Winterizing a Sprinkler System
You can pay the irrigation company $125 every year to blow out your sprinkler system, or you can use your air compressor and do it yourself. You just have to be careful not to leave any water in the line or it might freeze over the winter and burst a pipe. Also be aware that even the largest home compressor isn't powerful enough to blow out the entire system at once, so you'll probably have to blow it out zone by zone.
If you're into number crunching and you have the original irrigation layout showing the gallons per minute (gpm) of each sprinkler head, just divide the total gpm of each zone by 7.5. That'll give you the cubic feet per minute (cfm) your compressor needs to blow out the zone. Otherwise, just rent a 10-cfm compressor and hose from your local tool rental center.
Set the compressor air pressure regulator to a maximum of 80 psi for rigid PVC pipe systems, or 50 psi for flexible black polyethylene pipe. Then turn off the water supply and set the system timer to open just one zone. Next, open the manual drain valve at the end of that zone (if equipped).
Close off both valves on the backflow preventer. Then remove the plug on the blow-out port and screw in a quick-connect hose adapter. Snap on the air hose and connect the other end to the compressor (see photo). Then blow out the line. The heads should pop up and spit out water. Disconnect the hose as soon as they run dry.
Don't overdo the blow-out—without water cooling the plastic gears, they can melt in less than a minute. So move on to the next zone and allow the heads to cool. Then go back and blow out each zone a second time.