Master valves are a valuable addition to an irrigation system. But what are they? How do they work? And which features are essential? A master valve (MV) is an automatic solenoid valve wired to a sprinkler controller or pump relay. Its primary function is to control the flow of pressurized water into an irrigation mainline. To fit the needs of demanding residential and commercial applications, master valves are constructed of various materials, including glass-filled nylon, plastic, or metal. They’re usually arranged in a globe or angle configuration. It’s important to note that anti-siphon valves should never be used as master valves. Applying constant pressure on both sides of the valve, as required for a master valve, could cause it to fail or burst.

Valve Sizes and Features

Master valves range in size from 1 to 8" (25 to 200 mm). They’re located between the water supply and the irrigation system, often called the point of connection. In large systems, use a slow-opening and closing master valve to prevent water surge. To ensure reliable, long-term performance, opt for additional features such as pressure regulation, enhanced debris tolerance, and reclaimed water tolerance. Master valves are often coupled with a flow sensor. This invaluable tool can detect breaks in the system, which minimizes water loss and property damage. The flow sensor is sized for expected flow rates and may be a different size than the mainline or master valve. The controller interprets the flow sensor signal and uses it to detect flow conditions, such as overflow or underflow. Depending on the type of controller, the system may be able to stop irrigation, perform diagnostics, and send an alert to the irrigation manager. Not all irrigation controllers are compatible with a master valve or flow sensor. Those that are may work only with specific models. Check with your manufacturer for their recommendations.

Valve Type: Normally Open

A normally open master valve (NOMV) is in a constant open state. This allows the mainline to remain continually pressurized, regardless of downstream use. It closes only when a signal from the controller activates the solenoid and directs the valve to close. An NOMV is not energized during regular irrigation and can be subject to sticking. To ensure it functions normally when needed, it should be examined periodically to keep the moving components from freezing in the open position. A benefit of an NOMV is that it allows access to the pressurized water at any time for other uses, such as hose bibs, quick couplers, pond fills, and pools. This kind of mixed use can be challenging, however, if a flow sensor is also being used to track and manage flow. One downside of an NOMV is a lack of protection for the water source if the power fails. The irrigation mainline will also be exposed to any water surge in the water supply line.

Valve Type: Normally Closed

A normally closed master valve (NCMV) keeps the mainline isolated until the controller sends a signal that activates the solenoid and opens the valve. It activates when the first remote control valve opens and remains in that position until the last valve in the cycle completes its run time. This way, the mainline is pressurized only when the system is irrigating.

Since systems often run during night hours, small leaks that would be visible during the day may go unnoticed. Fortunately, a properly calibrated flow sensor can help remedy this issue.

In cases of fire, flood, earthquake, and other disasters, an NOMV can provide essential protection. In the event of a power outage, the NOMV will stay closed and will isolate the mainline from the water supply. This is crucial when protecting precious water resources during emergencies and preventing catastrophic site flooding if lines are damaged.

It can also help protect the irrigation system during the startup of utilities that were previously shutdown if the supply main is highly contaminated with debris. This allows the debris to flush out of the system before opening the irrigation lines. Based on these facts, it’s easy to see why isolation of the irrigation main using a master valve is a smart irrigation practice.