Hydropheumatic tank sizing

[ncsuboy]

NC admin code give an example of sizing a hydro tank as peak demand - pumping capacity x 20 min = required effective volume
so if i have (60-30)x20=600 gallons
then they state the total volume if you use a 60-40psi pressure cycle with automatic air water volume controls is required effective volume/0.25. So 2400 gallons
I assume this is based on Boyle's Law. What affect and how do you calculate the volume with precharging? How does this work. With no control the percentage of water would be 7% of the total volume on a 60-40 pressure cycle. so 8570 gallons in my example. Big difference. School me please.

 

[cvg]

try the attached document which may help in your design

 

[ncsuboy]

Very usefull, thanks for the information.