Proper winterization will extend the useful life of the irrigation system, but the type of winterizing you need to complete depends on the local climate.
In temperate climates the soil doesn’t freeze, but occasional cold spells bring on freezing conditions. Winterizing protects any parts of the system that could freeze under such circumstances – parts such as backflow devices, pumps that are not in a heated environment, and sprinklers that are on risers.
To prevent water that is contained in these components from freezing and causing damage, insulate or drain any parts that are above ground. Additionally, pumps and controllers should be turned off if the water is temporarily turned off.
In colder climates the soil freezes, and the frost line is often deeper than the burial depth of the irrigation pipes, so you’ll need to use other procedures to winterize the system. Some old systems may have drains located at low points in the pipes, in which case gravity will drain most of the system components. However, not all of the water will drain completely from closed-case rotors or the valves.
If the system was designed and installed to drain by gravity, locate the drain valves and open them. A valve near the point of connection will also need to be opened to allow air to enter the system. This helps move water to the drain valves located at the low points. Unfortunately, this step will not move water that is in low points or dips in the piping; these sections are susceptible to freeze damage.
An air compressor can be used to move the trapped water. The key to success with this method is delivering a large volume of air at a relatively low pressure. To successfully winterize the irrigation system with compressed air, follow these steps:
1. Choose the size of the compressor based on the size of the irrigation system. Typically, you will need 200 to 300 cubic feet per minute (CFM) to create an adequate volume of air to push the water out of the pipe and through the sprinklers for large systems such as golf courses, sports field complexes or large parks. The amount of air pressure should be around 40 to 50 PSI. It should never exceed the pressure rating of either the pipe or the system components, and it should never exceed 80 PSI.
2. Consider the temperature of the compressed air. Many trailer-mounted air compressors that create the volume of air necessary will blow hot air. It’s preferable to find an air compressor that blows cold air, but if you can’t, you can cool down the air. To do this, take several hundred feet of air compressor hose and stretch it out on the ground so the heat will dissipate. This will help avoid softening or melting the plastic pipe and fittings where the compressed air enters into the irrigation system.
3. Get the proper safety gear. This process is potentially very dangerous, so make sure the personnel doing the work has the proper personal safety equipment, such as goggles, ear protection, gloves, etc., to do the job safely.
4. Turn off the water supply and deactivate the pump station if there is one.
5. Manually open at least one zone valve. This ensures that the compressed air will always have a place to push water or escape out of the piping. This is usually the zone farthest from the air connection.
6. Attach the compressor hose to the irrigation mainline using the proper fittings and adapters. You can do this by using a quick coupler location downstream of any backflow device or pump, or by using a specific fitting that has been installed to facilitate winterization.
7. Set the pressure-regulating valve on the compressor to 50 psi.
8. Activate the station valve at the controller or manually open the valve to be winterized.
9. Gradually open the compressor valve and increase the flow of air until the sprinkler heads pop up. The amount of air you use depends on the size of pipe, the length of the pipe run, and the number of sprinklers on the line.
10. Run the air until the water is evacuated from the sprinklers, and the last sprinkler on the lateral line is blowing air. Blowing air through sprinklers that don’t have any water for an extended time may cause damage, so be sure to move to the next station when there isn’t any water being dispersed. This usually occurs within approximately two minutes at each station.
11. Move to the next station on the controller, taking care that there is always a valve open somewhere to avoid building up excessive pressure in the system.
12. Sequentially activate (either at the controller or at the valve) each station. This allows air to move all of the water through the sprinklers.
13. Repeat the process in steps 10 through 12 until all stations have been winterized with compressed air. Keep in mind that you’ll only need to activate the valves a short time to verify that all of the water has been evacuated from each sprinkler zone.
14. Turn off the compressor. This allows any air in the compressor storage tank and in the piping system to disperse before trying to disconnect the compressor hose.
15. Remove the air compressor hose, fittings and adapters from the sprinkler mainline.
16. Put the controller in the off position. If you disconnect it from the power source, any programs may be lost. It is recommended that the common wire(s) be disconnected from the controller to prevent any accidental signals from being sent to pump station relays, etc.
17. Follow best practices to remove any water from the backflow device chambers and valves or from the pump housing. This is recommended even in heated pump houses in case of a power outage and/or freezing conditions.
On extremely large systems, it may work best to use isolation valves and work on one section of the system at a time. Avoid using compressors that are too small to generate the volume of air needed to push the water out of the system. Smaller compressors will increase the amount of time spent completing the job and will often lead to surging, which occurs when you fill the compressor tank and then quickly open the valve so that a surge of air rushes into the system. This can cause broken fittings or shattered pipes that will need to be fixed prior to spring start-up.
If you follow these steps, you can rest assured that you have properly winterized your system.