This is the restorative method of cleaning or “deep cleaning” of carpet and what most people think of when they think of carpet cleaning.
Basically you completely saturate the carpet and pad with water (and usually detergent or solvent carpet cleaning chemicals) to get chemical in contact with ALL soil anywhere in the carpet, emulsify it and vacuum or “extract” it.
Dry methods generally only get surface and near surface soil – not the stuff deep down in the backing and pad.
It is critical that the extractor be properly maintained and / or multiple extractions be done to make sure you get (almost) all the water out of the carpet. Leaving too much water in the carpet will rot it, delaminate it from it’s backing, loosen the glue that holds it to the floor, stretch it , lead to mold, and all sorts of other bad things.
Do not leave the job until the carpet is dry enough to finish drying completely in a couple more hours.
If you have used a “Green Machine” from late nite infomercials you have used carpet cleaning equipment similar to most self contained extractors. They also put water and detergent down with a spray nozzle, agitate with a brush and vacuum up with a vacuum attached to the other end of the machine.
Commercial machines go from sizes similar to a “Green Machine” all the way up to self propelled units about the size of a small asian automobile – machines that can clean 15,000 feet per hour versus a few hundred for the “Green Machine” and a thousand or so per hour for a small commercial unit.
There are also options to do all three operations separately with heavier duty single purpose equipment – a good choice for extremely heavily soiled areas – similar to my reference to using a bonnet cleaning in addition to normal extraction.
Finally the alpha equipment is called a truck mount unit. Usually instead of chemical these use heat and are sometimes called “steam cleaning”. Same result – heat is as effective, properly used as chemical at loosening and removing soil adhering to carpet fibers.
(It’s not steam however – even when it leaves the heater it isn’t steam, and when it gets to the end of the hose it’s a long ways below F212/C100 – but it’s still plenty hot enough to do the job, and to burn you – be careful. The suction hose used to extract water thru 300 feet of hose has one heck of a lot of suction too – you do not want to get your shirt, hand, etc anywhere near the intake – if you don’t want to lose your shirt, hand, etc)