Grounds Management

Don’t Forget to Winterize Your Irrigation System

Property owners want to maintain a pleasant landscape for a host of reasons, such as attracting quality tenants or to portray themselves as a positive force for their community, among other reasons. Whether the landscape is beautifully ornamented or a simple, lightly planted green space, facility managers charged with maintenance and operations have come to rely on automatic irrigation systems to help keep everything growing and green. While these systems typically function in a “set it and forget it” fashion, they do require winterization ahead of the cold weather.

Low angle sprinklers in action.

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The reason for this is simple: Any water left in the system will begin to freeze as the temperature drops. Water will expand as it freezes, which can cause significant damage to the pipes, sprinkler heads, and/or sensors, leading to significant and costly repairs.

There are two options for winterizing your system:

  1. Get a professional to take care of it for you; or
  2. Do it yourself.

Let’s examine both options a little.

Hiring a Professional

For most, this is the easier option, as it requires nothing more than a phone call or two and writing a check to cover the cost. While the average homeowner will spend less than $150 to have a professional winterize his or her system, the cost to service a commercial system will likely exceed that. If you do not have a landscaper or specialist you are working with, ask around for recommendations, or get quotes (and references) from companies in your area.

Do-It-Yourself Winterizing

If you are looking to save a few dollars and have the time to tackle the project, you could always service the system yourself. However, you should understand that there are some potential risks in doing so. You would also need to purchase or rent an appropriately sized air compressor to get the job done.

While it is possible to let gravity do the work for systems with either manual or automatic valves, it’s not always recommended. These systems function on two basic assumptions: that the system was properly installed and graded and that the pipes have not shifted over time. Given that the ground expands and contracts with the temperature, there’s no way to know whether everything is stable without digging up the system. With that, the folks at the Colorado State University (CSU) Extension recommend blowing out all systems (manual, automatic, and electronic valve systems) just to be sure.

Choosing an Air Compressor

It’s always best to pick the right tool for the job, and choosing the right-sized air compressor for winterizing your irrigation system is no exception. A compressor that puts out too much air is as equally problematic as one that puts out too little. So, you need to make sure that your compressor is putting out the proper volume of air in addition to an appropriate pressure. For example, if you have good air pressure but low air volume, you’ll wind up forcing some of the water out of the pipes, with the air traveling over any remaining water in the system.

Pressure Gauge

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There are two factors to account for when selecting your compressor: pipe material and the system’s gallons per minute (GPM). The ideal air pressures range between 40 and 80 pounds per square inch (psi); how much pressure you use directly depends on the pipe material. If your system uses a flexible black polyethylene pipe, you’ll need to stay under 50 psi; you’ll need to stay below 80 psi if you’re using rigid PVC pipe. The CSU Extension suggests that if the sprinkler heads stay aboveground after the water is blown out, with compressed air still flowing through the system, you’re using the right compressor for the job.

Using a compressor that is too large for the job can have detrimental results, so it’s important to do some quick math to determine the best size for your system. To figure that out, you’ll first need to know how many GPM your system is designed to handle. This information should be noted for each zone on the irrigation plan, or you can add up the GPM rating for each sprinkler head in a zone to come up with a quick estimate.

Once you have that number, divide the total GPM for each zone by 7.5 to get the number of cubic feet of air per minute (CFM) required. That number will be the psi needed to blow out the system (GPM/7.5 = CFM). Here’s an example from the folks at the CSU Extension:

“If the system is designed for 30 psi and 20 gallons per minute per zone, divide 20 by 7.5. The answer is 2.66 cubic feet per minute. A compressor capable of providing 2.66 cfm (cubic feet per minute) at 30 psi (pounds per square inch) will be required.”

Tomorrow, we’ll walk through the process of blowing out your irrigation system.