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Troubleshooting piston valve hybrid

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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Troubleshooting piston valve hybrid

Unread postAuthor: Juggernaut12121 » Sun Jul 15, 2018 2:59 pm

After much delay I finally found time to finish my piston valve hybrid cannon, but after 4 attempts at a test fire I can't seem to get it to work.

I've went through and looked at all the joints for leaks (w/soapy water) at much more pressure than it would see post fuel and air injection and I can't find any. I'll have another run through later to double check though.

For my mixes I've been trying 4x and 5x mixes (2.4PSI propane and 44 PSI of air with a final pressure of 46 PSI as well as 3 PSI of propane and 59 PSI of air with a final pressure of about 60 PSI). I believe I have my pressures correct and my gauges are functioning as I've tried using my metering setup on my burst disc hybrid and it worked fine. Please correct me if those numbers don't look correct though.

My ignition setup has been acting up lately with the remote switch but 9 out of 10 times it works (I'll probably try and fix, or I may just rig something up that's a little more robust). The wires leading into the chamber don't seem to be shorting anywhere and the spark gap is set up just about in the center of the chamber.

My only guess is that the fuel-air mix isn't mixing well enough in the chamber? I tried letting it sit for a minute but it still didn't fire.

Any suggestions/ideas of what I'm doing wrong?
Thanks!!!
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Re: Troubleshooting piston valve hybrid

Unread postAuthor: jrrdw » Mon Jul 16, 2018 4:58 am

Can't these set ups work as piston pneumatics as well? Get the piston actuating first then add the mixes would be my advice.
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Re: Troubleshooting piston valve hybrid

Unread postAuthor: jackssmirkingrevenge » Mon Jul 16, 2018 5:56 am

What are you using for ignition and how big is your spark gap?

Does it fire at 1x?
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Re: Troubleshooting piston valve hybrid

Unread postAuthor: Juggernaut12121 » Tue Jul 17, 2018 5:25 am

I've fired it as a pneumatic a few times to test that the piston fits and the seals are good, for ignition I'm using a dc step up module similar to this one (https://m.ebay.com/itm/DC-3V-6V-to-400k ... 2522245188).
I haven't thought to try 1x mix, I'll do that when I get the chance.

Thanks!
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Re: Troubleshooting piston valve hybrid

Unread postAuthor: jackssmirkingrevenge » Tue Jul 17, 2018 6:07 am

Your problem might be too big of a spark gap, don't forget that it behaves differently as the pressure goes up.
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Re: Troubleshooting piston valve hybrid

Unread postAuthor: Juggernaut12121 » Tue Jul 17, 2018 8:52 am

I forgot to mention, my spark gap is around .5-1mm before I inserted it (I don't know of it shifted when i installed it). I tried filling the chamber with 90 PSI of air and it seemed to be sparking in the chamber (at least it was sparking off the leads going into the chamber).
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Re: Troubleshooting piston valve hybrid

Unread postAuthor: jackssmirkingrevenge » Tue Jul 17, 2018 8:58 am

Juggernaut12121 wrote:it was sparking off the leads going into the chamber


There's your problem?
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Re: Troubleshooting piston valve hybrid

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Re: Troubleshooting piston valve hybrid

Unread postAuthor: Juggernaut12121 » Tue Jul 17, 2018 4:58 pm

Oh no, I mean I have two leads coming out of the chamber for the spark gap, and while under pressure I connected one lead to one end of my module and then held the other lead ~1mm from the other end of my module to see if a spark would jump (as I assumed that it would mean I was getting a spark in the chamber).
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Re: Troubleshooting piston valve hybrid

Unread postAuthor: jackssmirkingrevenge » Thu Jul 19, 2018 2:16 am

Ah ok. Must be a mix issue then. Have you given volumetric metering a go rather than manometric or is the launcher too big for that?
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