Thanks for the reply Larryglz. Your second assumption is correct, my 2 commons are independent for each 8 zones.
Sorry, looking back at it, my first post isn’t very clear. I’ll try to describe it better:
Let’s just say I have 1 controller. I want to be able to water twice as fast, so 2 zones on at the same time.
Here are some photos that may be helpful.
The photo with 1 controller has all 8 zones used, with 1 common wire. I think it’s a pretty standard setup. I can only water 1 zone at a time. (If I wanted to water more than 1 zone at a time, I would have to disable sequential flags and schedule start times manually for 4 zones. Or I could connect two wires to one port. Those solutions are too troublesome for how I use the sprinklers.)
The photo with 2 controllers is how I think it would work best for me, as long as it works electrically. That’s my stumbling block. I want to split the 8 zones between 2 controllers. Then, can I just jumper a common wire from 1 controller to the other, like I have the bare copper wire in the photo?