SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

I have been servicing a friend's residential irrigation system...it was installed using poly pipe via vibratory plow, and has a variety of spray and rotor heads, all Hunter brand.



The problem is that about 50% of the heads have become unscrewed from their riser pipes...that means about 10 turns to completely unscrew the head.



I might possibly understand that a rotor head could eventually unscrew itself due to rotational torque, but since they rotate in both directions, that torque would seem to be self-canceling. Plus, the problem has involved spray heads as well.



When these heads start leaking from being unscrewed at the base, the head bodies are fairly anchored in the soil, suggesting that they could have not unscrewed themselves 10 turns...



My theory is that the original installer only engaged a thread or two when installing the heads, to insure future service calls...



Is there a less sinister explanation for all these heads unscrewing themselves?



[BTW, my personally-installed system has been trouble-free for 15 years...also Hunter heads, but Schedule 40 PVC rather than poly, but have never had a head unscrew itself]



thanks-



yes, my first post here, so be gentle.

Quoted from "Mitchgo"

Whats the water pressure to the system? High pressure is the usually the cause of this

The nozzles on the spray heads are extremely small threads..There are times with high enough pressure to pop off the nozzle of the spray head but not damage the threads.

No, I'm not talking about the nozzles unscrewing themselves, but rather the 3/4" pipe threads at the base of each sprinkler head. It would take about 10 turns of the head body to remove it from its riser-pipe...in all cases, I'm left with a head with a short, threaded nipple still firmly attached to the sprinkler head, but with the nipple completely unscrewed from the 3/4" female fitting on the riser...

Quoted from "mrfixit"

What happens when you screw them back in. Can you pull them out suggesting bad fittings? Maybe they over tightened them cracking the fittings?

All threads were in perfect condition, except for being filled with the local clay as a result of being completely unscrewed. No stripped threads, no cross-threaded connections, just 3/4" threads with only one thread-engagement, or, zero-thread engagement. They cleaned-up fine and the heads were re-installed and work fine.



I'm just questioning how the heads could have come unscrewed, and the only conclusion I have made was that they were never screwed in more than a turn or so during original installation.