Please clarrify HPA tank measurements.

[DougT]

It seems there are multiple ways of rating the capacity of a HPA tank.  Breating air minutes, cubic feet, cubic inches.  I'm looking at buying a 90/91 cubic inch 4500# carbon fiber paintball tank to use for filling my 850 while in the field.  

I'm guessing that the 44 cubic foot measurement is how much air at normal atmospheric pressure can be compressed into this tank.

I'm also guessing that the 91ci tank is the internal volume of the other tank.  

How do these relate to each other capacity-wise?

[kiwi]

the  volume rating is at the pressure rateing.....
Holds 44 cubic feet of air@ 3000psi or what the tanks rateing is...
 44  x 1 foot squire blocks would make a BIG pile way bigger than
a tank....

Pete

[DougT]

I just found the answer after a thorough internet search.  

A 68ci 4500# tank is equivalent to a 12 cubic foot tank.

A 91ci 4500# tank is equivalent to a 16.1 cubic foot tank.

Look at line #4 and substitute in the size and pressure.   http://www.gearseds.com/curriculum/images/figures/Pressure%20and%20Volume%20Worksheet.pdf

It looks like a 91ci 4500# tank will completely refill the Mrod 7 times and the 850 5 times at the pressures we intend to refill at.  Tanks, stainless on/off adapters, braided steel hoses, ect. parts on ebay for under $150 total.

Should make a nice weekend camping or day shooting setup.