The Rotary Shampoo method uses an ordinary rotary floor machine (the same kind used for stripping wax), sprays shampoo onto the carpet from a dispensing tank and a rotary brush whips the detergent to a foam. Most carpet mills and carpet fiber producers discourage the use of rotary brushes on carpet because of the potential damage that can occur. Overwetting is common with this method which can cause jute straining, shrinkage and odor.
Shampoo methods are inferior due to poor cleaning plus resoiling problems. The Rotary Shampoo method can damage the carpet, especially cut pile (which is what most residential carpet is).