Sprinkler zone lost pressure and now triggers backflow preventer?

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cabootle

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Hello,
I have been driving myself crazy trying to figure this one out the last couple of days, and I am hoping someone here might have some advice before I call a professional.

I have a relatively small lawn (~800 sq ft) with about 12 pop up sprinklers, and two days ago I moved a sprinkler head about 5 feet which I did by adding a 5ft section of swing pipe (maybe not the ideal method, but I don't see why it shouldn't work). After making the extension I went to test the system and suddenly there was extremely low water pressure (none of my pop-up sprinklers came up, and water barely leaks out of them).
Thinking somehow extending the sprinkler in the way I did might have caused this, I removed the 5ft extension to get the system back to how it was when it was working before, but the problem persisted...

To troubleshoot I have tried the following:
  1. I double checked that all of my valves are open all the way. Main water to the house is on, and I have not noticed any difference in inside water pressure. Back flow preventer valve is open, and I checked there is definitely pressure at the release valves on the back flow preventer (how much pressure I am not sure, I do not have a pressure meter). I manually opened the sprinkler control valve, and water was flowing, I'm just not getting the same pressure I had before.
  2. Next I searched for leaks. After running the system for ~10 minutes (I have done this multiple times) I have been unable to find any water bubbling up, or any indication of a leak. I even dug up my lines around where I had extended the sprinkler to make sure I had not accidentally pulled it loose somehow when I did my work. I am fairly confident there are no leaks, but maybe it's deep and isn't apparent on the surface? I'd like to rule out anything else before I dig more...
  3. To ensure the control valve was not the issue I first swapped the internal components of the valve with a second one I had, but this made no difference. I even completely removed the internal components, resealed the valve, and ran the system this way to rule out the control valve reducing the pressure (my understanding is that this should allow water to flow completely unimpeded through the valve without the diaphragm/ internal mechanisms restricting the flow. With the full flow there was still not enough pressure to pop the sprinklers up.
Strange backflow preventer behavior I have noticed:
  • For some reason when I would open the control valve using the little screw pin it would trigger the backflow preventer valve. Opening it by unscrewing the solenoid or using the normal control system did not trigger the backflow preventer, however, today when the system turned on with the timer the solenoid activated the backflow preventer. I also noticed that the backflow preventer would activate when I removed the guts of the control valve and let it flow freely (I would slowly turn on the water at the vertical backflow preventer valve, and I could get it halfway open before the backflow valve activated). I took apart the backflow preventer and did not notice anything looking broken or out of place. Does the activation of the backflow preventer point to some problem I am not aware of? I think this is my last hope besides digging everything up to look for a leak.
Thank you for any insight or suggestions!
Chris
 

WorthFlorida

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I’m really not sure what is going on with the back flow preventer. What model or type is it? Is it easily possible to open the line before the back flow and turn on the water? When you moved the sprinkler, did you turn the water off before the back flow? Is there a shut off valve? I’m assuming you’re on city water.
 

cabootle

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I’m really not sure what is going on with the back flow preventer. What model or type is it? Is it easily possible to open the line before the back flow and turn on the water? When you moved the sprinkler, did you turn the water off before the back flow? Is there a shut off valve? I’m assuming you’re on city water.

Thank you for your reply WorthFlorida!

It turns out that the strange backflow preventer behavior was a good indication for a flow problem from the city. It turns out that my home had the correct pressure from the city (hence me being confused that it seemed like pressure was good everywhere else with lower flow than the sprinkler system -- e.g. in the house), but apparently there was a block in the mainline that prevented the correct flow. It turned out to be a huge coincidence that it occurred at the same time as when I moved the sprinkler head.
 

cabootle

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There was a block from the meter to your backflow or before the meter?

Before the meter. City had to come out, dig up the road, and cut the main pipe where they discovered there was some liner on the main that wasn’t supposed to be there. The liner would lift back where the branch to my home is, and so the pressure was there, but the liner would restrict any substantial flow.
My best guess as to why I didn’t notice bad pressure/flow with anything else besides the irrigation is that since I am in a newer home all of the faucets and showers are low flow water saving devices, so there wasn’t enough flow from those to notice.
I probably would have noticed if I had tried to use the tap while running the sprinklers, but I was outside all the time when trying to fix the sprinklers...
 
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