This is not intended to beat up on one or the other. This is just an opportunity to look at the benefits of both processes. Just as one person may want to drink whole milk, someone else may want 1%. The consumer is very capable of take the information and decide what is best for them, and their particular circumstances. It may be that dry cleaning is needed one time and steam cleaning is needed another time.
Steam cleaning carpets have many different processes. It is done mostly by using a machine that allows the technician to spray a liquid and also extract the liquid through a vacuum. There are small portable machines to large truck mounted equipment. With either type of system the soap can be applied to the areas to be cleaned first and then the equipment can spray out clean water to rinse out the soap and dirt. In most cases soapy water is sprayed out of the equipment at a high pressure and then extracted out with the vacuum. This will dislodge dirt from the surface and then it is sucked out and into a holding tank. This process will leave a soapy residue on the cleaned areas. When the soap is pre-sprayed on the carpet, clean water can then be sprayed from the equipment at a high pressure to dislodge the dirt, at the same time rinsing the soap out, so you have no residue.
Dry cleaning is a process that requires a product to be applied to the surface to be cleaned (carpet or upholstery). It can be one of many things. In general, it is usually a soap, or a protector that is applied. A clean bonnet is then used on a buffer, or on upholstery with a towel by hand, and run over those areas. The bonnet is used until it is as dirty as the area being cleaned. Then the bonnet is turned over and run over the area again. When that is equally dirty, another bonnet is used. This process is repeated as many times as it is needed to complete the acceptable appearance. After the areas have been cleaned a nap brush or carpet rack is used to take out any "buffed look" the bonnet may have left behind.
When soap is used it will have a better affect on cleaning the area. Soap is made to attract dirt, so in areas that have ground in dirt, it will be able to break down the dirt and have it bond on to the bonnet. Because the soap is not rinsed out through the dry cleaning process, it will remain. It will continue to attract dirt. Even though you can't feel it, even though it will be dry, it is sticky. A protector on the other hand may not be able to clean the carpets as effectively, but it is engineered to be left on the areas after cleanings. It helps repel dirt from becoming ground into the cleaned areas quickly. One of the greatest benefits of having you carpets or upholstery dry cleaned is that the areas dry quicker than steam cleaning. The chances of harming you carpet from over saturating is not very likely. If your having company over to your home tonight and you need it cleaned and dried in a hurry, dry cleaning maybe the way to go.
Portable equipment can be taken right to the areas to be worked on. The hoses are short. They have a cleaning solution tank and a waste tank. Some have a solution tank, that have warmers, to keep the solution or water warm. This is important, because the hotter the water the more effective the cleaning will be. The water that is used usually comes out of the hot water heater at the location the cleaning is taking place, so the water starts at that temperature and then as the cleaning takes place the water will stay as warm, or become cooler while staying in the tank until it is used. Most hot water heaters are set around 120 degrees. By the time the last bit of water is used it has become much cooler than that. The blower, or vacuum on the portable unit is much smaller than the truck mounted equipment. In some situations only a portable unit can be used because of the distance from a truck mount.
Although the truck is not in the room that is being cleaned, it has a lot that compensates for that. With the truck mount you get the hottest water in most cases. The water is taken from an outside faucet and heated in the machine. In the St. George Utah area you can run water at about 180 degrees continuously, and in the summer even hotter. The blower may at times be 100 feet from the working area, but 2" hoses are used to keep the suction from depleting, and the blowers in some cases are larger than some portable units, producing a great deal of extraction power. The solution or water pressure can be regulated as needed for distance also. With this system a door or window is always left open to allow the hoses to connect the working area to the machine outside. It may take longer to dry, but you can clean up a lot more with steam cleaning then you can with dry cleaning. Just like if you were to wipe off you hands. It does a good job, but you can feel how much cleaner your hands feel when you wash them with soap and rinse them with water.