Fan or Impeller Types & Performance

The fan or impeller is the disk shaped structure with fins that creates the actual suction in a vacuum cleaner. It is always placed directly onto the shaft of the Suction Motor so that it spins at a very high speed. Suction is created by the effects of centrifugal force acting upon the spinning air within the fan. As the fan rotates, the spinning air moves outward away from the hub, creating a partial vacuum which causes more air to flow into the fan. The fan is often considered an integral part of the suction motor since it, the fan housings and the motor are assembled as a unit by the manufacturer. Traditionally, the more powerful suction motors contain two or three fan stages pulling in series. A "stationary fan" located between the fans removes the spin from the air exiting the first fan and directs it inward toward the hub of the next fan. However, some newer motor designs, like the Miele Vortex Motor used in their vacuums, incorporate one specially designed fan to produce as much or more suction than a traditional two fan motor. The fins of the fan in this newer design are much wider near the hub to enable more air to be spun by them. They typically have more fins than their traditional counterparts as well.

There are two basic vacuum cleaner fan designs. The first type is used in the traditional upright and some hand held vacuum cleaner designs while the other type is used in all other designs including the "clean-air" upright, two-motor upright, two-motor power team, standard canister and central vacuum system.

The traditional upright design is often referred to as the dirty-air design or direct air design since the air goes directly through the fan while still carrying the dirt which was picked up. In order to withstand the impact of the dirt on its fins, the fan is one molded piece consisting of a thick disk with heavy curved fins. This type of fan does not have two parallel disks like the clean-air fan does. Traditionally, this fan has been larger in diameter with wider fins than its clean-air relative. Therefore it is capable of handling a lot of air-flow in systems having rather low internal resistance, even when driven at a relatively low speed. At these lower speeds, the suction created is considerably less than its clean-air counterpart and generally not very effective in systems which include a hose and attachments. Later uprights using this design have much more power and spin the fan at speeds closer to that of the clean-air system fan. This produces much improved performance, especially when using attachments. Our experience has shown that, on upright cleaners with the dirty-air design and motors drawing about nine or more amperes (amps) of current, the higher speed of the fans causes a much higher failure rate. At that speed, when a vacuum cleaner is run with a broken fan for even a relatively short time, the bearings and often the motor are damaged extensively. Some exceptions to these fan breakage problems are cleaners like the Kirby uprights and the Heavy Duty and Commercial Sanitaire uprights by Electrolux Home Care Products North America (formerly The Eureka Company) which use slower large diameter fans. Although typically less durable, dirty-air designs often are capable of producing more air flow for better carpet cleaning while clean-air types usually produce more suction for improved performance with a long hose and attachments.

The fan for the clean-air design looks a lot less rugged than its dirty-air cousin. It consists of two parallel disks with curved fins mounted between them. The one disk has a very small hole at its hub for mounting it on the motor shaft while the other has a hole about one and one-half inches in diameter in the center where the air enters it. Typical dimensions are six inches in diameter with one-fourth or three-eighths inch wide fins. It spins at a very high speed, creating stronger suction than its cousin but is more limited in the amount of air-flow it can handle efficiently. Since the air is cleaned by most of the filtration system before it goes through the fan, the risk of failure of the fan is greatly reduced. Clean-air systems generally have better performance when used with a hose and attachments. Also systems with higher internal resistance perform better when built with the clean-air design.

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