calculate GPM

[gbutts]

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.

[valveman]

That pump will do 150 GPM at 54 PSI. Just to get the minimum run time of 1 minute you would need five 119 gallon bladder tanks. It would be better to have twice that many and get a two minute run time. About a 1,000 gallon standard air over water tank will work if you set up a good air charge system.

What you really need is a 3” Cycle Stop Valve to use with a single 80 gallon bladder tank. It will actually work better than a bunch of big pressure tanks.

[gbutts]

Valveman:

I had read elsewhere about the cycle stop valve - have not found a contractor in the area yet who is familiar, they keep trying to sell vfd. Guess I need to keep looking.

[Porky]

Yes, I suggest that you keep looking. A qualified pump installer will know about CSV's, if they don't look further because they aren't up to date with what's out there. Try it, I promise you'll like it.

[valveman]

The CSV is a “disruptive product”. It makes pumps last longer and use smaller pressure tanks. So it disrupts the industry by knocking everyone out of sales. If you have a CSV they don’t get to sell you a bunch of tanks, an expensive and short-lived VFD, and the pump will last many times longer. The VFD makes them more money because it is expensive, doesn’t last very long, and shortens the life of the pump as well. Only the most honest and reputable pump installers will even mention a CSV. And apparently, honest, reputable, and educated installers are becoming few and far between.