The Importance of Agitation
"Agitation in some form is fundamental to accomplish uniform chemical penetration and distribution. Without this important step, soil suspension is superficial and non-uniform , perhaps even in resulting in soil streaks following extraction.
Primarily there are two phases in which aggitation is employed in the soil suspension process. First, hand brush agitation using a multi-bristled brush or comb to work in pre-conditioners is an effective and time-efficient, although less aggressive, technique for applying agitation. Brush agitation refers to the fore-and-aft stroking of pre-conditioned carpet pile throughout traffic areas, placing particular emphasis on entry, pivot, and heavily soiled areas. Second, mechanical agitation involves the use of mechanized rotary or cylindrical, nylon-bristled brush action to achieve aggressive agitation and distribution of pre-conditioning chemicals into the carpet pile for maximum soil suspension."
Jeff Bishop
The Science of Carpet Cleaning, 2003