Hybrid piston pilot valve. Your input please

[BigBang J]

O.K. I think I have got the idea now. Please let me know what you think of this design for a valve. The first design in the picture is the one that I am thinking of going with, I designed it first and I think is better than the bottom design. I started on the bottom design cause I thought that it was a good idea, but now I am thinking the top is better. I think it is pretty self explanatory but let me know if I left something out or you don't get something. So please give me your thoughts on this design.
O, I am going to be running a 7x mix, which I believe is about 90psi.

[Gun Freak]

I don't have input on the design, but I'm here to tell you that a 7x mix can generate about 700 psi

[BigBang J]

I don't have input on the design, but I'm here to tell you that a 7x mix can generate about 700 psi

Yes but I meant preignition pressures.

also one thing I am not sure about is the pop valve exhuasting of the pilot chamber. I mean will the pressure on the front of the piston force it back and start leaking out before the pop valve can open, or does it all happen so fast that it isn't noticeable? Also how do you calculate at what pressure the valve will open? I suppose you have to calculate the combusted gas pressure and surface area of the face of the piston that is exposed when sealed to the barrel?

[Gun Freak]

Have you seen SB15's piston hybrid? It is incredibly simple to understand, and after studying it for a minute you will understand how it works. I don't get how yours works, the design is sort of complicated.... Also I think the pre ingnition pressure of a 7x mix is 120 psi. 15 psi (atmospheric pressure) at 1x, 30 psi at 2x, 45, etc.

[Lockednloaded]

Have you seen fnord's early piston hybrid? Its extremely simple, but I'm not exactly sure how efficient in comparison to other valves

[MrCrowley]

Also I think the pre ingnition pressure of a 7x mix is 120 psi. 15 psi (atmospheric pressure) at 1x, 30 psi at 2x, 45, etc.

It's closer to 85-90PSI I believe (depending on where you live). At 1x, it is 14.7PSIA (PSI absolute) but really 0PSIG (PSI gauge). Then, at a 2x you start at 14.7 PSIG.

Not sure why we are still discussing this though.

[BigBang J]

come on guys, back on topic. I have studied SB15's piston hybrid, but I still don't think I quite get it. piston valves are new to me, before I just used pop valves. I am looking at fnord's early piston hybrid right now but he is using a pop valve design, which I was told and believe is not the best way to go.

[Lockednloaded]

did you look at the link i posted? it is essentially a giant pop-off valve

[BigBang J]

Yes I just finished looking at it. But was told that a pop valve was not the best way to go and over all a piston design seemed better and more efficient.

edit: The sequence is: The piston will start on the right side of the valve chamber, the incoming fuel mix will force the piston to the left side sealing to the barrel and opening the way to the combustion chamber through the check valve. The pressure will equalize between the pilot chamber and combustion chamber. So now there will be about 90psi behind the piston. when the mix is ignited the pressure will force the piston backwards which will increase the pressure and cause the pop valve to open and vent the pilot chamber. The piston then will be forced back and the gasses to go out through the barrel.

[saefroch]

This looks to me like just an overcomplicated version of a normal piston valve. Really the only addition over a normal pneumatic piston valve is the check valve connecting the pilot volume to the chamber, which could even be incorporated into a piston design.

EDIT: Blurred a little on upload... but I think this is more the design we discussed... am I wrong?

[ilovefire]

couldnt the mix behind the piston ignite when the piston is forced back even with the check valve it still might be able to build up enough pressure fast enough to ignite the mix?

edit: yes i think that that design would be safer because it doesn't have the fuel behind the piston as well

[SpudBlaster15]

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[BigBang J]

on the pilot area: I did not clarify something here, the propane will be introduced first, then the compressed air will come in behind it and force out the propane into the combustion chamber. So no ignitable mix will remain in the pilot area.

I don't think I quite understand the method of the pilot chamber in SB15's design. Can anyone enlighten me on that?

saefroch: EDIT: Blurred a little on upload... but I think this is more the design we discussed... am I wrong?
Ummm. I am not sure what you mean. I'll get back online lator if I can, I got to do some work now:)

[frocksie]

The second design in the first diagram is exactly what my piston hybrid looks like (<a href="http://www.spudfiles.com/forums/bolt-ac ... html">link here</a>). My launcher does not use a pop-off valve, for a few reasons. First, I'm not sure that a pop-off in a chamber sealing valve will really improve performance all that much. Second, the sealed pilot area acts is an air spring that slows the piston down, preventing it from impacting the back plug, and then resealing the piston. Finally, because the pilot does not need to be refilled from shot to shot, I can achieve a better rate of fire.

[SpudBlaster15]

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