Water pressure surging in one zone

[MPGI]

Greetings!
I am a new member and have a question about my lawn irrigation system. It has four zones but only zone two has a full-pressure issue. Zone 2 comes on immediately when the timer switches but it oscillates. I can hear the pump cavitating. After about two minutes, it seems to come up to full pressure. Frequently, during the 40-minute run, pressure will briefly drop and then return to full pressure.
Thank you in advance for any assistance!

 

[WorthFlorida]

How many sprinklers and what type? Is it an irrigation pump or other type that uses a pressure tank? Is it a well or lake drawn water? I'm suspecting the well cannot handle the water demand. When pressure drops and then increases that could be how long it is taking for the well to recover. Another possibility is the pump is sucking air and losing prime. But with one zone, maybe not. Many pumps are self priming with just a small amount of water in the propeller area.

 

[Sponsor]

 

[MPGI]

Hi WorthFlorida,
Thanks for responding. It is a four zone system, with a shallow wellhead. I live along the coast and we only have sand so the wellheads in this area are pounded down just a few feet. One thing for sure, working on a sprinkler system in this sand is a dream. I considered it might be the screen on the wellhead getting fouled as they tend to do over time but ruled that scenario out since the sporadic cavitation only occurs in zone 2. Sometimes, there is no cavitation and the zone runs normally as the other zones always do. I am suspicious that it might be the zone 2 valve but the valve is 'downstream' from the pump. Hum.
I thank you for responding and appreciate any ideas. I also am grateful to Terry Love for having this site!

 

[Reach4]

I suspect zone two draws more gpm.

 

[MPGI]

Whoa, I never considered that. This spring, I fully opened two outlying heads to irrigate two raised gardens. I will shut down those heads tomorrow and see what happens. Good clue. Thanks Reach4!

 

[MPGI]

Okay problem solved! Yep, by opening the two extra heads (high flow) for the raised gardens it appears I overdrew that zone's 'bank account.' Sometimes in life, I encounter a forehead slapping moment and ask, "How could have I missed that?!" Thank you Reach4 and also WorthFlorida for responding.