Sprinkler system issue

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
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They are probably just plugged or turned off. Try moving the adjustment screw, or remove them and reverse flush them with water or air.
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I agree with Bob, they are either plugged or the flow adjustment is turned all the way down. Remove the head and check for a plastic filter underneath. If it is present remove it and flush it with water and blow through with air. Also there is probably an adjustment screw on the top of the head, try turning that out fully clockwise and running water through it.
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wrote:

I agree with Bob, they are either plugged or the flow adjustment is turned all the way down. Remove the head and check for a plastic filter underneath. If it is present remove it and flush it with water and blow through with air. Also there is probably an adjustment screw on the top of the head, try turning that out fully clockwise and running water through it.
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It wouldn't necessarily be clockwise. Mine all open counter-clockwise.
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You are right. I was thinking upside down.
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MiamiCuse wrote:

http://irrigationtutorials.com/faq/heads-do-not-popup.htm
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wow, this is a very good link. Thanks a bunch!
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wrote:

They are not clogged. I removed them cleaned them and tested again, nothing. I think this has to do with pressure. If I take a head that does not spray and put them on a head that is on the ground, it sprays. If I move them back to the 18" tall riser, they don't. Strange.
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