As the machine is operated, the shag pad rotates on the carpet. This removes the soil as it is absorbed on the shag pad. The shag pad can also be moistened with detergent. When one side of the pad becomes soiled, the pad is reversed until both sides are soiled, at which time it is replaced. This system uses detergent in the form of a foam.
Machines are available that generate foam, which is agitated on the carpet by brushes.
The foam is then removed, with trapped soil, by an extraction-vacuum pickup. It is vacuumed off after about half an hour, removing the soil suspended by the compound. As explained earlier, vacuuming alone, although essential, cannot maintain the appearance of a carpet at an acceptable level for long. Depending on various factors, the appearance of any carpet will ultimately reach an unacceptable level. At that stage, cleaning is necessary by one of the methods mentioned above.