Everybody has their own way of carpet cleaning.  Being in the business for over 20 years i have seen almost every conceivable way there is to clean a carpet. Some ways you wouldn't believe, some ways are better than others.  Below are the three main ways of cleaning carpets.

Extraction: A carpet extractor uses a cleaning solution that is forced into the carpet by a pump then the solution is sucked out of the carpet with high power vacuum motors.  Pumps range in power.  Vacuum motors range from 135 cfm to over 200 cfm.  Heaters can be added to the machines either internally or externally.  Heated water tends to break up greasy dirt faster.  Good chemicals, see carpet cleaning chemicals for information, will do the work for you. Extraction leaves the carpet wetter than other systems, but it cleans deeper.  Portable and truck mount extractors have a base unit and a hose and wand.   If the carpet is cleaned properly it shouldn't take more than 4 hours to dry.

Same principle as a extractor but does not use a hose and wand and has a built in brush that scrubs the carpet between putting the solution down and vacuuming it up. This system is great for large commercial areas.

Extraction restoration: The proper way of deep cleaning a carpet. This is a two step program designed to deep clean the carpet.  1) prespray carpet with a good presprayor use a non-residue shampoo in a shampoo tank.   Agitate carpet with a rotary floor buffer with a carpet brush attached.  This loosens up the dirt that is on the top and deep in the carpet.  Let the chemical sit for a few minutes to actually break up the dirt after you scrub.  2) extract the carpet with a good extraction cleaner (like the chemspec 90) or use a rinsing agent (like textile rinse from chemspec or rinse out from cello).  The rinsing aid will flush out all chemicals and dirt from step 1 and from previous cleanings.

Bonnet cleaning: Bonnets are made of synthetic, natural or a combination of both materials.  Bonnets are round pads that go under standard speed floor buffers. The bonnets use friction to pull dirt from the top of the carpet fibers. This is a good system when cleaning a carpet frequently, when the carpet needs to be dry shortly after cleaning or when a browning problem occurs. However, this is not a deep cleaning method. It is recommended that the carpet be sprayed with the detergent then buffed with a dry bonnet, when the bonnet gets dirty flip it over or use another one.

Rotary brush or dry foam: Uses a foaming shampoo that may dry to a light powder or crystal. The shampoo is applied with a brush and a standard speed floor buffer  machine, the brush generates foam as it spins or a specialized machine that generates foam before getting agitated with a brush. This system is likely to leave the carpet with a sticky residue if not used properly.

Encapsulation: Encapsulation has been around for 30 years.  Since the first carpet shampoos that dried to a crystal or powder.  You would have to vacuum after the solution dries.  With the invention of certain chemicals encapsulation has come a long way.  Their are many different formulas that different manufacturers use.  The different formulas work differently.