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, Micron, 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.
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