The Tri-Cities, which includes the cities of Pasco, Kennewick and Richland require sprinkler systems to be winterized if the lines are buried less than 24 inches deep which is the frost line for this area. The following is the basic procedure for winterization:
Unplug your controller/timer.
Shut off the water at the main valve. This is the valve located between the water meter and the back-flow preventer valve, or whatever back-flow prevention device you may have. If you do not have a back-flow preventer, simply shut off the first valve after the water meter. After shutting off the main valve there should be a blowout point which would be in the form of a riser with a threaded cap. Sprinkler systems that use Kennewick Irrigation District (KID) water will usually have a filter connected directly to the main valve. In that case you would connect your air compressor line to the filter or to the riser. The next step would be to open 2 or 3 valves in the valve box if using a large 185 CFM air compressor. To open the valves turn the air screw on the top of the valve to the left about 1/2 a turn.
The final step is to turn on the air slowly, when you see the stream of water turn into mist then it’s time to move on to the next valve.