When you sip soda through a straw, you are utilizing the
simplest of all suction mechanisms. Sucking the soda up causes
a pressure drop between the bottom of the straw and the top of
the straw. With greater fluid pressure at the bottom than the
top, the soda is pushed up to your mouth.
In its 100-year history, the electric vacuum
cleaner has become an indispensable home appliance for
most people, and it's obvious why. Imagine picking all
this sawdust out of the carpet by
This is the same basic mechanism at work in a vacuum
cleaner, though the execution is a bit more complicated. In
this edition of HowStuffWorks,
we'll look inside a vacuum cleaner to find out how it puts
suction to work when cleaning up the dust and debris in your
house. As we'll see, the standard vacuum cleaner design is
exceedingly simple, but it relies on a host of physical
principles to clean effectively.
It may look like a complicated
machine, but the conventional vacuum cleaner is actually made
up of only six essential components:
- An intake port, which may include a variety of
- An exhaust port
- An electric motor
- A fan
- A porous bag
- A housing that contains all the other components
When you plug the vacuum cleaner in and turn it on, this is
- The electric current operates the motor.
The motor is attached to the fan, which has angled
blades (like an airplane
- As the fan blades turn, they force air forward,
toward the exhaust port (check out How
Airplanes Work to find out what causes this).
- When air particles are driven forward, the
density of particles (and therefore the air
pressure) increases in front of the fan and decreases
behind the fan.
This pressure drop behind the fan is just like the
pressure drop in the straw when you sip from your drink. The
pressure level in the area behind the fan drops below the
pressure level outside the vacuum cleaner (the ambient air
pressure). This creates suction, a partial vacuum,
inside the vacuum cleaner. The ambient air pushes itself into
the vacuum cleaner through the intake port because the air
pressure inside the vacuum cleaner is lower than the pressure
Two upright vacuum cleaner models, one with
the conventional bag system (right), and the other with
the new "cyclone" system
As long as the fan is running and the passageway through
the vacuum cleaner remains open, there is a constant stream
of air moving through the intake port and out the exhaust
port. But how does a flowing stream of air collect the dirt
and debris from your carpet? In the next section, we'll find
out how this works.
Picking Up the Dirt
In the last section, we
saw that the suction created by a vacuum cleaner's rotating
fan creates a flowing stream of air moving through the intake
port and out the exhaust port. This stream of air acts just
like a stream of water. The moving air particles rub against
any loose dust or debris as they move, and if the debris is
light enough and the suction is strong enough, the
friction carries the material through the inside of the
vacuum cleaner. This is the same principle that causes leaves
and other debris to float down a stream. Some vacuum designs
also have rotating brushes at the intake port, which
kick dust and dirt loose from the carpet so it can be picked
up by the air stream.
Upright vacuum cleaners usually have rotating
brushes on the bottom to knock dirt loose from your
carpet. The brushes may be rotated by the vacuum's motor
or simply by the rushing
As the dirt-filled air makes its way to the exhaust port,
it passes through the vacuum-cleaner bag. These bags
are made of porous woven material (typically cloth or paper),
which acts as an air filter. The tiny holes in the bag
are large enough to let air particles pass by, but too small
for most dirt particles to fit through. Thus, when the air
current streams into the bag, all the air moves on through the
material, but the dirt and debris collect in the bag.
The vacuum cleaner bag is simply a filter
that lets air pass through but keeps dirt
You can put the vacuum-cleaner bag anywhere along the path
between the intake tube and the exhaust port, as long as the
air current flows through it. In upright vacuum cleaners, the
bag is typically the last stop on the path: Immediately after
it is filtered, the air flows back to the outside. In
canister vacuums, the bag may be positioned before the
fan, so the air is filtered as soon as it enters the vacuum.
Using this basic idea, designers create all sorts of vacuum
cleaners, with a wide range of suction capacities. In the next
section, we'll look at a few of the factors that determine
In the last section, we saw
that vacuum cleaners pick up dirt by driving a stream of air
through an air filter (the bag). The power of the vacuum
cleaner's suction depends on a number of factors. Suction will
be stronger or weaker depending on:
- The power of the fan: To generate strong suction,
the motor has to turn at a good speed.
