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, 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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