Russell Batemanlast update:
...though I have owned a number of brands over the years. Operationally, a
sprinkler valve consists of three controls. I add comments about them here:
I have owned valves that didn't possess a flow-control valve. I can't remember
how flow-control was regulated, but I'm pretty certain that less expensive
valves simply come wide-open with no adjustability.
This is entirely a problem at the valve. There's a easy solution to it, if it
works, or another, more involved solution. You should try the easy one first.
Turn bleed screw counterclockwise a bit to flush the valve (don't unscrew it
all the way—see warning higher up on this page). This should flush out
tiny debris holding the valve open so that the zone doesn't continue running
when turned off (at the controller).
If this doesn't resolve the issue, it's probably the diaphragm that needs to be
replaced or, at least, cleaned. Here's how to replace it.