According to the specification of the valves, it consumes 1.2A current @ 24VAC, so it’s a little bit beyond the capacity of one single channel on OpenSprinkler (rated at 800mA max). But I am pretty sure you can combine two channels in parallel to increase the current output. Specifically, one wire from the valve goes to the COMMON line as usual, the other wire will connect simultaneously to, say stations 1 and 2 (the best way is to use two separate short wires from stations 1 and 2, then solder them and join them with the valve wire). Next, it’s important to always schedule stations 1 and 2 together (you will have to turn ‘Sequential’ mode off so that stations 1 and 2 can be activated at the same time). This way, stations 1 and 2 will simultaneously open to share the current load.
Alternatively, you can replace the current triac with a beefier traic that is rated at 1.2A or above.
The last solution, which is safer (given that these valves are very expensive) is to use a relay. Specifically, OpenSprinkler will control a relay, which in turn opens or closes the valve. You can either use a single 24VAC power supply, in which case the relay should be a 24VAC relay; or you can use two separate power supplies (so that one power supply powers the controller, the other is 24VAC that powers the valve).