I have a 9V valves and I’m reading to setup OpenSprinkler with them. In my case, my valve is latching, and I think this is the problem to make compatible with OS software. My valve open circuit with a 9V positive pulse (just one pulse, not continue voltage) and close circuit with a 9V negative pulse (reverse polarity to open).
When working with pulses, I need to configure the valve with two tasks, one to open and another to close. Connecting a motor driver board to 2 GPIO pins, I can open and close, because the motor driver generates 9V and -9V depending on 2 GPIO pins.

So, all this talk about latching valve mode, I recommended a not latching valve, but I did not know its existence for 9V operate.