Why would 2 out of 3 sprinkler zones cause the pressure reading at the pump to drop to 0? This is a well irrigation system and it is separate from the home's well. The pump is a 3/4 HP, has a flow rate of 10 GPM and is designed to maintain pressure at 40 PSI. The pressure tank is 2.1 gallons. The pump turns on at 30 PSI and off at 50 PSI. Zone 3 maintains 40 PSI perfectly, but zones 1 and 2 immediately drop to 0 PSI when activated, occasionally creeping up to 10 PSI but no more than that. There is still flow to the heads but they don't pop up. Is it possible there is a leak in both zones? If so, why would the symptoms be identical? Surely it would vary to some degree? I see no sign of leakage either, even after capping off all the heads. With capped heads, all symptoms are the same (0 PSI reading at the pump with an occasional 10 PSI). Assuming there is no leak, why would the pressure not build up with capped heads? If one zone is working fine, it couldn't be the pressure tank or pump, could it? The only thing I can think of is that there is a large obstruction in the mainline before the bad zones but after the good one, but even then, why would it not build pressure (since it's an obstruction)? The water must be going somewhere. Any help appreciated.
I ended up fixing this issue by capping off the heads and turning the system on for hours at a time as opposed to just a few minutes. This extended time running the system while capped off allowed buried line breaks to be revealed. There were multiple line breaks and crushed heads run over by vehicles in the past. I fixed all this last summer. As a preventative for future breaks I placed concrete doughnuts around each head.