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Hybrid Safety Question

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 Safety Question

Unread postAuthor: Rob748 » Sat Jan 02, 2010 2:05 pm

Hi, I want to make a hybrid cannon, but out of PVC, Ive heard of the danger of ing polyvinlychloride, But I was pre planning, a 2inch schedule 80 or even 120. I looked at the pressure rating of a Schedule 80 2 inch chamber, and its rated clear up to 420, yet the 2.5inch chedule 80 is 470 ? kinda weird huh ?, but anyways Im not looking for a high mix, At tops 3x, I ran some numbers through HGDT, and at 2x with a 12 inch chamber the Maximum possible PSI is 220. I havent looked up the 120 schedule rating but I bet its close to 600 PSI. I know ovc has fatiqure problems and all but do you think Schedule 120 could handle up to a 3x mix with a spark strip and a chamber fan ?

Thanks
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Unread postAuthor: Moonbogg » Sat Jan 02, 2010 2:25 pm

It sounds like you are hell bent on using PVC, but have you considered aluminum pipe?
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Unread postAuthor: starman » Sat Jan 02, 2010 2:46 pm

I'll give a tentative safety OK to sched 80 or 120 at 3x hybrid mixes as long as all joints, endcaps, barrels, etc are also similarly rated. The chamber fan is much less likely to survive than in a standard 1x advanced combustion.

DO NOT fool around with a hybrid mix in a 12" PVC chamber...don't do it!!! Also don't go any higher than 3X with your other configuration.

Hybrid mixes are a whole different ballgame from air pressure (1x) mixes. You would be well advised to skip PVC altogether and go with all metal construction.
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Unread postAuthor: Moonbogg » Sat Jan 02, 2010 3:06 pm

Yeah its weird because the pressure rating of the PVC can easily handle the low hybrid mix, yet they have failed anyway. And of course when PVC fails its always explosively. I'd like to note however that my chamber fan in my large hybrid has held up great to constant 2x use and even a couple 3x shots. When I used pure O2 and mapp, thats when the fans bit the dust every time.
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Unread postAuthor: MrCrowley » Sat Jan 02, 2010 3:50 pm

Personally I wouldn't feel safe with PVC, maybe it's because i've built my own hybrid out of metal and it really scares the sh|t out of me sometimes.

I think it's better to go with some pressure rated ABS if you can find some. It can take shock and heat (or lack of) far better than PVC can and it doesn't fail so dramatically.

If this is going to be remote fired, go for it I say.
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Unread postAuthor: Heimo » Sun Jan 03, 2010 1:37 pm

Moonbogg wrote: When I used pure O2 and mapp, thats when the fans bit the dust every time.


I am fairly sure a metal fan would survive like this one I made a couple of days ago

Image

it still ain't perfect so I am going to remake this fan I am still developing my metalworking skills practice makes prefect

MrCrowley wrote:Personally I wouldn't feel safe with PVC


my personal philosophy with any launcher is: metal all the way
I cannot understand that people trust plastic so much.
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Unread postAuthor: jackssmirkingrevenge » Sun Jan 03, 2010 1:40 pm

Heimo wrote:I am fairly sure a metal fan would survive like this one I made a couple of days ago


Looks good, did you use an existing fan as a mould and cast it?
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Unread postAuthor: psycix » Sun Jan 03, 2010 1:47 pm

Yeah nice fan.
You should make a howto.
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Unread postAuthor: ramses » Sun Jan 03, 2010 1:53 pm

Nice work! I would make sure you had some kind of enclosure like a standard computer fan to make mounting easier.
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Unread postAuthor: Heimo » Sun Jan 03, 2010 2:04 pm

jackssmirkingrevenge wrote:
Heimo wrote:I am fairly sure a metal fan would survive like this one I made a couple of days ago


Looks good, did you use an existing fan as a mould and cast it?


correct

thanks for the kind works people

If there is enough interest I will make a how to in the off topic section

and maybe someday I will cover ammo molds when I have a need to make one
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