trapped air in plumbing
My system goes from one line that is lower in lawn to another system that is higher in lawn. My problem is that air is trapped in the system and all heads now "pulse" several times a second as the trapped air moves from the high spot back to the head and then back to the high spot. Same thing happens in a house but there the plumbing can be cleared by opening the taps. My sprinkler system is restricted by the pressure at the heads.