@jsurpless, to blow out sprinklers properly, the volume of air the compressor puts out is more important than the size of the compressor. In short, air volume should be high and air pressure low. This combination of high volume and low pressure will minimize the damage that can occur during the winterization process. It is very important to select the right air compressor for the job. Some small shop compressors (2 hp) may not be adequate to complete the winterization procedure properly.
You'll want to use an air compressor with a Cubic Foot per Minute (CFM) rating of 80-100 for any mainline of 2" or less. These types of compressors can be rented at your local equipment rental store. The blow out pressure should remain below the maximum operating pressure specification of the lowest pressure rated component on that zone and should not exceed 50 pounds per square inch (psi) for poly pipe system or 80 psi for PVC pipe systems. Also, it's not advised to run the compressor without at least one sprinkler control valve open.
Hope this helps