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C chamber material, spark gaps and misc. help needed

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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C chamber material, spark gaps and misc. help needed

Unread postAuthor: BigBang J » Fri Jul 09, 2010 2:39 pm

I think I am going to scrap pretty much my whole gun that I have been working on. The combustion chamber was made of 1/8" thick bronze tubing 4" long and 1" id. with brass washers brazed onto each end for caps and 1/4" and 1/8" female npt fittings brazed on the end caps inside the chamber.

I am now thinking of making the combustion chamber out of stainless steel. How well does 304 stainless steel drill & machine?

I am thinking of a tube with solid plugs fitted inside the ends of the chamber and bolted from the outside of the chamber.

How about spark gaps. I have not seen to much about that here, maybe I just did not look in the right place?

Obviously you want the hole to be pretty small so as to reduce surface area that pressure will be pushing against. But what kind of material should be used here?

Before I was using a ptfe tube threaded inside and out. this threaded into my chamber wall and a bolt threaded into the inside for the hot wire to connect to. I was using stun gun internals but the voltage I picked was to high and it eventually broke down the electrical resistance of the ptfe.
What is a good voltage to use? 50,000 volts enough?

Any thought here will be appreciated.
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Unread postAuthor: jakethebeast » Fri Jul 09, 2010 4:53 pm

i think 50,000 is enought, i suggest making a spark strip from acrylic material to have mayby 3 sparks?
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Unread postAuthor: mobile chernobyl » Fri Jul 09, 2010 5:51 pm

Not to be a shameless self promoter, but my hybrid is currently made out of 304SS, and features a coaxial multi-spark strip design.

I might be rebuilding just the chamber out of sch40 steel tubing, for "future-proofing" if you will :wink:

Here's the thread on it sofar...
http://www.spudfiles.com/forums/10x-hyb ... 21142.html

Hopefully it can be of some help to you. :idea:

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Last edited by mobile chernobyl on Sat Jul 10, 2010 7:02 pm, edited 1 time in total.
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Unread postAuthor: BigBang J » Fri Jul 09, 2010 8:30 pm

Yes but how about where the spark "plug" enters the combustion chamber, what is the best way to do that and still be able to withstand a ton of pressure and heat? I don't want to take any shortcuts, I kinda started to on my first hybrid.

Ahhh, yes I have viewed that one a few times already. Why are you rebuilding the chamber from steel? Whats wrong with the old chamber?
aha! so the spark strip enters the rear of your launcher?
How is it holding up? have you pulled it out after some time to see how it is?
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Unread postAuthor: Crna Legija » Fri Jul 09, 2010 9:53 pm

Is this a combustion or hybrid?
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Unread postAuthor: mobile chernobyl » Sat Jul 10, 2010 7:04 pm

BigBang J wrote:Ahhh, yes I have viewed that one a few times already. Why are you rebuilding the chamber from steel? Whats wrong with the old chamber?
aha! so the spark strip enters the rear of your launcher?
How is it holding up? have you pulled it out after some time to see how it is?


I haven't gotten a chance to test the spark strip during a combustion yet, but I really have no doubts it will hold up. If you need any more info on it, let me know and I can send you a more detailed view and explanation on it, but shoot me a private message if you want that.

I nixed the chamber renovation idea. I simply fixed the union direction and re-welded it back together - I'm sticking with 10-12X for this hybrid, and I'll keep higher mixes the plan for next year with a completely new hybrid gun.
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Unread postAuthor: BigBang J » Sat Jul 10, 2010 7:16 pm

-_- wrote:Is this a combustion or hybrid?


This is a hybrid, I am looking to have a pressure of 1000 psi after combustion.
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