Question
I have a 1HP Gould shallow well pump with a pressure tank that has a static pressure of 45 PSI (verified with another gauge on a separate faucet). I think it's an old irrigation system (was here upon moving in 2 yrs ago), with mostly Toro rotors (Super 600, not made anymore) and 570 sprayers, some Rainbirds mixed in, about 35 heads in 5 zones.  Two zones no longer have enough pressure to come on all the way unless they are started individually (not in succession after another zone).   The gauge on the well pump reads between 34 and 39 (depending on the zone) when the zones are activated and working okay, but anything below 33 and the zone won抰 get going.  

I tried to calculate the total GPM for just the heads in each zone (with what specs I could find) and all but one zone came out around 12-14 GPM, but that was assuming 30 PSI.  I measured the pressure at one of the heads in two separate zones (I did this at a 1 foot above-ground riser because it was easily accessible for the screw-on gauge), and recorded a PSI of 20 and 19 PSI, both Super 600 rotors.  

I know the system is not getting enough pressure, and it seems to have gotten a little worse in the last two years (although I think the prior owners had some trouble with pressure as well and mentioned to not use a hose at the same time as the sprinkler system).     

I realize you probably need more information, but do you think this is a well pump problem, and could it be remedied by getting a pump with more HP, or just a new well-pump?  I had the well folks out last year, and they did replace a part of the pump, but it didn抰 make a great deal of difference.  I think the water supply is okay (but not certain)厀e live in north FL, and I want to avoid the expense of drilling, if possible.

Or could this be a system problem?  I think the system must be very old, and may have been homebuilt.  I抳e dismantled and cleaned some of the heads, with a very slight improvement.  I抳e been thinking of replacing some of the heads with lower flow ones (and just watering longer) if that guarantees the zone will at least come on all the way.  Is that pressure loss normal?  Anyway, thank you for whatever help you can provide!
Robert
Jacksonville, FL


Answer
Sounds like you need a new pump. The pressure at the farthest head should be 30lbs for a spray and 35lbs for a rotor. Those pressures are what you need to run those heads effectively. A 1hp pump should do the trick especially if you you have a tank with it. Make sure your tank is working properly. 12-14 gpm on a 1hp pump is nothing that's why I say check the pump. If you have anymore questions please write back.