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Winterization Overview – Preparing Your Irrigation System For Freeze

Tuesday, October 27, 2020
By Rod McWhirter – Rain Bird Corporation
Question on how to winterize your irrigation equipment? Contact Brian Freeman at for more information.

With a little over three months before cold weather sets in up north, it’s time to start thinking and planning for winterization of your irrigation system. It is obvious that winterization is necessary in those areas that experience deep freezes, but consideration should be given to some level of preparation even in areas that have freezing at shallow depths of soil or even just at the surface.

It is a well known fact that water expands as it changes from liquid to solid at 32 degrees F. What is not as well known is how much it expands… almost ten percent! This means that as temperatures drop below the freezing point, ten cubic feet of water converts to eleven cubic feet of ice!

If this occurs in a rigid, closed vessel that is full, such as a length of PVC pipe in an irrigation system, a sprinkler head full of water, or a steel pump discharge line that is full, damage is inevitable. And often the damage is severe. More bad news is that the damage done by freezing water may not be evident until the following season when the system is returned to normal operation. Even then, the damage done by this expansion of freezing water is not always recognized as such, and much time and money can be wasted troubleshooting other possible causes of the damage.

This article will give basic guidelines for winterizing a golf course irrigation system. Irrigation systems vary, so be sure to take into consideration the unique setup on your course.

While the most important function in winterizing, especially in the deep freeze climates, is the purging of water from the piping system, care must also be taken to prepare pump stations, sprinkler heads, quick coupling valves, and even above ground components, like satellite controllers, weather stations, rain buckets and sensors, etc.


Again, this is the single most important function of winterization. It is also the most time consuming, and in some cases the most misunderstood.

In order to systematically purge the water from a piping network as extensive as that of a golf course irrigation system, it is very helpful if you have an accurate record drawing (as-built) of what lies underground. The important components that need to be indicated on such a drawing are sprinkler heads, pipe and pipe sizes, isolation valves, manual and automatic drain valves, air relief valves, and quick coupling valves. Although it is intuitive that air relief valves and drain valves are at high and low elevation points respectively, not all high/low points have such a valve, therefore it is also helpful if the record drawing shows elevations throughout the course.


Obviously, the first order of business is to shut down the pump station and close pump discharge isolation valves. Prior to opening drain valves, assure that sumps or other drainways are clear, and that the drain valves are in working order. To prevent vacuum formation, the pipe system being drained must be vented to atmosphere, which can be accomplished in various ways… just assure that the opening(s) for venting cannot allow debris to enter the pipe. Opening a few quick coupling valves at the higher elevations can be of help in venting. Opening quick couplers at low areas can assist in the drainage. 
Once gravity drainage is complete, close all manual drain valves and quick couplers.


Upon completion of system-wide drainage, it may be necessary to complete the process of purging water from the lines, especially in the deep freeze climate areas. This is because not every low spot in the piping system has a drain valve, and the “leftover” water collects in these areas, potentially filling some of the pipe, fittings, and other components. If full of water, these components are then subject to freeze damage.

Another reason for compressed air blow-out is to drive water out of the cases of valve-in- head sprinklers. V-I-H sprinklers have a chamber of water in the case above the valve, as well as in the drive mechanism of the internal assembly, and in the solenoid actuator. Water must be expelled from these areas, and compressed air can be an effective method, IF DONE PROPERLY.

• AIR VOLUME is what moves the water out of the pipe.

• AIR PRESSURE, while necessary to force the air through the pipe, should NOT EXCEED 60psi. Adequate air pressure is 40-50psi.

• HEAT is a potential hazard in compressed air blow-out, especially in plastic pipe. Compressing air causes it to heat up drastically and care must be taken to avoid introducing this overheated air into the system. This is usually accomplished using a given length of metal pipe such as a heat sink (approximately 3-5 feet) between the compressor discharge and the plastic mainline pipe. Some compressors are equipped with a heat dissipation device called an ‘aftercooler’. The compressor instructions, or the company providing the machine or the service should have detailed information about how to avoid this hazard.

