First: What a great product !! This is my first post.
4) Please consider that flow meters have different units. For example here in europe usually there are flow meters with reed switches showing 1 Liter/Pulse, 10 Liter/Pulse, 100 Liter/Pulse (my has 10 Liters/Pulse).
And I have one idea for the main valve. At the moment I can not open the main valve alone, but that would be useful: I have water sockets on my main line where i can attach hoses. To use the hose the main valve must be open, but all other valves can be closed. That would be useful also for checking if the main line is under full pressure ok and there are no leaks. The solution could be to open the main valve on the main screen like every other valve for a amount of time. That would be good so it will be closed later and is not forgotten to close.
Finally one question: Is it possible to give 24V directly parallel to the main valve even when it is not opened by opensprinkler ? Or could that damage oopensprinkler because it is getting 24V on a valve port ? I am asking this to bypass opensprinkler to open the main valve for the mentioned water sockets/hoses. Or is there any other solution to open the main valve alone ?