctly others have been come up with the same idea too... if you think of it it is the simplest way to vent the chamber
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Unread postAuthor: Heimo » Wed Apr 07, 2010 2:12 pm

Here is an idea to poke at...
how about a standard barrel sealing piston valve that is piloted with a pop-off valve.
here is my idea of how things may work.
at the moment of ignition the pressure in the chamber increases forcing the piston to move back this will compress the pilot volume and thus will the pressure rise causing the pop-off to vent and the piston valve to open
this is just an idea that I just dreamed up maybe you guys can poke a few holes in it cause I really did not put much thought into this.
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piston valve utilizing a popoff to vent
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Unread postAuthor: saefroch » Wed Apr 07, 2010 2:21 pm

This is a pneumatic, correct? Aren't we discussing a hybrid design?
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Unread postAuthor: Heimo » Wed Apr 07, 2010 2:40 pm

saefroch wrote:This is a pneumatic, correct? Aren't we discussing a hybrid design?


no, what I am suggesting is to use the regular pneumatic piston valve for a hybrid but use a pop-off to pilot it, cause I think the ignition will cause the piston to move back compressing the pilot volume and that will cause the pop-off to vent the pilot volume this will be a a type of piston hybrid . Have you read my previous post at all or are you guilty of ignoring text and skipping to pics
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