So Powerful that it can Pick Up Steel Balls
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!
The ability of a vacuum cleaner to pick up steel balls
seems to be quite impressive, especially a number of them
in rapid succession as seen on television commercials by
Royal and
Eureka. Typically uprights have medium
to poor suction when used
with a hose and attachments as discussed in our article on
Compromises with Modern Uprights.
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. As air flow is restricted, the air
pressure within the vacuum cleaner, hose, etc. drops closer to the
pressure that is at the fan. It is the force exerted by this
difference between normal and reduced air pressure which picks up
the steel balls. 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 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 a vacuum cleaner with only 30" of water lift would
exert about 1 pound per square inch on a steel ball. The
steel balls are aproximately 1" in diameter, giving about 0.78 square
inches of cross sectional area so the force exerted to pick up a
3 ounce steel ball is about 12 ounces. While
canister type vacuum
cleaners measure from 60 to 103 inches of water lift, most
upright types with on-board
attachments only measure 30 to 60 inches of water lift. Since
the force exerted is proportional to the area, even more
impressive demonstrations can be done as explained in our
article titled
"So Powerful that it can Lift an Adult Person."
As you can see, it really isn't such a marvel that an upright
can pick up steel balls. 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.
