Leak with a master valve

Looking for advice to hunt down a small leak. No noticable leaks in valve boxes. Leak is about .15 gpm.

Setup is Weathermatic master valve that I just replaced solenoid because it was shorting and kicking Rachio off wifi. Working now.
Hunter valves on 5 zones. 2 in front yard 3 in back.

When I only run front zones no leak after shut off. If I run any of backyard zones leaks after shut off, but if I run front zone even for 1 minute after the back zones no leak.

Don’t know why master valve isn’t shutting flow off after backyard. Does this sound like an inner master valve issue or should I be trouble shooting the solenoids or sprinkler heads in the backyard.

Any advice to try to isolate the problem or other forums for advice would be appreciated.

You are 100% sure that the backyard is fed through the master valve? There is no logical reason why it would leak with back, but not front if they are all flowing through he same master each and every time.

Yes, the main irrigation line leaves the house and goes right to the master valve. I can hear the master valve open when running the back zones. The trick of running a front zone to shut it off always works. I was assuming it was a leak in the back but now am questioning why the master valve doesn’t seem to be doing its job.

I have a Flume flow monitor so can see the history and real time flow rate but have also confirmed the leak on the meter.

It just seems weird that one section would cause issues with the master valve, but not another.

It is pretty easy to pop the top off the valve and inspect the diaphragm for any issues or debris in the valve that might be causing an issue…

I guess that’s as good of a place to start as any. It really doesn’t seem to make sense but atleast I have a work around in the meantime.

when the leak persists, do you have any irrigation shut off valve (a manual, ball valve?) that you can turn off to confirm the leak stops? Is your flow meter an ultrasonic non-invasive one, or is it wet, inline with the irrigation system?

nvm, Flume is over the pipe ultrasonic. Where is it installed? is it after the master valve? is it possible that the front zone does not keep water after main valve shut off and water gets circulated from the back zone into the front zone and emitted out via whichever sprinkler head is losing it?

When it leaks I can shut off the manual valve to the whole irrigation system, inside by the main water line. Then the leak stops (or atleast no flow is shown on any readings) or just running a front zone stops the “leak”. My flow meter is ultrasonic/magnetic non-invasive and it is matching the rate displayed on my water meter.

ok so the Flume is before the irrig shut off and way before the main valve. And past the main valve you have zone valves. And water leaks only after using some valves.

With the master valve closed, can you manually open each individual zone, one at a time, does any get water? Thinking that in order for this to be a leak, that master valve has to not close fully.

Also, is the back yard zone higher gpm than front? is it possible that the back zone has a high demand and that sucks water from the house (ie it wants more gpm than your main provides). Thinking when a high gpm zone runs, if main cannot keep up, the irrigation system may start depleting your water heater and other high pipes in the home or water holding devices - then when you turn it off, the “leak” is simply the house refilling its pipes? wild theory - then running the front which is lower gpm allows the house to fill back up masking the “leak” under the guise of front zone running?

I guess let’s start with the basics, available gpm? front zone gpm? back (leaky) zone gpm?

one other test I would do… after running the back zone, let it “leak” - does the leak ever stop?!if it does, that is clearly a refill. Do you have a water softener in line with the irrig? or a large filter?

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The Flume goes right by the water meter. It is for all water that comes in from the town water supply not specific just to irrigation. It is before the sprinkler system main valve.

I’m not sure I’m following about keeping the water after mv shutoff? When the front section runs and mv shuts off flow meter go to 0 almost immediately. If any of the back zones are run last in a schedule and mv is supposedly shut off the flow rate will run at about .15gpm without end (has gone on for hours sometimes) unless I run a front zone.

This seems that water is “leaking” somewhere and being allowed to pass thru the mv because only when the front runs last the mv seems able to stop flow completely. Even if a head in the back is broken/leaking, shouldn’t the flow be stopped at the mv?

also, and sorry for the question barrage, do you have any backflow prevention mechanism between the house and the irrigation system?

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The “leak” will not stop if the back zones are the last thing run and I don’t do anything else. And no nothing else in line. Water supply comes into the house, runs through the meter and then splits off to irrigation and the rest of the house/water heater etc. If I close the irrigation valve “leak” stops so it’s definitely correlated with the sprinklers and not other water needs in the home.

ok, for water to leak aka be lost out of the system, if it passes the mv, it has to go somewhere. Either a leak between the mv and the zone manifold, or another valve (a zone one) being bad - that is, you need both mv and another valve to be bad - and if so, where does the water go?! .15gpm is equivalent to about 14”/hr on a 1sqft area, if it comes out a sprinkler, it should be a very visible puddle… or multiple smaller ones at each sprinkler

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cool, so that (house device refill) is ruled out.

backflow prevention device exists?

Questions are great. I’ve exhausted the little knowledge I have of what could be going on. Yes I believe this is back flow in upper left. It seems old and I hear a slight buzz from it but would need to educate myself on anything to know if it’s works properly.

ok, assuming that PVB has not been recently tested. Is back zone HIGHER ground than front?

the reason I am asking, if that PVB is broken and allows water return and you have a high sprinkler zone, it is possible for the water in the irrigation system to flow backwards. Not sure if Flume can detect flow direction - still a problem with neverending leak tho - you also need low main pressure for the reverse flow

The times I have inspected I have not found puddling in zone boxes or at the heads. I figured it was maybe somewhere buried in the lines but can inspect again but will have to let it “leak”. Given in your scenario that both the mv has to be leaking/failing and another zone I’m still confused as the why the mv wouldn’t be “failing” with the front run last. Is that the front probably doesn’t have the any leak so water is just not being lost/flowing thru the mv even though it could technically be stuck open? But in that case if the mv was leaking wouldn’t it still be able to the backyard and still leaking? Sorry if that is hard to follow just can’t figure out the front to backyard issue and what changes at the mv.

The backyard is basically level with the mv but the front yard and the front 2 zones box and heads slope down and away from mv and pvb.