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math help needed

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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math help needed

Unread postAuthor: Demon » Sun Mar 22, 2009 5:46 pm

I would need help for maths to know how much shot of 40 psi i could fill
a 1.5 inch per 8 inch chamber

http://74.125.95.132/search?q=cache:AET ... clnk&gl=ca

I am not shure to know how much is the propane bottle pressure but the link is up there.

The chamber is 15 c.i. and the propane bottle is approx: 40 c.i.

I would need 40 psi in my air chamber per shot.

How much shot could i get out of it?

Thank to reply.
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Unread postAuthor: Ragnarok » Sun Mar 22, 2009 6:01 pm

We need to know the mass of propane in the bottle - not the bottle volume - to be able to tell you this.

Sorry.
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Unread postAuthor: Lentamentalisk » Sun Mar 22, 2009 11:06 pm

he is using the propane tank as an air chamber, not a propane tank. I really don't want to do the math though.
PV=nRT is the equation you will be using though.
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Unread postAuthor: Ragnarok » Sun Mar 22, 2009 11:24 pm

Lentamentalisk wrote:he is using the propane tank as an air chamber, not a propane tank.

Well, in that case, we need to know the pressure he'll be filling it to.

Either way there is not enough information to answer the question.
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Unread postAuthor: Demon » Mon Mar 23, 2009 6:31 am

Wait, you mean that you need to know how much grams of propane there is in the bottle?

They say its 14 ounces.
he is using the propane tank as an air chamber, not a propane tank.


My air chamber is in pvc ( and it is connected to the sprinkler valve ).

The propane bottle is going to fill the air chamber (the pvc one) of compressed gaz, i am not using the propane tank as an air chamber but like a co2 catridge.

All what i know is that at the room temperature , the propane vapor pressure is 124 psi.
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Unread postAuthor: ralphd » Mon Mar 23, 2009 6:41 am

Here is a P/T chart for propane. That was in interesting article. I'd rather use a fire extinguisher or something with a little more volume. Newer refrigerant tanks have a built in check valve to prevent people from reusing them. It's too bad to, I can get these for free at work then put them on Ebay,

http://www.glacierbay.com/ptchartpropane.asp
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Last edited by ralphd on Mon Mar 23, 2009 3:59 pm, edited 1 time in total.

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Unread postAuthor: CpTn_lAw » Mon Mar 23, 2009 7:42 am

It is very simple :
Your chamber volume is Pi * squared radius * length in your case roughly 14 ci.

40 psi in your chamber means there will be 2,76 (40psi =2.76 bars) times the volume at atmoshperic pressure, means 14 * 2.76 = 38.64 => 39 ci of gaz

you have a lot of chance, this is almost the volume of your propane bottle.
means that to have 40 psi in your chamber, you need 40 ci of gaz from your bottle. The rest is self-deductive, one shot = 40ci of gaz.
If you know the mass of propane, then you know the volume it takes when in gazeous form, and you have your number of shots.
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Unread postAuthor: Ragnarok » Mon Mar 23, 2009 8:31 am

A 14 ounce propane bottle could fill a 15 ci chamber to 40 psi...

...uh huh, convert to metric*, carry the one, multiply by molar gas volume, divide into the other...
* Can't abide Imperial units for this kind of work. I barely use them myself any more, unless it's for an approximation of length or mass.

...about 300 times depending on exact conditions on that day, assuming I haven't made any mistakes.

Can't be much more precise than that, given the potential for variations in initial tank fill, exact temperature, etc, etc.
Expect that it could swing a couple of dozen either way from that estimate.
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Unread postAuthor: CpTn_lAw » Mon Mar 23, 2009 8:49 am

I'd say it's pretty much everything we can do for him...Thanks Rag for the propane thingy ;) I don't know anything about propane, and my last chemistry lessons were like three years ago...
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Unread postAuthor: Demon » Mon Mar 23, 2009 2:57 pm

300 times! that is a lot!

I expected 3 to 4 time .

so a co2 bottle would fill it like 2000 times
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Unread postAuthor: Ragnarok » Mon Mar 23, 2009 3:27 pm

Demon wrote:300 times! that is a lot!

It did seem like a big number to me when I did the maths, but I'm pretty sure it's right.

A 15 ci chamber at 40 psi is pretty small, so it can be filled a lot of times.

so a co2 bottle would fill it like 2000 times

Actually, there wouldn't be much difference for the same bottle size.
A CO2 bottle of the same nominal filling mass as a propane bottle will have the same cubic volume output, as Propane and CO2 have the same molecular mass.
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