- The blockage of the air passageway: When a great
deal of debris builds up in the vacuum bag, the air faces
greater resistance on its way out. Each particle of air
moves more slowly because of the increased drag. This is why
a vacuum cleaner works better when you've just replaced the
bag than when you've been vacuuming for a while.
- The size of the opening at the end of the intake
port: Since the speed of the vacuum fan is constant, the
amount of air passing through the vacuum cleaner per unit of
time is also constant. No matter what size you make the
intake port, the same number of air particles will have to
pass into the vacuum cleaner every second. If you make the
port smaller, the individual air particles will have to move
much more quickly in order for them all to get through in
that amount of time. At the point where the air speed
increases, pressure decreases, because of Bernoulli's
principle (see How
Airplanes Work to learn about this physical principle).
The drop in pressure translates to a greater suction force
at the intake port. Because they create a stronger suction
force, narrower vacuum attachments can pick up heavier dirt
particles than wider attachments.
Vacuum cleaner attachments serve to
concentrate the flow of air as it enters the vacuum.
Since suction depends on the size and shape of the
passage, different attachments are better suited to
At the most basic level, this is all there is to a vacuum
cleaner. Since the electric vacuum's invention a century ago,
many innovative thinkers have expanded and modified this idea
to create different sorts of vacuum systems. In the next
section, we'll look at some of the more popular types of
vacuum cleaners that have popped up over the years.
All Shapes and Sizes
In the last couple of
sections, we looked at the most typical types of vacuum
cleaners: the upright and canister designs, both
of which collect dirt in a porous bag. For most of the history
of vacuum cleaners, these have been the most popular designs,
but there are many other ways to configure the suction system.
Photo courtesy Charles Lester
A Fairfax S-1 dating from the 1950s: The
Fairfax combined functionality with aesthetic
The first vacuum cleaners, dating from the mid 1800s, used
hand-operated bellows to create suction. These came in
all shapes and sizes, and were of minimal help in daily
cleaning. The first electric vacuum cleaners showed up in the
early 1900s, and were an immediate success (though for many
decades they were sold only as a luxury item).
One very popular vacuum-cleaner design from this era is all
but extinct today. This design, the central vacuum
system, turns your whole house into a cleaner. A motorized
fan in the basement or outside the house creates suction
through a series of interconnected pipes in the walls.
To use the cleaner, you turn on the fan motor and attach a
hose to any of the various pipe outlets throughout the house.
The dirt is sucked into the pipes and deposited in a large
canister, which you only empty a few times a year.
For heavy-duty cleaning jobs, a lot of people use
wet/dry vacuum cleaners, models that can pick up
liquids as well as solids. Liquid material would soak paper or
cloth filters, so these cleaners need a different sort of
collection system. The basic design is simple: On its way
through the cleaner, the air stream passes through a wider
area, which is positioned over a bucket. When it
reaches this larger area, the air stream slows down,
for the same reason that the air speeds up when flowing
through a narrow attachment. This drop in speed effectively
loosens the air's grip, so the liquid droplets and heavier
dirt particles can fall out of the air stream and into the
bucket. After you're done vacuuming, you simply dump out
whatever has collected in this bucket.
One type of wet-dry vacuum is the steam
cleaner. These vacuums dispense cleaning fluid onto the
carpet, massage it in, and then suck up the fluid along
One of the newest vacuum-cleaner variations is the
so-called "cyclone vacuum." This machine, developed in the
1980s by James Dyson, doesn't have a traditional bag or filter
system. Instead, it sends the air stream through one or more
cylinders, along a high-speed spiral path. This
motion works something like a clothes
dryer, a roller
coaster or a merry-go-round. As the air stream shoots
around in a spiral, all of the dirt particles experience a
powerful centrifugal force: They are whipped outward,
away from the air stream. In this way, the dirt is extracted
from the air without using any sort of filter. It simply
collects at the bottom of the cylinder.
The double cylinder dirt container in a
Hoover cyclone-type vacuum cleaner. As the air stream
spins around the edge of the cylinders, dirt is whipped
out so it collects at the
The cyclone system is a marked improvement on traditional
vacuum cleaners -- there are no bags to replace and the
suction doesn't decrease as you suck up more dirt. In the
future, we are sure to see more improvements on the basic
vacuum-cleaner design, with new suction mechanisms and
collection systems. But the basic idea, using a moving air
stream to pick up dirt and debris, is most likely here to stay
for some time.
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