Beaten by sprinkler valves

[deadeye]

It's not often I admit defeat when it comes to general repair around the home but my sons sprinkler valves beat me today.  The system is 20 years old and has 7 zones.  For the past several years it' been a bitch blowing out in fall and getting it up and running in the spring.  Basically what happens is a number of valves (this spring all 7) do not close.  It doesn't matter if you select any particular zone, because they all are "on" (not electrically) and with them all on it just dribbles water out of the heads.  Back pressure is used to close the valve when the 24V AC is removed from the solenoid however, with all heads "ON" there is not enough water pressure to turn them off.  Catch 22.  Other years when only a couple zones had the issue we could eventually get them working by bleeding the valves or beating on them but with so little pressure we cannot get any to close. Anyone got an idea how to resolve this conundrum. 

[Leech~~]

Don't you have to take those heads apart once in a while and clean all the dirt, bugs and grass clippings out of them so they function right? 

[mike89]

rust in the lines???

[Gunner55]

DE, I spent many seasons working as a greenskeeper at out local CC & we had a Toro system there. Leech~~ & mikey are on the right track as when we had that problem we'd take the heads apart, usually it was just a plastic snap ring & the rotating part of the head would pop out. Under that was a plastic spring loaded ball seat vale that also had a plastic snap ring so it'd come out. At least 2/3, maybe 3/4 of the time it was the valve full of junk(dirt, rust) so we'd just put a different 1 in or pull that 1 apart to clean it. After having the same issue in many of the same areas a lot we started to start at the far end of the line & pull the head apart to check em. While it was apart we'd go back & turn that section of system on to blow the junk out of the water lines, then rebuild the head. Otherwise the new stuff we installed would plug again pretty fast. I'm not sure what system you have or exactly how it works but your issues sound very similar. You should be able to find some helpful info online

[Leech~~]

Don't forget the ones that don't go down all the way and get chopped up by the mowers!   

[deadeye]

Thanks for the ideas but it's not the heads but the VALVES that control each zone that are at fault.  I have rebuilt many heads but as Leech,, pointed out I could chop off all the heads and still have the same issue.

[Gunner55]

  Sorry, I misunderstood your problem.