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Thursday, March 13th 2008, 3:42pm

Control valve has higher pressure when turned on manually

Hi everyone,
First post on this forum. I'm a forum junkie, so I love to use them for information.

I just redid my front lawn about two weeks ago. I had the old St. Augustine lawn hauled out by someone else, but I rototilled, laid sprinklers and laid the Marathon II sod myself. It turned out great!

I did alot of reasearch, but made a few rookie mistakes. One was putting the sprinkler heads a little bit too far apart (probably due to not anticipating the pressure loss over distance), or using 1/2" pvc pipe rather than 3/4". But, I used alot of heads (two zones in my 1250 sq. ft. lawn), and the lawn is very green and wet after watering, so it seems to be working well.

Here's my issue. When I installed the sprinklers, I tested them by turning on the control valve manually, since I hadn't wired it up to the controller yet. It works great, and my 3" pop ups work very well. But, when the controller turns on the sprinklers, they have less pressure. It is pretty dramatic, and I'm not at a point where I want to dig anything up and redo it.

One of my control valves is older (was in before I redid the lawn), one is brand new for the second zone. Both experience the exact same issue. I believe that the controllers are 3/4", and I used 1/2" pipes to the sprinklers. (I wish I had used 3/4" or bigger, but live and learn) :(

The pressure also seems to be very different depending on the time of day, which I assume is due to more demand due to neighbor use of the shared water supply.

What would cause the sprinklers to be more powerful when turned on manually? Is there anything I can do, as far as any modifications to the insides?

Thanks for any information.

This post has been edited 1 times, last edit by "jcm3" (Mar 13th 2008, 3:58pm)


Supreme Member


Friday, March 14th 2008, 1:22pm

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.


New Member


Wednesday, March 19th 2008, 3:13pm

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)

Good call. I was mistaken about both valves experiencing the same thing. I double-checked them after I posted that, and it was only the old one that was doing that. Doh!

So, I replaced it and all is well. :)

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