Question
This is a weird one, and not the obvious "broken sprinkler"
question, so bear with me as I try to explain this issue which is
driving me crazy.

We bought this home new three years ago, and watched it built
from the ground up. All new plumbing and sewage in all cases.

We installed sprinklers in our back yard two summers ago, and
they worked perfectly for the past two years without a hitch.
These were added to the end of the main line that supplies water
to the front yard sprinklers. I just added 1" pipe to the end and
brought it to the back yard and continued with two more
stations with six valves on each station

This spring, they all stopped working correctly. No pressure to
pop all the heads out of the ground and just a trickle of water
coming out of all three stations.

I immediatly assume that a line must have broken somewhere,
so rather than digging the lines up,  I installed ball valves after
station one and two and try turning off each line to find the leak.
Still no pressure.

I repeated this with station two, and put a ball valve in line on
the main immediately after station one, and got the same result,
still no pressure.

This would lead me to believe that none of the sprinklers after
station one, or the main line that supplies water to all the
sprinkler valves is ruptured.

The weird part? When the sprinklers are turned on, the pressure
in my house drops dramatically. When we turn the sprinkler test
off, it builds again. Thishappens on allsprinklers in the yard, fron
t+back.

When I turn the sprinkler master turnoff to the off setting, all
pressure in my house is fine. When I turn the sprinkler master
turnoff back on, I still have full pressure in my house. Then I
turn on one of the sprinkler lines  from the control box, and it
doesnt pop the sprinklers up and the pressure in my house
drops again.


Any thoughts?


Answer
Lee,
 This is driving you crazy, Isn't it? You did a lot of work here, gave me some thing to work with. You say that you put the shut of valve after the valve you added. I think the thing might be that the leak (maybe) is before the isolation valve(s) you put in. It's on the piece of pipe you added on took into the back yard. To figure this ou8t with digging just turn the water off at it's tap or shutoff, wait 15-30 second and turn the water back on, if you here water running something is leaking on the 1" inch pvc you put in. The other thing you can check is to make sure the valve that is in your house that is the main supply valve to your house, that is not the valve for the sprinklers is open all the way. Also check the valve that turns the sprinkler on and off is open all the way. I do not know if the sprinkler on off valveis inside or out in the ground, but if it is inside and you turn the sprinklers on and you here a loud noise that sounds like restricted water, then something is not open fuuly or broken in the half closed positionj.. especially gate valves.

          Let me know, Jim