I hope some one can help me -- I am getting conflicting opinions on the size of pressure tank required for my irrigation system. It is an old system that looks like it was put together out of spare parts, the existing pressure tank is in excess of 50 years and has now sprung leaks everywhere. Contractors who have looked at it all agree it is to large but disagree widely about what size is required. System provides water to 100 some hose bibs spread out over the 100 acre property. I draw water out of a pond - pump is a Berkley with 6" impeller model number looks to be B-1 1/2 TPMS, hard to read as it has been there a while. It is powered by a 7.5hp 208 3 phase motor with 3400 RPM. It draws from the pond out of a 4" line, pipe into and out of pump head is 1 1/2" and the increases to 4" into the tank with a 4" main line going out to the site. Any input you may have as to proper tank size is appreciated.