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Sprinkler winterization is essential for irrigation systems in regions where cold winter weather is likely. Water expands when it freezes, and any water trapped in a sprinkler system will put stress on the plumbing. Without winterization, homeowners run the risk of cracked pipes and fittings. Rigid polyvinyl chloride (PVC) pipes are more vulnerable to the effects of frost and cold, but even the more flexible polyethylene plumbing can rupture if sprinkler winterization is not performed.
In regions where freezing is likely, sprinkler systems are installed with a planned method of winterizing. The three types of sprinkler winterization available are the the air compressor or “blowout” method, the manual drain method and the automatic drain method. When the preferred method of sprinkler winterization is unknown, the blowout method generally is recommended.
An air compressor is required for the blowout method of sprinkler winterization. Compressors are widely available from equipment rental yards. After the water supply is shut off, the compressor is connected to the sprinkler system mainline, usually by a quick coupler or hose bib. Air pressure should be built up slowly to about 50 pounds per square inch (345 kpascal). If the sprinkler heads don’t pop up, pressure should be increased gradually until they do, but pressure should not rise above 80 psi (550 kpascal). After the lines are dry, the air compressor should be switched off, but the isolation valves should be left open half way, and the test cocks should be left fully open.
Manual draining is perhaps the simplest method of winterizing. Shutting off the water supply and opening the manual drain valves clears the mainline. Next, the stop and waste valve or boiler drain needs to be opened to allow the remaining water to drain. Test cocks on the backflow will also need to be opened. After the system is cleared, the manual valves are closed again, and the sprinkler system is ready for winter.
Automatic draining is triggered by low water pressure, opening a valve when pressure inside the pipes drops to 10 psi (about 70 kpascal). Shutting off the water supply and activating the system pressure release will open the automatic valves and empty the mainline. As with manual draining, the stop and waste valve or boiler drain must be opened to release water trapped between the shutoff valve and the backflow device. Opening the test cocks will clear the backflow device.
Using the blowout method for sprinkler winterization is not recommended for amateurs. If the system is pressurized too quickly or the pressure is allowed to climb too high, the sprinklers can suffer severe damage. For the best results, this procedure should be carried out by a qualified, licensed professional.