@DLane, Thanks for your ideating. In answer to your question, I am not currently using the master pump circuit.
@emil, Thanks to you also for your ideating. That Doubler device appears very useful even as I still can’t get my arms around how it actually works. I do think your explanation of master and slave does explain my use case.
Restating the desired use case differently, I am looking to add a second inline valve that when closed would limit watering to just the first section of an existing zone. That first zone is a garden bed that would be watered more frequently than the remaining larger section.
Your combined ideating has sparked a new idea on my part:
What if the first zone powers only the first valve and I double lug the second valve and a pigtailed first valve lead to a second zone on the Rachio controller?
In theory, when the first zone is powered on only the first valve would open and water would be limited to the first garden bed. When the second zone is powered on both valves would open providing water to the garden bed and all the other heads of the entire zone.
Is this possible or would the power flow back from the pigtailed first valve lead back to the Rachio lugged second valve lead causing the second valve to always be open when either zone is powered on?
I do have extra conductors available on the wire going to the new valve if that could help.
Thanks in advance for your continued assistance. I feel like we are close to solving this puzzle.