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

I have one zone in my 20 year old system that seems to have an underground leak.

The line from the manifold valve is 3/4 inch PVC with 1/2 inch flexible feedlines to 5 individual pop up Toro 570 sprinklers.
2 or 3 heads won't pop up fully and 20 minutes of run time generates mushy sod half way into the zone.
I winterized the system with my 100 psi compressor and couldn't get full water blowout at the one uphill head.
I am in the process of replacing all the Toro 570 sprinkler guts with new parts to assure good seals and smooth popup surfaces. I'll replace all the nozzles with Toro MPR+ 10' VAN 360 Adjustable nozzles.

When I get everything replaced I can pressurize the zone with air but don't know if that will tell me if there is still a leak when I run water to it in the Spring. We seem to be having an endless summer here in Colorado...

Bottom line question is how do I find a leak in the zone line or connections without excavating my backyard lawn?
I guess I can excavate around each head first to look for leaks when I replace the inner parts as well as assure tight fit on the risers. Do I then slice sod back along the feedlines checking for leaks at connections to the main line?

My other thought is to excavate up from the mushy area to the mainline and search left and right from there.

What professional tricks am I missing to solve this mystery?

Thanks

OK, good idea to shut off the nozzles in the zone.
I'll be using the TVAN 10 Adjustables and they look like leaving them closed should limit their flow to a dribble, right?
Doing this procedure in the Spring right at system startup should have really dry ground to work with.
So a break or loose connection should show up well.
I can set the controller to run the zone manually one minute at a time until the leak shows up.
Then it's a matter of sod surgery...
Got any recommendations for a good sod scalpel?

https://photos.app.goo.gl/EZahe3RAnDW6zac89

Well, good news and bad news.
I dug up the sod and found the leak.
Good news is it wasn't a broken PVC line.
Bad news is it was a failed auto drain valve (old age).
Please look at the picture showing the multiple system lines with the leaking zone at the bottom.
I decided to replace the drain valve with a brass plug to eliminate any further moving parts issues.
But I am just wondering if the next year I winterize the system enough water will be trapped in the fitting to cause a problem with freezing expansion?
I can hit the line with 100 psi several times but will there be enough water trapped in the plug fitting to cause a freeze failure?
Thanks...

OK, I understand old school compressor issue.
I'll be more careful limiting the tank pressure.

And I believe I can adapt my compressor output line to a garden hose configuration.
But how in the world do I connect the garden hose to my backflow valve?
I'm currently using the upstream test port with my air hose quick connect fitting.
Do I jury rig that test port from the quick connect to garden hose somehow?
Seems like I need to do the same as from the tank to garden hose in reverse.
My plumbing is 1" copper from the basement to backflow valve and from backflow to manifold PVC.
Thanks for the help...