Question
I have a system that has 4 zones that is hooked to a well.  I have had trouble with zone 1 since I've owned the home.  Zone 1 will not shut off after the sprinkler advances to Zone 2.  I've had 10 different companies come out and do a number of different repairs.  The system will work fine for the first 5 or 10 times after the repair and then Zone 1 continues to stay on when it cycles to Zone 2.  The valve has been changed many time, all diaphragms have been replaced many times, solenoids have been replaced.  The control box has been tested and it's working correctly.  I've asked the companies if they feel it could be caused by the well, maybe sand coming up and blocking the valve from closing all the way.  They don't feel this is the issue because they think all the valves would have the same issue, not just the first one.  One company told me that the diaphragm had been "blown out" (I'm assuming he meant the shape had been disformed)  I am wondering if the well has to much pressure and it's causing issues with the first zone because of the pressure.  Is this a possibility?  Any help provided would be appreciated.  

Answer
Yes the pressure is a possibility, can you send me info about the static pressure, dynamic pressure in each zone, valves models, valves sizes, pipe size. do you have a pump?
Have you measure the volts at valve 1 while valve 2 is running, should be 0vac if you have like 24vac this is the problem, in this case move the zone 1 wire to an empty port if its available.
Regards
Guillermo