Question
I have 8 zones. Seven of them are working five.
Whenever I turns on the second zone, the water starting to shooting out for a couple of seconds. Then the circuit breaker trips.  About an hour later I can reset the breaker and the controller will work for other zones. The fuse did not blow out. I did not have this problem until I replaced four popups with risers (2 four feet and 2 two feet)shrub heads.  There are a total of 8 heads in this zone.  It may be just a coincidence.  Thanks for your help. Tam

Answer
Replacing the sprinklers should not be the problem.  I would suspect a faulty solenoid, the cylindrical device on the valve that the wires are attached to.  Make sure also to use water proof wire nuts when replacing the solenoid.  Also shut off the water to the system.