Low pressure on one zone only

[flang1210]

One of the 5 zones of my sprinkler system has low water pressure. But when I manuely open the test screw on the valve controlling that zone, the water comes out normally. Any idea please? Thanks!

[tomm]

One of the 5 zones of my sprinkler system has low water pressure. But when I manuely open the test screw on the valve controlling that zone, the water comes out normally. Any idea please? Thanks!

solenoid..

[Wet_Boots]

It can also be a failing diaphragm assembly.

[flang1210]

Thanks guys. I think I found the reason. Somehow when I backed out the solenoid about a turn, the pressure came back on! Apparently the solenoid got screwed too close to the little relieve hole and preventing it from releasing full pressure. Can't explain how it got to be that way after several years working properly.

[tomm]

Thanks guys. I think I found the reason. Somehow when I backed out the solenoid about a turn, the pressure came back on! Apparently the solenoid got screwed too close to the little relieve hole and preventing it from releasing full pressure. Can't explain how it got to be that way after several years working properly.

Are you in freezing climate? What brand valve are you talking about?

Some solenoid/plunger assemblies retain water even if blown out/drained.
When the water freezes it distorts the solenoid/plunger.

[flang1210]

I'm in Houston, pretty warm most of the year. It is Orbit.