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What is a Master Valve?

By T. L. Childree
Updated May 17, 2024
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A master valve is an electrically operated automatic valve that is often installed near the main water supply of an irrigation system. This device is usually connected to a specific circuit located in the irrigation system’s control panel. This circuit opens the master valve whenever a particular zone valve is opened, and then closes it again when the zone valve is no longer open. The primary purpose of a master valve is to prevent unnecessary water loss from leaky zone valves. Most irrigation system control panels have a special built-in circuit for this purpose.

A typical lawn irrigation system will often have several different zone valves that operate a particular group of sprinklers. During a watering cycle, the system’s controller will usually turn on one zone valve at a time in order to irrigate a specific area of the yard. When a master valve is used in an irrigation system, it is opened by the controller at the same time that the first zone valve is opened, and then closed again after all areas of the yard have been watered. A master valve is usually the same type of valve that is used as a zone valve, except that it is installed upstream from the zone valves as a type of fail-safe measure in the event of a downstream leak.

Some irrigation systems utilize an additional device to further reduce the possibility of water loss caused by leaking zone valves and sprinklers. This device is known as a flow sensor, and is able to signal the controller to shut off the water supply anytime a leak is detected. In this particular type of configuration, the controller is able to memorize the water use of each zone valve using information provided by the flow sensor. In the event of a leak, the flow sensor will show an increase in water use prompting the controller to shut off the water supply by means of the master valve.

Using a master valve in an irrigation system can sometimes allow leaks to go unnoticed for long periods of time. Since most lawn irrigation systems typically operate late at night, there is often no one present to notice that the system is leaking. In the daytime when people are around, the leak goes unnoticed again because the master valve has shut off the water supply going to it. Using this type of valve in an irrigation system may also cause a premature failure of certain types of plastic pipe. This failure is usually the result of the frequent stretching and contracting of the pipe that occurs each time the valve is opened or closed.

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