Irrigation Mystery

PetethepilotDecember 13, 2013

As an avid 'Do It Yourselfer' I love solving a good home maintenance mystery, usually with the help of the Internet. But I have an irrigation issue that absolutely defies any explanation. Just one zone of the ten in my yard's system will turn on normally and run for as long as 1 minute 15 seconds, and then pressure dies while the Pressure Vacuum Breaker pulses large gushes of water from just under the cap onto the ground. This happens whether I open the valve manually or with the controller. Adjusting the flow rate up or down also makes no difference. The remaining nine zones work normally.
So far everyone I've talked to maintains that it is not the PVB because the other nine zones work normally, and it is not the zone valve diaphragm, because it works normally initially. It must be a leak they say, but I have searched extensively any kind of leak or wet spots and cannot find any. Plus I've had several leaks before and the PVB did not gush water nor did the zone operate normally for any length of time before malfunctioning.
The system is 23 years old, I built it myself, and has the following components: Rainbird PVB 150 (1.5") and Randel 216PR zone valves.
I'd welcome any opinions or ideas that might solve this mystery. So far I can find no one on the Internet that has had an identical experience.

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Are you on a well and what type of flow (gpm) are you running that you need a 1.5" PVB. Are the valves also 1.5"

    Bookmark   December 13, 2013 at 5:40PM
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Thanks for taking the time to reply. Yes I'm on a well, the incoming and outgoing PVB is 1.5", but tomorrow I'll check the valves and stations to give you an accurate reply on those. (Pretty sure it's stepped down to about an inch). I have a method to determine the GPM (I know it's 20+) but it is involved, I'll do it if you think it's important. The system has supplied 6- 360 degree 30' hunters/zone very well for the last 23 years. This one zone however has far more and much smaller nozzles.

    Bookmark   December 13, 2013 at 6:39PM
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Just for your information, a 1" Pressure Vaccuum Breaker would have been ample size for 20+ GPM.
You stated that all other zones operating through that PVB are operating correctly. That should eliminate any partially closed, clogged shut off valve or filter which may be located before the PVB. A PVB needs a certain amt. of pressure at the poppet to keep it sealed and prevent flushing water from under the bonnet assy. That being said, I,m thinking that you may have a rather large leak somewhere in the zone piping. What may be happening is that when you start that zone the pump pressure switch is at its high end but as the water travels
through the zone and the break/leak? the flow is increased because of the break and as the flow increases the pressure switch is moving to it lower end and maybe below it. This may cause the poppet in the PVB to loose its seal and drop down, causing water to gush from the PVB. Watch the guage when the zone is operating and see if this is what is happening.

    Bookmark   December 13, 2013 at 9:08PM
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Well, good news. I found the leak. I did exactly what was recommended, and blocked all 25 (low volume) emitters in zone one, and did a walk through after turning the zone on. But the mystery continues. Initially the entire zone was bone dry, so I went back to the source, the PVB. And water was bubbling out of the ground about 2 feet from the PVB. The PVB was not pulsing water as before, even after several minutes. The reason I didn't see the leak before, is because when the PVB was pulsating large amounts of water out, it was over the area where the leak was. The 'Mystery' as I see it, is that the leak is long before the zone one valve. And the remaining nine zones still operate normally, with absolutely no water at all leaking out of area I found severely leaking when zone one is on. Could be that only zone one builds up enough pressure to separate a big crack in the PVC underground. Give me a few days to repair the leak and recheck everything, and I'll let everyone know what I found and if everything is back to normal.

    Bookmark   December 16, 2013 at 10:39AM
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Waiting to hear what was done to fix your problem. Let us Know

    Bookmark   December 27, 2013 at 3:43PM
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Sorry about the delay. Christmas and visiting family was (still is) a bit overwhelming. Hope the pictures come through (3). The leak was in fact confined to zone one. (All mysteries are now solved). There were a few more 'emitters' that I had forgotten about. (About 20 total in the one narrow but long winding area). As you can see, a weed (it was attractive, looked like a some kind of palm, so stupidly let it grow) grew so big it cracked the 1" PVC supply line.
Cut the root out with a chain saw and repaired the break. Everything working normal now. I am so grateful for the education and recommendations you all gave. This kind of forum is a real blessing.

    Bookmark   December 27, 2013 at 7:19PM
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Photo 2

    Bookmark   December 27, 2013 at 7:21PM
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Photo # 3. The fix!

    Bookmark   December 27, 2013 at 7:23PM
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a "mystery" no more, good job

    Bookmark   December 27, 2013 at 11:22PM
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