There are multiple methods to clean a carpet. In the professional arena there are two main types, hot water extraction and VLM (very low moisture). Each has its own role in professional carpet cleaning.
Let’s start with VLM, or commonly called dry cleaning. Dry cleaning was originally designed to be used as a commercial carpet maintenance tool to be used in between hot water extractions. It has made its way in to the residential cleaning as a quick and inexpensive way to improve the carpets appearance. One way to dry clean a carpet is by what is called the Host method. This process involves a cleaner spreading a powder on your carpet that is mainly composed of ground up corn. After that is spread evenly a brush machine will grind the particles against the carpet fibers to remove soil. Once the soil is separated from the fiber with the brush machine the vacuuming process would take place. The technician would then vacuum out the corn particles out with a standard, upright vacuum and hopefully bringing the soil out with it. I Have been to homes that were previously cleaned with the Host method and filled my vacuum with Host corn granules during my pre-vacuum phase of carpet cleaning.
Another way to dry clean is by using the VLM method or very little moisture. A thorough vacuuming should be done prior to wetting the carpet. A technician would apply a small amount of a cleaning agent labeled as an encapsulant. This solution is then agitated into the fibers with a floor scrubber. Floor scrubbers come in the form of 175 rpm floor machines, oscillating machines, and counter rotating brush machines. Each are different in their forms of agitation, but all have the same job in mind- suspend soil. When you are agitating the fibers coated in the encapsulant you are breaking the soil off the fiber and suspending that soil in the encapsulation solution. The extraction of these soils happens in two ways. One is by the absorbent pad under some floor machines soaking up the moisture and soil. The second happens the next day or a few hours later after the carpet is dry and the encapsulation solution as crystalized on the fibers. A household vacuum is run over the cleaning area. The vacuum breaks apart the dried encapsulant off the fibers and sucks up the crystalized soils.
Hot water extraction, commonly referred to as steam cleaning, is the next cleaning process of discussion. Hot water extraction uses a vacuum and water pump system to rinse and extract soils from your carpet. A technician would first vacuum the carpet with a standard upright vacuum cleaner to remove most of the dry soils. Then a detergent should then be applied to loosen the soils off the fibers. Applying the detergent is usually performed with a pump-up sprayer or an inline injection type sprayer to the detergents dilution guidelines. There are many various detergents on the market that are designed to treat a general traffic and spots. There are even more that treat specialty soiling conditions. Deciding which to use takes research and experience in the cleaning industry.
Once the detergent is put down one can agitate the fibers with various pieces of equipment like the scrubbing equipment used for dry cleaning. One of the most common scrubbing tools is a 175rpm floor buffer with a pad or brush depending upon the carpet type and soil level. An oscillating scrubber works in about the same way as a 175 buffer but easier to control and can use the same pads or brushes. A counter rotating brush machine has rotating nylon brushes that agitate the carpet. There are other forms of agitation but they all work toward the same principal of suspending soils in to the detergent.
Once the detergent it agitated to put the soil in to solution it is now time to hot water extract the fibers to rinse away detergent and soiling residues. Steam cleaning units are machines using a vacuum to lift the moisture off your carpet and a pump to rinse. These vacuums and water pumps can be powered in two main ways. The first is referred to as a potable hot water extraction unit. These are electric powered and are usually brought inside to the area being extracted. The second way is a fossil fuel powered cleaning unit which is mounted outside in a van or trailer. The cleaning units run on fossil fuels as generally called truck mounts units. These truck mounts turn their vacuum and water pumps with either a small engine or are PTO shaft driven using the vans motor. Heated water speeds up water molecules and cleans better than cold water. Heat is made through electric, propane, diesel, coolant, and exhaust powered heat exchangers. These cleaning units will have a high-pressure water hose and vacuum hose the connect the unit to what is called a carpet wand. The carpet wand has a vacuum chamber and water jets attached to the head of the tool. The technician will push the wand across the surface of the fibers to rinse and extract. Knowing the proper amount of rinsing and extracting takes experience from the technician. Carpets, if properly extracted, will dry in around 4-6 hours.
Hopefully you have come out with a better understanding of the two most popular carpet cleaning methods, hot water extraction and Very Low Moisture.