 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
colle