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number of shots from propane.

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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number of shots from propane.

Unread postAuthor: c11man » Mon Jun 22, 2009 12:12 am

i am going to be using propane as a altunative gas source when my aircompressor is unavalible for this gun
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it has a 15 cubic inch chamber and i would filling it to max psi (150psi because summer temps allow for it)

does anyone know the equation for finding the number of shots i can get from one disposible propane clyender or is nice enough to do it for me?

thanks
c11man
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Re: number of shots from propane.

Unread postAuthor: Technician1002 » Mon Jun 22, 2009 1:03 am

c11man wrote:i am going to be using propane as a altunative gas source when my aircompressor is unavalible for this gun
Image

it has a 15 cubic inch chamber and i would filling it to max psi (150psi because summer temps allow for it)

does anyone know the equation for finding the number of shots i can get from one disposible propane clyender or is nice enough to do it for me?

thanks
c11man


I've been thinking along the same lines for some t shirt launching. I don't have answers yet, but the thought process I am using is we know the weight of propane and we know the pressure and volume of the chamber. What we don't know is the mass of propane used per shot. If we attack it at that angle, the rest should not be too hard.

A good place to start is here.
http://answers.yahoo.com/question/index ... 726AATG7BI

Once we know the mass at STP, we can scale for the pressure used. For rapid fire, allow for lower temperature.

EDIT; Just found this;
Liquid density (1.013 bar at boiling point) : 582 kg/m3
Liquid/gas equivalent (1.013 bar and 15 °C (59 °F)) : 311 vol/vol


From here;
http://encyclopedia.airliquide.com/Encyclopedia.asp?GasID=53

Scale volume by the bar increase and you are done. Volume of liquid propane can be found by looking at tank volumes and the ratio in comparison to water weight is easy to find.

http://wiki.answers.com/Q/Capacity_of_Propane_tank_with_gross_water_capacity_of_285_gals
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Unread postAuthor: jimmy101 » Mon Jun 22, 2009 12:58 pm

The typical Bernzomatic propane cylinder (blue) contains 400 grams of propane.
http://www.hardwarestore.com/pop-print/ ... rodNo=7148

At STP (32F, 14.5 PSIA) that would be (molecular weight of propane is 44);
(400g)(mol/44g)(22.4L/mol) = 203.6L

Propane at 150 PSIG (165 PSIA, assumes a pretty hot day) ignoring other temperature affects;
P1V1=P2V2
(14.5 PSIA)(203.6L) = (165 PSIA)(xL)
x = 17.9L
So, that 400g of propane in the cylinder is equivalent to 17.9L at 165 PSIA.

Your chamber is 15ci chamber (0.246L), so shots per propane cylinder;
(17.9L)(1 shot/0.246L) = 73 shots

YMMV and there is always the possiblity I screwed up the math :D
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Unread postAuthor: c11man » Mon Jun 22, 2009 4:13 pm

thanks alot jimmy and tech.

73 shots seems a little low for how small my chamber is in my opion. but i could be wrong.

the number of shot will increase or decrease proporionaly with my chamber volume if i change it right?
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Unread postAuthor: Technician1002 » Mon Jun 22, 2009 7:19 pm

c11man wrote:thanks alot jimmy and tech.

73 shots seems a little low for how small my chamber is in my opion. but i could be wrong.

the number of shot will increase or decrease proporionaly with my chamber volume if i change it right?


Correct, except it's inversely proportional. Bigger chamber/less shots.

I haven't found any blatant errors in the math. As a double check I'll play with the numbers on volume alone using this from an earlier link above.

Liquid/gas equivalent (1.013 bar and 15 °C (59 °F)) : 311 vol/vol


A double check using the mole calculation and comparing it to the liquid to gas ratio will provide a fairly quick double check of the figures.

A 1Lb bottle of propane has the water capacity of 2.39 lbs of water.

1 lb of water is 27.680 cubic inches.
2.39 Pounds of water = 66.156 Cubic inches
66.156 Cubic inches of liquid propane = 20,574 cubic inches of vapor at standard pressure. Convert to your desired pressure to find the volume at the new pressure.
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Propane weight vs water weight for same volume.
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