Winterizing irrigation systems among crucial jobs as fall arrives

Updated Sep 17, 2019
Photo: ToroPhoto: Toro

If you live in a region that experiences freezing temperatures, it is crucial to winterize irrigation systems properly.

Systems that are not winterized often display the signs of damage in the spring. In winter, water left behind in the pipes will expand as it freezes, causing fittings and/or pipes to burst.

Winterizing an irrigation system is pretty straightforward and should be done before the first frost if possible.

The key purpose of winterizing is removing all the water from the irrigation system. This is commonly achieved by the manual drain method, automatic drain method and the blow-out method.

Since the blow-out method is considered the most effective way to ensure no water is remaining in the pipes, those steps are outlined below:

  1. Turn off the water supply.
  2. Attach the air compressor hose to the mainline by quick coupler, hose bib or other connection after the backflow device.
  3. Activate the zone that is highest in elevation and furthest from the compressor.
  4. Slowly open the compressor valve and keep the pressure below the maximum pressure specification for the lowest rated component.
  5. Work your way from furthest zone to the zone closest to the compressor and use two short cycles per zone rather than one long cycle.
  6. After blowing out the irrigation system, if your backflow device has ball valves, open and close your backflow device’s isolation valves multiple times.
  7. Leave the isolation valves halfway open and open the test cocks.

Do’s and Don’ts

It is very important to wear ANSI-approved eye protection when winterizing systems, as compressed air can cause serious eye injuries. Never stand over any irrigation components during the blow-out process.

When using an air compressor, never exceed 80 pounds per square inch (psi) when winterizing an irrigation system. Do not use compressed air on the backflow device. The rubber seals on a pressure vacuum breaker can melt from the heat of the air.

After the pipes have been blown out, avoid exposing the pipes to any more compressed air as it can cause friction and heat that can damage the system. Never run the compressor without at least one irrigation control valve open.

Choosing the right air compressor

Choosing the right air compressor is important because smaller ones will struggle to provide the proper pressure and volume needed to purge the system and larger ones will run the risk of pressurizing too quickly and damaging the system.

To calculate the right size, simply know the gallons per minute (GPM) that flows through each zone of the system. Divide GPM by 7.5 to determine the cubic feet per minute (CFM), according to the Colorado State University Extension.

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