Question
Hello,
Since repairing a leak in one of my valves (2 boxes, 3 valves ea.) when the systems tries to shut off at the end of a cycle, the knocking, slamming begins.  The valves seem to switch back and forth, shutting and opening and each time a loud slam goes through the main into the house. (Sounds like somebody is trying to kick my front door down).  My understanding is that since the tap for the stop and waste and sprinkler system is before the pressure regulator in the house, that I will need to add a regulator to the line after the stop and waste but before the valve boxes.  All of this pipe is underground and so to do so I will need an underground regulator that maxes out at 70 psi.  Where can I get one of these and does this sound right to you?  
Regards,
Erick

Answer
Hey Erick, I hope this helps. A pressure regulator would help if your pressure is too high. Any Irrigation supply store, or plumbing supply store would have a regulator. Also, what you can do is install it in a valve box, just like the valves are in. You need to know what size mainline is feeding your valves, to determine what size regulator you need. I would also recommend getting one that is adjustable ( 50psi to 100psi), so you can increase or decrease the pressure if need be. Good luck and have a great day.