SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

No practical experience here that I can use to help you with this exact situation, but here's a couple of logical thoughts and questions.

#1. Sounds like you already know the issue regarding various times of the day. However you can prove the issue there is with your water supply and nothing with your system by getting a water pressure guage. Assuming we're talking city water feeding both the house and irrigation, place the guage on a hose bibb that is before any pressure regulator for your home. Turn on the hose bibb and then run the system. Check the pressure at the hose bibb while the system runs. Try this at different times of the day to insure the city water pressure is fluxuating. That is most likely the case, but it's not outside the relm of posibility that something like temperature changes during the day are effecting some part of the system. Of course the other thing to pay attention to is water use in the house at the time the system is running.

#2. When you are automatically running the system, are you running only one zone at a time? Most controllers only allow one zone at a time, but if you have two controllers (or one that is powerful enough to run two at once) then I could see the posibility that in "auto" mode you are running two zones (and hence hurting your own pressure) compared to manually when you are only turning one on at a time.

#3. Do the vavles have a flow-control screw on them. If so, make sure the flow-control is set to wide open.

#4. Is it possible that sand or other trash has gotten into the valves? I could see a situation where sand is lodged under the selinoid and in "auto" mode, the selinoid isn't moving out of the way enough to allow enough water through the pilot hole, but when you try it manually, you create a larger gap and more water can get to the pilot hole. My gut instinct says this isn't the issue. This is just a pilot hole that once enough water is flowwing through the pilot hole, the main valve should open and the same amount of water should be able to flow through the main valve regardless of the amount of water flowing through the pilot hole. But I guess it's not impossible that this sort of partial blockage is such that it's like the valve is starting to try to close. Now I must admit, I don't totally know what I'm talking about here, and I would think it would take just the right conditions for this to affect the valve. But since you've got two valves with the same problem, it would be unlikely the same set of just-right conditions would be occuring in both valves.

If none of this is getting if for you, I have a feeling you're going to be digging SOMETHING up to replace (possibly starting with the valves).

The only other advice I can offer at this point (and it's pretty much too late if you don't want to be digging stuff up) but what sort of calculations did you do to design the system (such as how many heads to place in each zone). If you can begin providing some information here, I can try to help you determine if things are sized correctly. You would have to start with information such as what is the static water pressure of your city water, what size water meter do you have, what size pipe runs from the meter to the irrigation manifold and what is it's total pipe length. What sort of backflow preventer are you running (or is it anti-sipon valves). What sort of heads are you using, what is their individual flow patterns (full circle, half circle, quarter circle, etc), for each zone in question what is the average pipe length from valve to head. And that's just for starters.