Sprinkler pressure issue
I have a sprinkler system that gets water from the creek in my back yard via a pump controlled by a controller and pump relay switch. The system has 4 zones, 2 valves are clustered on one side of our yard and the other 2 valves are on the other side. (see attached diagram)
Now the problem, I noticed the other day the sprinklers on zone 1 were surging from a trickle back to normal spray constantly. I went to the pump and it was pumping normally but the PSI gauge was fluctuation over a large range. I switched to all the other zones and they all worked fine and had a normal operating PSI of around 38 PSI.
Another observation that may or may not be a factor, for years now zone 1 and 2 both made hissing noises as the rotors spray and it doesnt stop (sounds like air is escaping) Zone 3 and 4 do not hiss. I'm assuming Zone 1 and 2 are clustered via a manifold so I wonder if it could be a valve issue? I cant easily check them since the valves are just buried without a access box. Another note just as more background info, is that zone 1 and and part of 2 are both on top of a hill maybe 10 or 15 feet higher than the rest of the system but this has not caused an issue in the almost 20 years the system has been installed.
Here is a video showing the pressure gauge on my pump when zone 1 is running http://www.youtube.com/watch?v=ZsVwcU9j00Q (ignore the red needle, it just moves from the vibration)
We had a new pump installed about 5 or 6 years ago after the old one failed and we also moved the pump location and intake to a new location where the creek is deeper to reduce the work of the filter.
This is what possibilities I can think of, what do you all think?
1. Pump is bad (unlikely since all other zones work fine, although the start capacitor was being finicky a few weeks ago)
2. Break in the line for zone 1 (no super wet or muddy areas noted)
3. Valve is failing (still turns the srinklers off and on fine)
What would you recommend to troubleshoot this?