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Irrigation Master Valves
A master valve is an automatic valve, typically an electric solenoid type valve, that is installed at the point where the irrigation system connects to the water supply. The master valve is wired to a special "master valve circuit" on the irrigation controller. (Sometimes this circuit is called a "pump start circuit". Both types of circuits work similar or identical, and can be used for a pump and/or a master valve.) The irrigation controller turns the master valve on and off. Most, but not all, irrigation controllers have a master valve circuit built in to them.
How a master valve works:
Zone valves are the individual valves that operate a group of sprinklers or drip emitters. A typical irrigation system has several zone valves. Typically one zone valve is turned on at a time, and controls the irrigation in a specific area of the yard. 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 back up 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.
Benefits of master valves:
- If a zone valve develops a leak, or doesn't close, the master valve will act as a back-up to shut off the water. Note that the water will still be on as long as any other zone valves are on. But when all are finished watering, the master valve will shut off the main water supply to the entire irrigation system. While this does not eliminate the water loss or damage, it may minimize it.
- If the mainline pipe (the pipe from the water source to the zone valves) breaks, the water will be turned off at the end of the irrigation cycle and this may minimize water loss and damage. This is especially useful if the mainline is on a hillside, where a leak might cause massive erosion and property damage. Again, the water will still be on as long as any other zone valves are on, so it only will stop the flow when the entire irrigation system is off.
- Some of the more expensive irrigation controllers can use a flow sensor in combination with a master valve to detect leaks and shut off the entire irrigation system. The controller memorizes how much water is used by each valve zone. If the flow sensor shows that the water use is higher than expected, indicating a leak, the controller detects the change in flow and closes the master valve. Unfortunately, most commercial landscape maintenance companies I have dealt with do not know how to use one of these sensor systems, and they disable the sensor. This has happened about 90% of the time on projects I have used these systems on.
Disadvantages of master valves:
- Leaks are more likely to go unnoticed and not get repaired when a master valve is used. This is because most irrigation systems run at night, when nobody is around to see the leak. During the day, when the irrigation system is shut down by the master valve, the leak is not noticed and goes unreported. My experience is that most property owners, homeowners and, yes, even professional landscape maintenance providers, do not regularly check the irrigation systems for proper operation. They make repairs only when damage becomes extreme or someone complains. No, this is not how it should be done, but sadly it is what I see 90% of the time. For this reason a master valve can actually increase the amount of water wasted when a leak develops.
- Master valves lead to premature failure of both PVC and PE (poly) mainlines. This is due to the stretching and contracting of the pipe each time the system is pressurized and then depressurized. This problem is greatly exaggerated at higher water pressures (over 65 PSI or 4,5 bars).
- A master valve can increase the severity of water hammer if the mainline has a pinhole, or one of the zone valves has a slight leak, or if the zone valves close slower than the master valve. This is due to the water draining out of the mainline. When the master valve opens and the pipe refills, the water charges through the empty pipe at a very high velocity, slamming into the tees and ells and causing damage to the pipe system.
- A master valve is one more item that can fail and require maintenance, plus it adds to the initial cost of the irrigation system.
What type of valve should be used for a master valve?
Any electric solenoid valve can be used as a master valve, except for anti-siphon valves. Anti-siphon valves may not be used as master valves. (You should never install an anti-siphon valve in a location where there is another valve downstream of it, if you do it will break the anti-siphon part of the valve.) Many professionals like to use brass valves for master valves due to the higher pressure rating and a general attitude that "if it's brass it must be better". I don't feel that a brass valve is necessary unless you can't find a plastic valve with a high enough pressure rating. Note that the pressure rating of the valve should be at least double the expected water pressure in the irrigation system. So if you have 75 PSI, or 5,2 bars, of water pressure the valve should be rated for at least 150 PSI, or 10,4 bars. If the master valve is installed before the irrigation system filter, then a "contamination-proof", "self-filtering", or "dirty water" valve would be the best type of valve to use as the master valve. These are expensive valves that have a small built-in filter to help protect the valve from dirt, which is a major cause of valve failure. If a valve with a filter is too expensive, a valve featuring a "self-cleaning metering rod" or "self-flushing ports" would be the next best thing. At a minimum the master valve should be equal in quality to the zone control valves. I typically install a filter upstream of the master valve, so most of the time I use the same valve model for the master valve as I use for the zone control valves. If you are designing an irrigation system that uses hydraulically operated zone valves, you will want to use a hydraulic operated master valve rather than an electric solenoid type. Hydraulic operated systems are rare, so if you don't know what I'm talking about it doesn't apply to you!
Where to install the master valve:
The master valve can be installed anywhere you would like. It can be before or after the backflow preventer and or the pressure regulator (if used). A few water districts do not allow any valves to be installed before the backflow preventer, but most don't care. I typically place them in an underground box after the backflow preventer and the pressure regulator. In most cases, putting it after the pressure regulator allows the use of a less expensive valve with a lower pressure rating. In freezing climates the basement, utility room, or a heated shed is a good place for them. If you need to repair the master valve it will spill water when you open it, so make sure it is not installed in a location where a little water spilling out will cause harm. Some master valves spit water out of the valve when they are manually turned on. I suggest that the master valve not be used as the emergency shut off/winterization valve for the irrigation system. Use a separate ball valve installed before the master valve for that. Like all electric valves, sooner or later it will need to be repaired, and you will need to shut off the water while you fix it.
My opinion; when should you use a master valve?
If your mainline is located in a place where a leak might cause severe property damage or a danger to the public, you should use a master valve. If you are willing to pay the price of a flow monitoring irrigation controller with a flow sensor, a master valve can be used as a water conservation measure. The controller should be programmed to shut the master valve only if a leak is detected, and not at the end of every irrigation cycle. For a typical residential irrigation system, and even many commercial systems, I don't think the benefits of a master valve outweigh the risks or justify the cost. Many water districts in areas with limited water supplies require the use of master valves as a water conservation measure. I absolutely oppose the use of master valves as a water conservation measure when not used with a flow sensor and appropriate irrigation controller. My experience indicates they actually result in an increase in wasted water!
Text and Images by Jess Stryker unless noted. Copyright © Jess Stryker, 1997-2011. All rights reserved.