what is an irrigation master valve?

A master valve is an electric valve installed at the supply point which controls water flow into the main piping system. When this valve is closed water will not be supplied to the irrigation system.

A master valve will greatly reduce any water loss due to a leaky station valve because the leaky station valve can only leak while the master valve is providing pressure to the system. Also, if you damage the irrigation main line, a master valve will control water loss so the main can be repaired without shutting off the water supply.

A master electric valve is typically the same type of valve as you would use for your station valves, but rather than being installed downstream from your main line and connected to a station output in your controller it is installed upstream at the front of the main line and connected to the "master" or "pump" connection in your controller. Not all controllers support a mater valve or pump- be sure to check the features before buying a controller.