I went to start up our sprinkler system today and everything went well except I have very low water pressure at the heads. They valve opens but the heads hardly rise out of the ground and I can piss farther than they throw water. It is the same for all the zones. All the pipe valves are fully opened and I don't see any water puddles any where on the lawn that would indicate a broken line. I walked the entire property and no puddles. It is the same for all the zones which suggest to me the problem is at the main water line. I replace the main valve in the basement last year so that shouldn't be a problem. I can hear good water flow. Could the back-flow preventer valve cause this problem. I took it apart but saw no obvious problems. Thanks for the help.