You Can Clean Your Pillows with a Large Bag
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 salespersons who sell their vacuum cleaners by performing
demonstrations in the homes of their prospective customers are
known for doing some amazing feats with their products. One
such activity is to take a pillow from a sofa or bed and place it
in a large clear bag. The open end of the bag is held tightly over
the end of the vacuum cleaner hose so that most of the air is removed
from the plastic bag. As you can imagine, the pillow is
compressed until it is quite thin. The salesperson usually
explains that the person can even use their vacuum cleaner to "freshen"
or clean their pillows with this technique. While it looks
impressive to have the pillow flattened so greatly, it has very little,
if any, effect on cleaning the pillow since there is an absence of
a strong air flow
to remove the dirt. It is therefore relatively meaningless.
The laws of physics behind this demonstration 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 collapses the plastic bag.
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 a poor canister type vacuum cleaner rated
at only 70" of water lift would exert around 2.5 pounds per square
inch on the pillow. The flat side of a typical sofa pillow has
about 440 square inches of area. Therefore, over 1000 pounds
of force is exerted on the pillow to flatten it. The most
powerful canister type vacuum cleaners measure around 103" of
water lift. Since this demonstration does not accurately show the
actual power or cleaning ability of the vacuum cleaner, it is
relatively meaningless.
As you can see, it really isn't such a marvel that a pillow
can be compressed so greatly. 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.
