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Hybrid test results.

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 test results.

Unread postAuthor: Fnord » Sun Sep 16, 2007 12:12 pm

The results are finally in!

As most of you know, I built a sealed hybrid vessel recently to test the limits of 2" sch40 steel.


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(more pictures will be posted on request, be specific though)


I finally got around to testing this earlier today.

Final test results: Inconclusive!!

That's right, I could not cause a failure in the test hybrid with the pressures I could reach. I may continue testing if I ever build a high pressure pump.


Test specifications to take note of:

Chamber volume: 750 ML
Chamber material: 2" diameter sch 40 galvanized steel. approx 12" long
Ignition: camera flash+ignition coil
Fuel: Propane/air
Single spark gap, centered.
Chamber obstructions: significant
Temperature: ~63F in the shade


Initial/starting test mix: 5x 60psi
Final test mix: 11x ~160 psi



NOTE THAT I DID NOT DRILL INTO THE CHAMBER to create a spark gap. I drilled into a smaller pipe nipple and added a significant amount of jbweld to ensure a good seal.

The spark gap was placed in the center of the chamber. There is a large amount of excess wire in the chamber which would shorten the distance needed to create a DDT, but it apparently did not have any effect on the tests.

Upon ignition, this hybrid gives a small "squeak", which I assume is gas seeping past the ball valve seals. I was not close enough to tell for sure.

After ignition at higher mixes, the chamber was literally burning hot to the touch. I let it cool of for a couple minutes between tests.

So, in conclusion, I would encourage everyone to use this test as a baseline for judging the limits of their own hybrid. Remote firing is a still a must, as this hybrid is probably not the same as yours.

Edit: I just opened up the chamber today, and the entire inside is covered with some type of black goop. I have no idea what it is, as the only thing in that I got in the chamber before was a couple drops of pipe dope. This doesn't even smell like pipe dope. It's also gumming up the ball valve.
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Last edited by Fnord on Mon Sep 17, 2007 1:36 pm, edited 3 times in total.
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Unread postAuthor: frankrede » Sun Sep 16, 2007 12:30 pm

Interesting!
I'm glad someone did such tests, really makes me want to get my steel hybrid in working condition and recalculate the meter and shoot it.
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Unread postAuthor: iPaintball » Sun Sep 16, 2007 12:48 pm

THis was a very detailed test. I can't beleive you couldn't gey it to rupture!
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Unread postAuthor: c19o » Sun Sep 16, 2007 12:54 pm

So I guess its safe to hold a 500psi golfball launcher on CO2? Because I'm planning to make one , or a semi-automatic marble gun. What were the pressures you got at 11x 160psi?
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Unread postAuthor: Fnord » Sun Sep 16, 2007 1:04 pm

I can't say for sure, as I don't have a peak pressure gauge that goes that high. 2" threaded sch40 steel has an estimated burst pressure of ~1300 psi.
Someone needs to do some gaseq number punching.
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Unread postAuthor: jackssmirkingrevenge » Sun Sep 16, 2007 1:17 pm

It can probably take a lot more than that. 40mm grenade launcher rounds generate about 2600 psi and the barrels made for them are usually surprisingly thin walled. Of course metal quality varies, but I do feel folks on here sometimes overly cautious. Nothing wrong with that of course, safety first :)
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Unread postAuthor: SpudBlaster15 » Sun Sep 16, 2007 1:46 pm

Did someone say pure oxygen?
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Unread postAuthor: spanerman » Sun Sep 16, 2007 2:26 pm

and MAPP......at a 11x mix....and a peak pressure guage would be a great idea to give conclusive numbers about combustion pressures,,,
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Unread postAuthor: mopherman » Sun Sep 16, 2007 2:26 pm

jackssmirkingrevenge wrote:It can probably take a lot more than that. 40mm grenade launcher rounds generate about 2600 psi and the barrels made for them are usually surprisingly thin walled. Of course metal quality varies, but I do feel folks on here sometimes overly cautious. Nothing wrong with that of course, safety first :)

lol this is coming from the guy who took pvc to 400pi :lol:
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Unread postAuthor: DYI » Sun Sep 16, 2007 3:03 pm

Good job!

I was looking forward to seeing the results of this test, so its a shame that there really are none. Now I'll have to find out myself what it does take to break that stuff. How big was the spark gap, and what was the voltage of your ignition source?

Also, what did you do to protect yourself from the shrapnel which could have resulted from this test, and how far away were you when you were fueling it?
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Unread postAuthor: Fnord » Sun Sep 16, 2007 3:20 pm

the spark gap was .022" exactly.
Voltage was 35kv (my hybrids ignition).

At first I dug a post hole and put the hybrid in it during firing, but I had problems with the spark arcing though wires and into the ground. I ended up putting it behind a big stack of 4x4s and hiding behind a large air tank. At higher mixes I started throwing sheets of plywood on top of it just in case. I was about 30 feet away upon ignition, but I was right beside it when adding propane and air (I used a tank rather than a bicycle pump to avoid flash ignition).

On an unrelated note, how did this happen?

Edit: OOOH... now I see.. for whatever reason I read the first time as 14:47, not 14:17, so it looked like jack posted 1minute after SB15. I think I need to set my text size up :)

Sorry for the confusion.
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Last edited by Fnord on Sun Sep 16, 2007 5:31 pm, edited 1 time in total.
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Unread postAuthor: iPaintball » Sun Sep 16, 2007 3:27 pm

He just posted later...
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Unread postAuthor: Pete Zaria » Sun Sep 16, 2007 3:30 pm

@_Fnord,

Thank you VERY much for your contribution here! This is awesome data, and I think I can safely speak on behalf of the whole board when I say "GREAT JOB, THANK YOU VERY MUCH!".
If you get a chance to run a few tests again with a peak pressure gauge setup, that'd be awesome.

I think the time thing is just because you have your preferences set to display military (24-hour) time...

Peace,
Pete Zaria.
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Unread postAuthor: Fnord » Sun Sep 16, 2007 3:31 pm

He just posted later...


Then why wouldn't his post be down below? Am I missing something?

Pete: you are welcome :)
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Last edited by Fnord on Sun Sep 16, 2007 3:33 pm, edited 1 time in total.
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Unread postAuthor: VH_man » Sun Sep 16, 2007 3:31 pm

i would do the same for SCHD 80 PVC and see what happens....... i want a video though, i wanna see the KABOOOOMMM!!!
lol.

anyway, a peak pressure would be nice. i gues it tursn out i could make a CO2 chamber out of this stuff..........
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