Pulsating Sprinklers

[JeepinEd]

I'm trying to figure out what the heck is going on with my 4 station sprinkler system. Stations 1 and 2 seem to work fine. When station 3 is running, I can visibly see that the water coming out the of sprinkler heads is pulsating. It gets stronger, the weaker over and over with about a 1/2 second interval. Station 4 has the same problem but more pronounced. When station 4 starts, the pulsing is so strong that it briefly causes a water hammer effect on the pipes in my bathroom. I have already replaced the sprinkler controller, as well as the #3 and 4 sprinkler valves. I have also replaced most of the sprinkler heads, yet the problem remains. This is a fairly recent issue on a sprinkler system that had been working fine for years. I'm at a loss here, so any ideas are welcome.

 

[deadlyapp]

Do you have a pressure regulator prior to the valves that could be causing an issue?

 

[highland145]

Does it do it If you manually open the valves all of the way?

Well or city water?

 

[JeepinEd]

Does it do it If you manually open the valves all of the way?

Well or city water?

Yes, it still does it if I open it manually. City water. I tried using a volt meter to see if there is an oscillation in the voltage, but it was a steady 25.5v AC.

 

[herm0016]

could be junk in the valve, i would take the lid off the valve and clean.

 

[JeepinEd]

could be junk in the valve, i would take the lid off the valve and clean.

I tried cleaning the valves, to no avail, so I replaced the two units that are giving me trouble. Still the same issue.

 

[Micrornd]

I would start by looking for differences in the zones, it might help lead you to the real culprit.
It sounds as though 1&2 are about the same (length, # of heads, etc.) with 3 being slightly larger and 4 larger still ?
Perhaps the city water pressure has changed about when this started ?
deadlyapp asked about a pressure regulator but you didn't answer, that could also cause the problem.
Have you checked the pressure with a gauge on the sprinkler system ?

 

[JeepinEd]

I would start by looking for differences in the zones, it might help lead you to the real culprit.
It sounds as though 1&2 are about the same (length, # of heads, etc.) with 3 being slightly larger and 4 larger still ?
Perhaps the city water pressure has changed about when this started ?
deadlyapp asked about a pressure regulator but you didn't answer, that could also cause the problem.
Have you checked the pressure with a gauge on the sprinkler system ?

Actually 3 and 4 are smaller. I'm planning to purchase a water pressure meter this weekend. I can see the first sprinkler head on #4 rapidly going up and down as it sprays. I tried replacing that sprinkler, but it still does it.