Hot Water Extraction
Though commonly called "steam cleaning", no actual steam is involved in the HWE cleaning process apart from steam that may escape incidentally from hot water. When the cleaning solution comes in contact with the carpet, it is 122 to 248 degrees Fahrenheit, depending on the heat available from the cleaning unit. In a modern truck-mounted carpet cleaning machine, water can be heated under pressure to over 302 degrees Fahrenheit, but after passing through high-pressure steel braided hoses and several manifolds, the water loses much of its heat.
HWE begins with preconditioning using a pre-spray cleaner (typically neutral or alkaline) being applied to the soiled surface, followed by light agitation with a grooming or pile brush. For heavily soiled areas a Counter-Rotating Brush (CRB) can be used after the appropriate dwell time. Next, the surface is passed over several times with a cleaning wand or rotary extractor to thoroughly rinse out the preconditioner, using an acidic solution to reduce the pH of the carpet fibers back to a neutral state. In the next stage, the carpet is dried using a fan or carpet dryer. The final stage is resetting the carpet pile to remove any unsightly wand lines, commonly referred to as "shark teeth", with a carpet groom or brush. (wikipedia)