SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

I have a well pump just for sprinkler system, nelson brand for about 14 year old
last year I winterized myself, and notice zone 5 was not much water coming out.
this spring zone 5 has low pressure, although the sprinkler head popped up, and the water can come out, it is no mist at all. I tried to clean the zone 5 valve myself, no use, I can't tell whether the valve is good or not. I also measured the pressure while the zone 5 is on by attaching the pressure meter to the well water faucet outside the house, and it read 20psi. The other zones have 40psi...
Does this basically indicate that I have a leakage at the zone 5? if so, how can I find where it might be?
I changed one of the sprinkler heads last year in zone 5 using Hunter PCP, the pressure at that time was OK...

Your advice and thoughts are really appreciated.