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Propane questions...

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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Propane questions...

Unread postAuthor: saefroch » Fri Apr 23, 2010 10:04 am

I recently (a few days ago) started working on my pneumatic (soon-to-be-hybrid), and modded it so that it is no longer seals directly onto the barrel but uses a very long piston that seals against a bushing on the barrel side, and into a nipple on the back end (using an adapter as stop). When the piston slides forward, the back end is only out of the nipple by maybe 1/4". Pilot valve opens, piston slides back flawlessly. Right now, it's just a pneumatic, but I yesterday assembled a mechanism to meter and inject propane into the chamber. I have a few questions regarding the feasibility of the build now... probably should have asked these earlier, but oh well, I can mod it if I need to.

Question one: Does anyone know of an easy high-pressure tolerance method to inject propane into a chamber (through a shcrader is preferred- I already looked around on the hybrid section, not sure if any of the ideas will deal with high pressures well)?

Question two: What is the internal pressure of a propane tank (I know it is stored as a liquid so it will stay fairly constant through use)?

Question three: Advantages/disadvantages to Propane vs MAPP?
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Last edited by saefroch on Fri Apr 23, 2010 10:09 pm, edited 1 time in total.
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Unread postAuthor: Crna Legija » Fri Apr 23, 2010 10:10 am

lol just found this out 2min ago its about 120psi or 8 bar
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Unread postAuthor: Gaderelguitarist » Fri Apr 23, 2010 10:25 am

Are you converting it into a combustion or a hybrid?

1. If you're making a combustion, you can easily inject the propane via a metering device. If this is going to be a hybrid, you can take the same approach, but will then pressurize with air afterwards. either connect the metering device to the chamber with a threaded elbow, or thread on a female quick disconnect. The FQD has a seal preventing back flow.

*Question two has been answered*

3. Mapp gas burns faster than propane.
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Unread postAuthor: saefroch » Fri Apr 23, 2010 1:17 pm

Converting pneumatic to hybrid. Guess it's time to search the Combustion forum for metering devices...

As always, thanks very much.
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Unread postAuthor: MrCrowley » Fri Apr 23, 2010 5:12 pm

modded it so that it is no longer a barrel-sealing design, but it uses a very long piston that seals against a bushing on the barrel side, and into a nipple on the back end (using an adapter as stop). When the piston slides forward, the back end is only out of the nipple by maybe 1/4". Pilot valve opens, piston slides back flawlessly.

If it seals against the barrel, it is a barrel-sealing design :P
I don't understand what's different between your piston and any other coaxial cannon piston, it is a coaxial cannon piston, right?
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Unread postAuthor: saefroch » Fri Apr 23, 2010 9:48 pm

Not a coax, it's a tee piston. Seals against a bushing that the barrel screws into, so it can still actually fire a jet of air without a barrel, so not a true barrel-sealer, in that the front of the piston ends up slightly past the front of the tee in the sealed position.

EDIT: And I checked today actually, I'm pretty darn sure I was incorrect earlier, the piston is not exiting the nipple. The neoprene is just flexing to allow airflow around it, as originally intended.
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Unread postAuthor: MrCrowley » Fri Apr 23, 2010 10:01 pm

Not a coax, it's a tee piston. Seals against a bushing that the barrel screws into, so it can still actually fire a jet of air without a barrel, so not a true barrel-sealer, in that the front of the piston ends up slightly past the front of the tee in the sealed position.

You will find that very few cannons with tee pistons actually seal againt the barrel. Since most people want interchangable barrels, they do similar things to what you have done so they can swap out the barrel.
Though it is still called a barrel-sealer because you are sealing of the barrel port, not the chamber port as in a chamber sealing valve.
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Last edited by MrCrowley on Fri Apr 23, 2010 10:09 pm, edited 1 time in total.
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Unread postAuthor: saefroch » Fri Apr 23, 2010 10:09 pm

Terminology corrected. Thank you very much for reminding me that I am still new to this and heading off much more confusion.
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Unread postAuthor: jimmy101 » Sat Apr 24, 2010 12:16 am

The wiki is your friend.

http://www.spudfiles.com/spud_wiki/index.php?title=Propane

Image

The pressure in the tank will stay constant during a shooting session (as long as you are using the propane as fuel and not compressed gas). But the tank pressure will change by a fair amount depending on how hot the day is.
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Unread postAuthor: saefroch » Sat Apr 24, 2010 11:24 am

oooooooooooooooo thanks. I've been wondering where I could find a good phase diagram for things like nitrogen, oxygen, carbon IV oxide, and propane.
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