Sprinklers won't reliably pop
I've fought my sprinkler system (lawn) for several years now -- it's only a problem on one line of four. It's apparently not getting enough flow to make all the heads get past the "blow-by" stage and pop. I've shut down three of the 9 heads, which has helped, as does having it run during the wee morning hours when there is more pressure. I've tried replacing the valve, made sure all the shut off valves are open all the way, etc.
I just tried to turn it on to water in some fertilizer and see a LOT of blow-by going on at the last head in the line. If I manually pull the head up to where it seals, the entire line (remember three heads are shut off) operates great and pressure seems fine. I've replaced that particular head and it appears to make no difference with the blow by issue. I know I could split the line and add another valve and zone, but that's expensive and a lot of work.
Does anyone have any other ideas? Is there a head that doesn't blow by before it pops up that I could try in that particular position?
Thanks for any suggestions!