Yea....anything really over 80 your messin with...some guys have huge trailored compressors, which allows for them to winterize the entire system at once and under 3 minutes...ive seen this done...its pretty neat....its ok to winterize through backflow......like bhungue said water flows through..and if they are outside you have to get the water out
Thanks
Ray
Rays Above and Beyond Automatic Lawn Sprinklers