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Propane Meter PSI

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Propane Meter PSI

Unread postAuthor: frozenplum4 » Wed May 04, 2011 9:41 pm

I have built a propane meter and am wondering how much psi you use to fill your launcher. I figured it to be 3 psi in the propane meter, that seems really low to me.
I used the plans from mfanda.net (thanks for the great website). My chamber is 4" in diameter and 3 feet long.
Thanks for any help.


Edit by Moderator (MrCrowley): Please read the topic section description before posting in that section. You posted in the showcase section which clearly states is only for finished projects, a section for where you want to show off your cannon. You need to post in the discussion section which is for...discussing.
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Unread postAuthor: Crna Legija » Thu May 05, 2011 3:54 am

we need to know the volume of your meter pipe to help.
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Unread postAuthor: frozenplum4 » Thu May 05, 2011 8:00 pm

THe gun is around 500 cubic inches and the meter pipe is about 20 cubic inches.
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Unread postAuthor: mark.f » Thu May 05, 2011 8:41 pm

That meter pipe is HUGE... 4% of your chamber volume already, so fill to 15 PSI. I don't think you read the instructional close enough. :wink:

I see what you did. The equation I wrote for for PSIA, not PSIG, so subtract 14.7 from your answer to get gauge PSI.
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Unread postAuthor: frozenplum4 » Thu May 05, 2011 9:09 pm

Oh thanks, I didn't read the page close enough. I can't wait to get this thing going
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Unread postAuthor: frozenplum4 » Thu May 05, 2011 9:22 pm

What is a common volume for meter chamber? I think I did my math way wrong and when I redid it I got 1.1 cubic inches. Is that close?

Edit: The main chamber of the meter is 6" of 1/2 inch piping. I got a final psi of 290. Is that possible to get out of a propane tank?
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Unread postAuthor: Crna Legija » Thu May 05, 2011 10:37 pm

make is smaller and you fill it to around 35-40 psi. you could make it like 1 cubic and fill it to 20psi, i think not 100% sure on it.
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Unread postAuthor: mark.f » Thu May 05, 2011 11:26 pm

If you're gun is really 500 cubic inches, you need a much larger meter pipe.

Are you sure you did the math for your combustion chamber volume correctly? Even if your chamber was made from 4" SCH-40, it would have to be 40 inches long...
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Unread postAuthor: frozenplum4 » Fri May 06, 2011 5:51 pm

Yeah, It's 36" long and then there is a little less then a foot of 3". I just rounded up for convenience sake. How much bigger do you think it should be?
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Unread postAuthor: mark.f » Fri May 06, 2011 5:55 pm

I would move up a to 3/4" meter pipe about 18" long for a manageable meter pipe pressure (especially during cold weather). This would give you a meter pipe pressure of about 31 PSI.
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Unread postAuthor: frozenplum4 » Fri May 06, 2011 6:05 pm

Okay, thank you
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