It will all depend on the application. What are you watering? how are you watering are there any hazards? What kind of Hazard of contamination, chemicals, pumps. This will help determine you required backflow prevention device in addition to your local water authorities requirement.
Master valve designation is identical in material. It is the same valve, but it is located in the sprinkler system before all of the other valves, but after your backflow prevention device.
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