Blowing out sprinklers is where a professional will attach an air compressor to the system and literally “blow out” the water from the lines, pipes and other parts.
A professional knows how much volume and pressure to use when blowing out sprinklers, as many do-it-yourselfers typically use an insufficient volume of air and after having forced some water out, the air will ride over the top of the remaining water. This results in the remaining water draining into low spots and subjecting the system to freeze damage.