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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 canisters and power teams, 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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