So Powerful that it can Lift an Adult Person
The power of a vacuum cleaner motor is one of the most
misrepresented and misunderstood aspects of vacuum cleaner
technology. This confusion has been accentuated by many
manufacturers and salespersons in their attempt to make their
products appear superior to others. At times this takes the form
of performing amazing demonstrations of the vacuum cleaner's
abilities. Often, when analyzed with a few basic laws of physics
in mind, these amazing feats prove very little and are relatively
meaningless!
A number of years ago, while attending a trade show, I saw an
interesting demonstration where a canister type of vacuum cleaner
was used to lift an adult person. A large clear cylinder was
supported overhead by a tripod made of three steel tubes. The top
of the cylinder was closed except for a tube at the center where
the hose from the vacuum cleaner was attached. The bottom of the
cylinder was closed also except for a hole through which the rod
connecting the piston to the seat frame passed. Within the
cylinder was a piston which could be pulled upward by the suction
of the vacuum cleaner. The seat and frame were constructed so that
a person could sit in the seat and be lifted as the piston was
pulled upward. I don't know the exact diameter of the cylinder
and piston but I think it was twelve to fifteen inches.
The laws of physics behind this feat are rather simple. As
explained in our article on the
Fan or Impeller, a partial
vacuum (area of reduced air pressure)
is produced by the spinning fan.
The difference in pressure between the normal atmospheric pressure
and the reduced air pressure in the fan is what normally causes air
to flow toward the fan. If air flow is prevented, the air pressure
within the vacuum cleaner, hose, etc. drops to the same pressure as
at the fan. It is the force exerted by this difference between
normal and reduced air pressure which moves the piston upward,
lifting the person. This force is proportional to the area upon
which it is applied as described below.
The unit of measurement for pressure is often stated as force
per area as in "pounds per square inch", etc. An alternate
expression of pressure or pressure difference is to state how high
in a tube a liquid of known weight is pushed or pulled. Examples
of this are the barometer (calibrated in millimeters of mercury or
millibars of pressure) for measuring atmospheric pressure and the
sealed suction gauge (calibrated in
inches of water lift) for measuring
the suction (difference in air pressure mentioned above) of a
vacuum cleaner.
One cubic inch of water weighs 0.036 pounds so the pressure
difference (sealed suction) for a vacuum cleaner which measures 100"
of water lift on a suction gauge is 3.6 pounds per square inch. A bit
of math shows us that it would take a vacuum cleaner rated at 62"
of water lift to exert around 2.2 pounds per square inch on the
12" piston (area of 113 square inches) to lift a person and chair
weighing 250 pounds. Since the force exerted is proportional to the area
of the piston, a 15" diameter piston would only require a vacuum cleaner
rated at 40" of water lift to lift the person! A canister type of
vacuum cleaner with poor suction typically will measure around
70" of water lift while the most powerful ones measure around 103" of
water lift.
As you can see, it really isn't such a marvel that an average
vacuum cleaner can lift an adult person. To learn about
various methods for rating vacuum cleaner motors, see our article
about the Power of the Suction Motor.
There are many important performance aspects of a vacuum
cleaner system which you can read about in our article on
Identifying Good Performance Factors. These
include the Power of the Suction Motor,
Effects of Brushing Action,
effect of internal resistance
on the Air Flow through the System,
as well as the Efficiency of Paper Bags and
Filtration Efficiency - HEPA, ULPA, etc.
To choose a durable vacuum cleaner which will meet your cleaning tasks and
preferences, see our articles on
Identifying Durable Designs & Construction
and Match Your Tasks and Cleaning Style. A
good, knowledgeable sales person like those at Ristenbatt Vacuum
Cleaner Service can help you determine which vacuum cleaner system
will be the best for you in your particular cleaning situation.
