Help diagnosing low pressure

[ScottD]

Hi,

One of the zones in my backyard has low pressure. This zone has pop-ups, and all the rest have impact heads. The pressure in the popup zone is too low to fully push up the heads so the lawn never really gets watered.

Here's the strange part: If I unscrew one of the popup heads and let it run for a while (10-20 seconds) then the flow increases. You can actually hear it increase in the house (the sprinklers run off city water.) After that, I shut off the water, screw the head back on, turn the sprinklers back on and they work great. So the pressure is there, I guess the valve is not opening up all the way...? A friend suggested air bubbles might be the culprit.

Is there a test I can do to check and see if the solenoid valve needs cleaning/replacing without digging it up? Is there something else it could be?

[mike1059]

It sounds like the solenoid is not fully opening and needs to be replaced. I have seen this problem many times and a new solenoid will usually fix the problem. Once you find which valve in the valve box is the problem and get the proper solenoid you just turn the main water off, unthread the old solenoid and install the new one. That should cure the problem.

[ScottD]

Thanks for the reply. I think you're right... I started digging out the valves and the solenoid on the valve for that zone was wet. I unscrewed it and it seemed like a lot of dirt had gotten in the threads, preventing a good seal. I cleaned it out and screwed it back in, and it seemed to fix things, but then I checked again later in the day and it was still failing to open up fully. If I open the manual bleed valve everything works great, so it must be the solenoid.

I have no idea what the brand of the control valve and solenoid are, though. This system came with the house. I can't see any markings. The irrigation system could be 10-20 years old (some of the sprinklers have tall trees directly in front of them, which I'm guessing weren't there when the the system was installed.) I really don't want to replace the whole control valve. It's in a very awkward place.

The control valve is in-ground, screw in (not jar top) and white. The solenoid is black, cylindrical, with a silver-colored metal hexagonal-shaped plunger. Anyone know what brand it might be? I can post pictures if that helps.

[mike1059]

A photo would help but it sounds like it could be an old buckner or a slightly newer weathermatic. Eather way a universal solenoid from home depot or another source should fit the valve.