HI Tom, Ray,
Our flow meter is a netafim flow meter we used for the cyber-rain irrigation controller. Most of these have what’s called a pulse reed switch that pulses the output after every gallon.
Should be able to just have a pull-up resistor connect to the switch such that the switch pulls the signal down when pulsed. If you count the pulses per time period you would know the flow rate.
With your newest design if you could have some area on the board to wire this in that would be great.
The flow rate when the valve is just turned on is not a good indication for leak detection. You have to wait until all the lines fill up and the air is out. This depends on many factors in your system but is usually 20-90 seconds. Then the system can sample the flow rate once stabilized and give a very accurate flow rate. It won’t find a very small leak, but does tend to find if a head is broken off or a pipe has a crack in it. It has helped us tremendously and saved us a lot of money by detecting problems early on.
One of the other posts someone mentioned using a pressure sensor for detecting leaks. I don’t recommend this. Most irrigation systems have a pressure regulator and it’s primary goal is to maintain the water pressure even if you have higher or lower flow rate. Maybe there are some isolated situations where a pressure sensor works, but we have had great luck with the flow sensor.
To detect leaks the best way we have found is to use 1 good flow sensor installed before all your valves. Then when you turn on a valve you can check the flow rate for that valve. Also if your yard has hose connections and someone leaves that on, it should see it as well – so for example if it see’s a flow rate for more than X minutes after the last valve is off then it could email you. Also this helps detect leaks in the main lines BEFORE the valves. And if a valve fails to turn on, you would get an underflow condition so you would know one zone isn’t working properly.