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Air Flow through the Vacuum Cleaner System
Air flow is the movement of air from one
location to another. In a vacuum cleaner, it generally refers to the
movement of air through the vacuum cleaner or central vacuum system. It,
combined with agitation, is the most
important aspect of cleaning with a vacuum cleaner. It is the force
exerted by the moving air which actually picks up the dirt and moves it
into the bag or dirt container.
You will sometimes see the Air Flow in Cubic Feet Per Minute (CFM) rated for a vacuum cleaner. While the air
flow rating is not a direct rating of the power of the suction motor, it
is affected by its suction. The air flow rating is typically obtained by
measuring the air flow through the vacuum cleaner with no hose nor
attachments connected to it. Keep in mind that the same air moves through
the entire vacuum cleaner system so the actual air flow in use is
proportional to the amount of suction produced by the motor and inversely
proportional to the total resistance to air
flow throughout the system.
The air is motivated to move by the reduced
air pressure created by the suction motor. The
easier it is for the air to flow, the better the cleaning performance will
be. Also, the stronger the suction created
by the suction motor is, the better the air flow will be. There are many
variables which affect the actual air flow in a system which are not
reflected in the air flow rating. In addition to the
resistance within the actual vacuum cleaner,
there is resistance caused by air turbulence in the hose and tubing,
restriction where the cleaning nozzle contacts the floor, as well as
increased resistance within the filtration system as the unit fills with
dirt. Therefore it is important to compare the
sealed suction along with the air flow when
comparing canisters, power teams, and central vacuum systems. The quality of the paper bag can have a significant impact on the air
flow through the system. While the bag's filter media must be able to stop
the fine dust and allergens, it should present the least amount of
resistance to air flow that is possible. The
total resistance of the paper bag is inversely proportional to the total
area of the filter media. In other words, doubling the area of a paper
bag's surface will cut the total resistance to air flow in half. Therefore, if two different size bags are constructed of the same quality
filter media, the larger one will enhance the cleaning performance by
making it easier for the air to flow. To learn more about how the quality
of the paper bag affects the air flow, read our article on the
Dustbag Performance and Filtration Efficiency.
Another factor is the distance and cross sectional area of the passages
through which the air must travel through the system. This is one area in
which the Traditional Upright really shines.
In these the air flows a relatively short distance through large passages
into large area paper bags so there is a huge amount of air flow. The
Commercial Eureka uprights,
Commercial and Heavy Duty Sanitaire
uprights by Electrolux Home Care Products North America
(formerly The Eureka Company)
and Kirby uprights are examples of
traditional uprights which combine this
design with large diameter fans for
outstanding carpet cleaning performance.
For any given air flow, the speed of the
moving air is inversely proportional to the area of the opening through
which it is passing. A more narrow opening in the nozzle will produce a
faster air flow velocity, enacting more force to pick up the dirt. This
is why a small attachment is more effective in picking up stubborn dirt.
For best performance the nozzle should also be designed so it produces
similar air flow velocity across its complete width, not just near the air
passage leading from it. Some uprights and power nozzles incorporate a
center mounted air intake behind or above the brush roll which flares out
to the edges of the cleaning nozzle as it approaches the brush roll. This
wide funnel shaped opening causes the air flow to be distributed quite
evenly across the entire cleaning width for more efficient and uniform
cleaning. This also creates a dirt collection area immediately behind or
above the brush roll so dirt and grit are gathered and whisk away by the
air flow before they can bounce back out of the nozzle. This substantially
reduces the scatter effect which many uprights experience when picking up
grit and small stones. This design is discussed in more detail in our
article on Cleaning Nozzle Design.
PageType: Educational
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