I have reworked and repiped my sprinkler system, and fixed all the leaks.

Now when I turn the ground water pump on, I have good flow and spray from
all the heads, except three heads. These three heads are not at the end of
the run - well, one is, the other two are in the middle of the run.

The only thing common between them, is that they are all for shrubs, so
instead of pop up heads flushed with the ground, I had 18" high risers then
the spray nozzle on top of it. All three of them have no flow coming out,
just droplets of water, while the rest of the heads sprays perfectly.

I unscrewed one of them and water shoot out, over 10 feet in the sky, so I
have pressure there.

Is it because of the extra height of 18" in the riser causing the nozzle not
to spray?

Thanks,

MC