Ok, suppose you don't have pressure regulated valves. Why would it be wasteful to install a pressure reducing valve on the mainline? Seems to me that it would be more cost effective than replacing the valves. As for the well over 100 PSI, I find that quite frequently irrigation installers will use a pressure regulating valve on the mainline over regulated valves almost every time. Which one is more likely to fail first? If a plastic valve gives way, or the pressure regulator is not set right, bam, there goes all of your heads and pipe about 200 feet into the air. A preset pressure regulator right off of the mainline near your point of connection is far more reliable. Most of them come preset anywhere from 50-70 PSI. Im sorry but I don't agree with you on that one, unless you can show me how it is more effective another way.
Tony Posey
Ridge Run Landscapes