Sprinkler Winterization or “Blowouts”
There seems to be a lot of confusion regarding the proper methods for winterizing your residential underground sprinkler system. We aim to clear up this matter with information directly from the manufacturers themselves.
The Purpose of a “Blowout”
The main purpose of performing a “blowout” with compressed air is to purge your system of any remaining water so that once freezing temperatures are reached, the risk of any freeze related damage to any of your system components is minimized.
Misconceptions
One common misconception about “blowouts” is that you must get every last drop of water out of your system. However, this generally isn’t necessary as trace amounts of water are likely going to remain in some zones but it most likely will not be enough after freezing and expansion to cause any damage. Furthermore, excessive run time for each zone may cause damage.1-3
Another misconception is that you must have a very high PSI output from the compressor in order to purge all of the remaining water from your system. However, this is simply not true and may cause damage to your system.1-4
Best Practices and the Risks of not following them
First, let’s start with what we mean when we refer to PSI. This stands for pounds per square inch and it’s a measurement of pressure. Having enough pressure to move the water out of the system is important but so is having enough volume of air as well. We measure this volume of air in CFM or cubic feet per minute.
You’ll notice that when you look at your compressor it will give you a CFM figure at a given PSI. This is important to know because in order to move a large amount of water out of your sprinkler system in a reasonable amount of time, you’ll require a rather large CFM that most household compressors will not be able to meet.
Unfortunately, misconceptions are not limited to homeowners but also impact irrigation professionals as well. For example, many will use compressors with a PSI output of 120 or even greater. Some reason that if 60 PSI is sufficient then 120 PSI must be excellent. Such logic is unfortunately not only faulty but can cause damage to your system.1-4
While recommendations from manufacturers vary, they generally recommend that you provide a PSI no greater than the lowest rated component on a given zone. For most systems that have polyethylene-based lines, they recommend no more than 50 PSI and for those that are PVC-based, no more than 80 PSI.1, 2, 4 While it’s true that most polyethylene-based lines are rated for a PSI of at least 80 (and some up to 100 PSI for a 1 inch line), a more conservative approach seems wise. With respect to a minimum effective CFM, these figures vary with some suggesting that as little as 10-25 CFM would be effective while others suggest a minimum of at least 50 to 80 CFM. 1, 2, 4
Best Practice for Residential Sprinkler Winterization
A best practice in this case, based upon the available recommendations of manufacturers would be to utilize a PSI of no greater than 50 PSI while providing a CFM generally in the range of around 25 CFM at minimum and more ideally, around 50 to 80 and potentially as high as 125 CFM. 1, 2, 4 The larger the system, the greater capacity one will need. While a 50 PSI maximum is ideal, a maximum of up to 80 PSI or even 100 PSI may be possible, at least based upon the rating of the polyethylene-based lines used for the zones. However, we must keep in mind that as the pressure goes up, so does the risk of damage. Additionally, the technician visiting a home likely doesn't know the ratings of components that are underground.
These ideal PSI and CFM outputs are out of the reach for homeowners that have a standard compressor. Instead, the large compressors that require a trailer or some of the more expensive compact compressors will allow one to reach these figures.
Risk Associated with Using Excessive PSI
Some local irrigation professionals will regularly use a PSI exceeding 100 and even greater in some cases, presumably believing that this will provide a faster and more thorough blowout. However, not only is this not the case, it increases the risk of system damage to various components that were not designed to withstand such pressure.1-4 A more cynical interpretation might be that these irrigation professionals actually benefit by causing system component damage as this will allow for additional work to be done in the spring. While we can’t pretend to know the motivations of others in the irrigation profession, we can at least avoid their errors.
Recommendation: If your irrigation professional pulls up to perform your winterization, we recommend asking to see the gauge on their compressor to ensure that they are not using excessive pressure that could damage your system. If they insist that using a PSI greater than 50 (and certainly if they are using a PSI greater than 100) is not only “fine” but preferred, it may be time to consider a change.
References
1. Hunter Industries. Winterizing Your Irrigation System. Retrieved from: https://www.hunterindustries.com/sites/default/files/tech_Winterization.pdf
2. Rain Bird Corporation. Homeowner’s Guide to Winterization. Retrieved from: https://www.rainbird.com/sites/default/files/media/documents/2017-06/WinterizationGuide.pdf
3. White, P. Irrigation Winterization. Turf Magazine. Nov 1, 2009. Retrieved from: https://turfmagazine.com/maintenance/irrigation-winterization/
4. Weathermatic. Winterization (Blow Out) of Irrigation Systems. Retrieved from: https://support.weathermatic.com/hc/en-us/articles/202661660-Winterization-blow-out-of-irrigation-systems