A master valve is an automatic valve that is installed at the point where the irrigation system connects to the water supply. (Sometimes this circuit is called a “pump start circuit”. Both types of circuits work identical, and can be used for a pump and/or a master valve.) The controller turns the master valve on and off.
Zone valves are the individual valves that operate a group of sprinklers or drip emitters. A Hydrawise controller supports 6 or 12 zone valves, depending on the model. Typically one zone valve is turned on at a time and controls the irrigation in a specific area of your garden. Whenever one of the irrigation zone valves is told to open by the controller, the controller also signals the master valve to open. So the master valve is a little like a backup valve or a fail-safe valve. The purpose of the master valve is to shut off the water to the irrigation system when none of the zone valves are operating. The image below shows a master valve operating connected to Zone 12 on a Hydrawise controller.
Water to zones
24V AC plug pack
With a Hydrawise controller, any one of your 6 / 12 zones can be configured to act as a master valve. The master zone is configured on the Zones & Schedules page above your list of irrigation zones.
Initially, there is no master valve configured and all zones on the controller can be used as normal zone valves. To select a master valve, select the relevant zone from the list next to the text which says Master valve.