• DANGER is another potential hazard when using large air compressors. Only an experienced person should operate a compressor, and it is imperative that the machine be in good mechanical condition and have all safety components operational, such as pressure regulators, gauges, relief valves, and pressure switches. Never leave an air compressor unattended while it is running.

Compressed air blow-out of a pipe network is successfully accomplished when done systematically with the above mentioned record drawing and a plan for isolating different areas of the course. In most cases it is not practical to try to blow out an entire irrigation system from one location. This is especially true if there are lots of elevation changes throughout the golf course. In general, the pipe network needs to be divided into sub- areas, isolated from the rest of the system, then purged, and finally isolated one last time.

Once a sub-area is isolated, the compressor is connected at the highest point, typically via a 1 ½”- 2” connection. Valves and sprinkler heads at the far end are opened first. As water is purged from each zone, that zone is closed or isolated, and more zones are opened in the direction of the compressor. Many veterans of winterization make it a standard practice to repeat this process the following day to make sure they have driven as much water as possible out of the low spots.

As for compressor size and capacity, here are some parameters:

- If you plan to use the automatic control system to open and close valve-in-head sprinklers during blow-out, it is imperative that you not exceed the system’s flow capacities in doing so. To size the compressor accordingly (or set the regulator appropriately), divide the normal system water flow capacity by 7.5 to get the equivalent volume of air (CFM) needed to move an equivalent volume of water at approximately the same velocity.

- Example: A 2,000 gpm system would need a compressor with approximately 250-300 CFM capacity at 40-50psi. Actually, if the irrigation system pipe network is sub-divided into several smaller areas for blow-out purposes, an even smaller compressor should be adequate. Remember, haste is not important here, and trying to blow out a large pipe system in a short amount of time using a high capacity and/or high pressure compressor is asking for trouble. You just might do more damage to the system components than the freeze you are trying to protect against!!

A Note about Compressor Specifications … Air compressor performance is specified as cubic feet per minute (CFM) at a given pressure (PSI). Just as in a water pump specification, this is an important parameter when knowing what size compressor to use for your system.


Compressed Air Blow-Out Summary

• Drain as much water as possible from the lines first.
• Use a properly sized compressor. It is NOT advisable to blow-out the entire system at once or from one location.
• DO NOT allow a compressor to exceed 60psi!!
• DO NOT introduce over heated air into the piping system.
• DO NOT force more water through the pipe system than you would with a normal irrigation cycle.
• Take your time! Trying to do this too fast can result in damage to all components.
• Take your time! Trying to do this too fast can be unsafe.


If your field satellite controllers are of the normally open hydraulic type, the hydraulic actuators or modules must be drained. Likewise the supply lines and hydraulic tubing going to the sprinkler heads must be drained and blown-out. Most of the controllers sold in the last 7-8 years are solid state and modular in design, making it easier than ever to unplug and remove the panel assemblies (face plates) from case or pedestal. With either these or the older style electro-mechanical units, if you are in the extreme cold climates you should consider unplugging the panel assemblies and storing them in the shop for the winter.


The manufacturer of your pump station should have detailed instructions on the proper procedure for winterizing or otherwise protecting your station and any related equipment or components.

Anything containing water that is above ground or outside that will be exposed to freezing temperatures must be drained, insulated, or otherwise protected. Don’t forget things like copper/brass tubing on control valves (Clay Valves), pilot valves, backflow preventers, pressure regulators, etc. All tanks and pipelines connecting them need to be drained.


If you have an on-site weather station that interfaces with your irrigation system, you will need to drain the rainwater collection and sensing device(s), and prevent water from entering them throughout the winter. It is also advisable to cover or remove the other sensors for the duration of winter. Soil moisture sensors should be disconnected and taken out of the ground.

With patience and diligence, a good record drawing of all underground components, and a properly sized and operated air compressor, your irrigation system can be safely winterized and protected for the duration of a severe winter.

Question on how to winterize your irrigation equipment? Contact Brian Freeman at for more information.

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