There are several things that must be done to winterize a sprinkler system. The first step is to determine if the system uses auto-drain valves. If Auto-drain valves are present, then all you need to do is turn the main water supply off, and then loosen the solenoid on each valve to let air inside. The water should flow down hill and out of each zone through the auto drain valve. You may have a manual drain for the main line between the shut-off valve and the valve manifolds. If a valve is present open it to allow all water to drain.
If you system does not use auto-drain valves, then an air compressor must be used to blow the water out of the zones. Turn off the main water supply to the sprinkler system, and hook up an air compressor to the system. Pressurize the tank to about 60 psi and then open on of the valves manually. Run that station for 2 to 3 minutes to allow all the water to be removed from the system. Shut that valve off and pressurize the tank again. Repeat for the next zone. After all zones are empty, loosen the solenoids to allow air to enter the top of the valve.
This is a general guideline for winterizing a system. You system may require additional steps depending on the particular installation. There are services available in the Yellow Pages to perform this task for you. Please look under Sprinkler Installation if you need someone else to do the work.
Note: Air Compressors will also need an air flow rate between 4 and 8 cubic feet per minute.
View Winterizing Video