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New to hybrids

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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Re: New to hybrids

Unread postAuthor: Juggernaut12121 » Wed Jul 23, 2014 2:33 pm

I figured if the spark plug was opposite the fill port then it should get a decent mix of fuel and air, although I'm not too sure is it will take a nother effect and just become a pocket of air or something.
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Re: New to hybrids

Unread postAuthor: noname » Thu Jul 24, 2014 3:27 am

There's nothing wrong with that line of thought - it should work just fine. I could never get it to work personally though. :wink:

That being said, my lack of tools hinders every one of my projects and could contribute to an ignition failure somewhere in there.
Try out the ignition setup for yourself. If it works, great. If not, oh well. You're working with threaded metal parts so it's relatively easy to disassemble reconfigure your parts.
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Re: New to hybrids

Unread postAuthor: Juggernaut12121 » Thu Jul 24, 2014 6:39 am

Thanks for the input, once I get enough money I'll start to build it :D

Update: I can't find any reasonably priced npt spark plugs online, if I don't find one in my stores then I'll make my own with a hose barb or something
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Re: New to hybrids

Unread postAuthor: D_Hall » Sat Jul 26, 2014 6:05 pm

~NooooooB~ wrote:Do you know where I can find any that have NPT threads? I've found a few online but they're all pretty expensive,

Never even bothered to look. Instead I bought a tap to thread any damned hole I want to match the model of spark plug I picked.

that and should I insulate it with a pvc bushing or is that unsafe

No need to insulate. That's what makes spark plugs great... They're literally made for this.

And one lat question if you're willing, I thought using a tee in the middle of the chamber, then off of that tee I'd put another tee, one branch going off to a ball valve and fill port and the other to the spark plug. Would this actually be a viable ignition setup or would it create some sort of pocket creating trouble?


Not sure why you'd go that route, but it should be OK.
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Re: New to hybrids

Unread postAuthor: Juggernaut12121 » Sat Jul 26, 2014 6:22 pm

I don't have any way of making a proper hole in the chamber and threading it, that and I figured that drilling a hole in the chamber would create an unnecessary weak spot
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Re: New to hybrids

Unread postAuthor: MrCrowley » Sat Jul 26, 2014 6:25 pm

Use metal fittings and just epoxy the sparkplug in one. I use a 25mm x 15mm threaded bushing, push the spark plug up through the bottom and epoxy it in place. The wide hexagonal body of the spark plug can't fit through the 15mm female threaded hole so there's almost no possibility of the spark plug being blown out of the fitting.
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Re: New to hybrids

Unread postAuthor: D_Hall » Sun Jul 27, 2014 10:36 am

~NooooooB~ wrote:I don't have any way of making a proper hole in the chamber and threading it, that and I figured that drilling a hole in the chamber would create an unnecessary weak spot


A quick/easy method is to buy a pipe plug and drill into it. True, all you're doing is creating a bushing that adapts your spark plug to NPT but it's a classy way to do it that only costs a couple bucks.

A tougher way is to drill through a boss for your spark plug, drill through your chamber to match the boss, and then weld the boss in place. Even cheaper from a dollars perspective, but obviously assumes more skills and equipment available.
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Re: New to hybrids

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Re: New to hybrids

Unread postAuthor: Juggernaut12121 » Thu Jul 31, 2014 12:34 pm

I might try epoxying a spark plug into a bushing; just to be positive, you would just attach the other lead of the ignition circuit to the body of the gun right?
And I seem to be full of questions :P, would I be alright using a regular ball valve on the gun or should I try to find a high pressure one? And for my fueling setup (it should only need to take about 150 PSI) would I be alright using regular brass quick connects?
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Re: New to hybrids

Unread postAuthor: SpudBlaster15 » Thu Jul 31, 2014 1:22 pm

For chamber isolation, I would definitely go with something more robust than a standard 600WOG ball valve. I experienced several failures at higher mixes, using atmospheric air with and without additional oxygen. A 3KPSI hydraulic BV should work well. Brass quick connects will also be fine at 150PSI.
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Re: New to hybrids

Unread postAuthor: Juggernaut12121 » Thu Jul 31, 2014 3:48 pm

Thanks! I hate to ask so much but does anyone know where I can find them for a reasonable price? I found a few but they where several hundred USD a piece :/
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Re: New to hybrids

Unread postAuthor: D_Hall » Thu Jul 31, 2014 9:54 pm

Don't forget that for fueling you don't need a large valve. Smaller is better. It'll be cheaper, provide increased injection speeds (better mixing), and will be rated to higher pressures (given similar construction techniques). A quick check of mcmaster gives me a 1/8" valve rated for 7000 psi for $37.

http://www.mcmaster.com/#4715k11/=t3180z

Took me about 2 minutes to find that and mcmaster is *always* over priced. Look around a bit....

Oh, and you should only need one. You're just trying to isolate your fueling system from your combustion chamber. Use a manifold and you can use normal (cheap) components for the rest of the fueling system.

edit: A bit cheaper ($35) would be a 3000 psi check valve. Again, just something to protect your fueling system... http://www.mcmaster.com/#5843t41/=t31b80
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Re: New to hybrids

Unread postAuthor: Juggernaut12121 » Fri Aug 01, 2014 6:10 am

Thanks, I'll have to look around a bit , I forgot about check valves
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Re: New to hybrids

Unread postAuthor: noname » Fri Aug 01, 2014 1:24 pm

I've always liked SB15's method of filling air directly through the fueling manifold. It allows you to only have one valve to shut off the combustion chamber from all the gauges, filling, etc. It also ensure proper mixing, which I had trouble with previously.
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Re: New to hybrids

Unread postAuthor: Juggernaut12121 » Fri Aug 01, 2014 1:46 pm

I was planning on making a manifold for both fueling and pressurizing, if that's what you mean?
I just wasn't expecting to pay so much for safe ball valves :P
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Re: New to hybrids

Unread postAuthor: noname » Fri Aug 01, 2014 3:12 pm

Yep, a fueling/filling manifold is what I was suggesting.
I've only ever used a ball valve rated to 600 psi, just an ordinary ball valve off the shelf at the hardware store. It's always worked fine, but I've only shot at 6x mixes with it. I trust it would hold up to much higher mixes though.
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