I have a property in a forest area with a 1/2 acre orchard and some surrounding areas requiring irrigation. I currently irrigate by pumping water from a large stream. I am looking into installing one or two large water tanks (perhaps as much as 15,000 gallons) on a hill which is a little over 100 feet above the areas needing irrigation. I also plan to connect the tanks to a sprinkler system which can operate as a "turn it on and run" system to wet down the area as much as possible in the event of a fire.

So as I understand it, tanks at 100+ feet gives me about 40 psi at the area where I will have my valves. From there to my heads it will be fairly flat. I believe that how many heads I can have on a single line depends upon the pipe diameter - greater pipe diameter = greater flow, right? I am using simple impact sprinklers which give specs as roughly 4 GPM at 40 psi. I'm having trouble finding the math on this, that is, flow at 40 psi for pipe diameter X is Y GPM; or: "if you run 1" pipe from a valve on a 150 ft line you could run X number of sprinkler heads on that line"; "if you run 1-1/2 inch pipe from a valve on a 150 foot line you have less friction, greater flow and you could have Y number of sprinkler heads on that line."

Okay, if I'm making any sense, and someone knows a layman's source for such calculations (please, no references to Reynold's number calculations!), please let me know. I know irrigation hydraulics can get fairly complicated, but I'm hoping the calculations on my system can be fairly simple.