Efficiency test math? So, I did an efficiency test with my Valken Proton but I had 2148 (2009 after airing up) PSI in a 50ci tank. I'm trying to figure out how my math is and where I'd need to go in order to get a PSI/in3 at 4000 PSI and then the PSI per shot. So far, I've got a basic equation for PSI per cubic inch which would be 4000/50= 80PSI per cubic inch. Is this correct? If so, at 576 shots (I counted the paintballs before I did the test and had each pod labeled) off of a ~2000 fill doubled to reflect 1152 shots off of a ~4000 fill, would it be 1152/50=23.04 shots per cubic inch? Finally, if both of those are correct, would it be safe to assume that it's roughly 80psi for 23.04 shots off of one cubic inch at 4000 PSI that could then be multiplied by the size in cubic inches of a tank? Meaning a 68/45 would be roughly 1550 shots per 68/45 filled to 4000 PSI? 
I don't have my fluids book on me but my lizard brain screams there has to be more to it than that. Let me do some digging. 
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the slash between 4500psi and 30in^3 is not a division. it's just a separator. it has no mathematical meaning. in fact i don't even know what you're trying to find out... 
Easiest way to approximate is with energy conservation. A 50/4500 has 225,000 inchpounds of potential energy (pressure times volume) when filled to 4,500 psi. The same tank filled to 2009psi has 100,450 inchpounds of potential energy. For example (not using your numbers)  If after 10 shots your tank pressure drops from 2,009 to 1,979 psi, then you have consumed 1,500 inchpounds of energy (100,450 inchpounds minus [1,979 psi x 50 cubic inches]), or 150 inchpounds per shot. Take the 225,000 of the full tank (inchpounds of potential pneumatic energy), divide by the energy per shot (150), and you get the approximate number of shots per tank. Actual numbers will be slightly different due to some conversion of energy to heat and simplification of the process as described above  but the numbers will be quite close. You can then compare your numbers to those of different size and pressure tanks just by dividing potential energy of the tank (pressure times volume) by the consumed energy per shot. 
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the second part is a reasonable assumption. its not strictly linear so you will likely find that you will get an even higher shot count on a full tank. You can't use the tank all the way down to 0 psi, but you can definately use it all the way up to 4000 psi. IE below 400 psi your gun won't fire so you only get to use 1600 psi off the bottom of the fill ( guesstimate numbers). for the top of the fill you get to use the full 2000 psi. 
Boy I'm glad the knowledgeable ones posted before I made a fool of myself. But to further clarify what Heinous was saying, a 4000 psi tank with 50 square inches of volume means that each of the 50 square inches is pressurized to 4000 (Pounds per Square Inch) 
Yeah... I have no idea why I was even thinking of pressure force per square inch. Basically, all I need are shots per 4k PSI. If it's 576 shots off of 2009 PSI (Rouding to 2000 to make life simple) would I just be able to multiply the amount of shots by 2 since I'm multiplying the pressure by 2, making it 1152 shots off of 4018 PSI (Rounding to 4000) then divide the shots by the tank volume in cubic inches, in this case, 1152/50=23.04 shots per cubic inch then multiplying by tank size? Example 576 shots2000psi * 2 = 1152 shots4000psi 1152 shots / 50 inches ^3 = 23.04 shots per in^3 23.04 shots per cubic inch * 68 ci = 1566 (rounded down) shots per 68 cubic inch tank at 4000 PSI I'm not trying to figure out the PSI per cubic inch, I'm trying to figure out the amount of shots per square inch in a universal factor if I possibly can. The only way I've come close to the system I'm using is because my in theory results are very close to those of a 68 cubic inch tank, a 50 cubic inch tank, and a 48 cubic inch tank. Would this solution work universally? 
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the unit you would be looking for is probably joules per shot. not very practical since it's a scientific unit and tanks are not labeled in metric, so every time you have another tank you would have to pick your brains out. 
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Fractionally comparing one tank size to another is fine. If you have shots per tank from a 50 cubic inch, you could expect 68/50 of those shots from a 68 cubic incher provided it is the same pressure. 
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