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When I turn sprinklers on, the water pressure is practically zero for sprinklers and also in house. Upon turning sprinklers off, house pressure returns to normal. Leak detection service found no leaks. Replaced house regulator. No change. Previously noticed that when sprinklers initially go on there is a bit of a vibration "jolt", which might be a separate issue. Next step plumber wants to take is to replace irrigation regulator...? My irrigation regulator is as old as the house. (Built in 1989).

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    Please edit to tell us more about the system and its history. New system? Suddenly started doing this? City water? Well water? May 24, 2020 at 15:38
  • Have you checked the backflow preventer? The water has to be going somewhere... May 25, 2020 at 11:18

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Not sure if the gentleman ever got his irrigation issue resolved but just wanted to post a possible solution.

We, too, had the same exact issue that you described and we went through 4 irrigation companies to no avail. We decided to try one more company that appeared to have more in-depth expertise and the technological tools necessary to render a comprehensive assessment.

After asking many questions and performing a few tests, the bottom line is the irrigation specialist suggested that we call the water company to have them perform a pressure test for the flow rate on our water line because he believed that there was a restriction in the main water supply. My husband call the water company immediately and they sent someone out in a matter of hours to perform a test and he, too, concluded that there was a restriction in the main line which he located. Apparently, a 3” piece of rubber tubing debris had worked its way through the main water supply line and because our home is located in a cul-de-sac at the end of the line, the debris eventually became lodged; thus, restricting water flow.

He removed the debris and our irrigation system began working again, actually even better than before.

Because our situation had the exact same symptoms as yours, I suspect that you, too, may have some debris in your main water line. It is definitely worth exploring, it will cost you nothing and can save you thousands in unnecessary repairs. Thought I’d just pay if forward.

Good luck

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Sounds like one or more large ruptures in the sprinkler buried pipes. Somehow the inspection missed it. You could check by turning on the sprinkler then looking at the water meter ; it should have some kind of dial to show if water is flowing.

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It could be a faulty safety pressure valve, f.e. used upstream of an electric/gas/oil boiler in the cold water inlet pipe.

In combination with the - assuming long - sprinkler lines/hoses, a sort of pressure (standing/reflected or other type of) wave could be established that opens this SPV periodically or permanently if the sprinkler is opened. The sprinkler itself could start that pressure wave if it is of a type that sprinkles intermittently.

Needing resonance, it would be only generated with the right matching length and cross section of hose/pipe.

The SPV could also be dirty inside. Many SPV have manual handles to turn/snap them open for a short moment in order to clean the valve.

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Perhaps try capping the sprinklers and see if the same thing occurs. A possible leak in the irrigation line would also be more obvious.

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Really sounds like large leak underground in the sprinkler piping.

How did said "leak detection service work"? What did they do? Here's what I would do:

  • See if the water meter spins when you turn on the sprinklers. This confirms water flowing. But that's almost certain.
  • How many zones do you have? If the pressure problem exists for one or two zones (or more) you may have multiple leaks. If you have many zones and the problem exists for all of them, the leak is probably between the main water connection and the valve box. This will help you find it.
  • Leave the system running for 10 or 15 minutes then walk around the yard looking for puddles or mushy places. A large underground leak will tend to show itself on the surface after not too long. Note if the leak is in the feeder line to the valve box, and if it is near your basement wall, the water may enter the basement rather than bubble up to the surface. Be ready for that.
  • You may be able to hear the leak if you walk around the garden. If there is traffic noise do that test at night when there is less noise.

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