Such a cleaner would not be portable in the sense of the term as applied to the most popular cleaners today. The same type has been built on special order by the American Radiator Company, which mounted its 1¹⁄₂ H. P. Arco Wand machine on a truck. This cleaner weighs several hundred pounds and could be moved up and down stairs about as easily as a sewing machine and would not be of any service in a building not equipped with elevators. The power required to operate this cleaner is also so great that special power wiring and large capacity outlet plugs have to be installed throughout the building. Such equipment has been provided in at least two department stores where these cleaners are in use. This means that one wires his building for vacuum cleaning instead of piping it, and there is also the necessity of moving a heavy machine about to do the same work as a stationary plant.
It would appear to the author that the cost of wiring would about equal that of piping and that the additional labor required to move the machine about would cost as much as the additional power needed by the stationary exhauster.
This cleaner, as well as all other portable cleaners, discharges the air from the exhauster directly back into the apartment cleaned, and is open to the same objection that was raised against the early compressed air cleaners. While all the dust may be caught by the dust bag, the microbes are allowed to escape with the air and the cleaner is not a sanitary device by any manner of means.
There are a few portable machines using rotary exhausters of the Root type, and piston pumps, all of which are heavy to move about and, in making them as light as possible, the efficiency of the exhauster has been sacrificed. These machines will do the same quality of cleaning as the stationary plants recommended for residence work and they require about ³⁄₄ H. P., which is no less than is needed for a stationary plant of the same capacity and efficiency.
The most popular type of portable cleaner is one which can be attached to a socket or plug connected with the lighting system. This should limit the power consumption to ¹⁄₈ H. P. However, many of these cleaners use as much as 400 watts and a fair average for cleaners retailing at about $125.00 is 250 watts. Such cleaners will exhaust about 25 cu. ft. of air with a vacuum of 1 in. mercury at the vacometer, a ⁵⁄₈-in. orifice being used. The theoretical power required to move the air is approximately 50 watts and the overall efficiency of these cleaners is, therefore, about 20%, as against 40% to 50% in a good, one-sweeper stationary plant. The power expended in operating these portable cleaners in proportion to the work done is no less than with an efficient stationary plant.
Portable cleaners have been made in many types but practically all the standard makes use one or two forms of vacuum producers, either the diaphragm pump or the single or multi-stage fan. The pumps of the former type are able to produce a vacuum as high as 6 in. to 10 in. of mercury, when no air is passing, and will displace as high as 30 cu. ft. of free air per minute, when operated with a free inlet. They produce about 1 in. of mercury at the carpet renovator when operated on an ordinary carpet. When small-sized upholstery renovators are used, a much higher vacuum is possible. When operated with bare floor renovators or brushes, the quantity of air exhausted is not much over 20 cu. ft. per minute and they make very inefficient bare floor and wall cleaners, but will do thorough carpet and upholstery cleaning provided a small enough renovator is used.
Machines using a multi-stage fan will produce a maximum vacuum of approximately 2 in. of mercury when exhausting no air, and will produce a vacuum of approximately 1 in. of mercury when operated on an ordinary carpet. With an unrestricted inlet, they will exhaust from 40 to 50 cu. ft. of air per minute. When operated on a bare floor, they will exhaust approximately 30 cu. ft. of free air per minute. They are, therefore, more efficient floor cleaners than the pumps, but cannot do thorough carpet and upholstery cleaning, no matter how small the renovator.
The smaller-fan type of machines, in which the fan is placed integral with the carpet renovator and in which hose is not used in cleaning floors or carpets, are provided with a single-stage fan. They produce a suction of not exceeding ¹⁄₂ in. of mercury when no air is exhausted and will exhaust from 5 to 10 cu. ft. of free air per minute when operated on a carpet. With a free inlet they will exhaust from 15 to 20 cu. ft. of free air per minute. These machines are little if any better than ordinary carpet sweepers.
Machines of this type are open to another objection in that the dust bag is placed on the outlet of the fan and the dust in the bag is continually agitated by the passage of the air, with the result that all the finer particles of the dust are blown through the bag back into the apartment. To be effective, the dust bag must always be placed on the suction side of the exhauster and should be so arranged that the dust will not quickly cover the entire area of the bag, for, when this occurs, the suction is quickly reduced to such an extent that no further cleaning can be done until the bag has been cleaned.
There is another type of mechanical cleaner manufactured by the Hoover Suction Sweeper Company which is provided with a mechanically-operated brush for loosening the dirt from the carpet. The dust is then conveyed through a single-stage fan to a dust bag. The cleaner does not depend on the vacuum to loosen the dirt and will do quite effective carpet cleaning with a small expenditure of power. Owing to the small suction produced, it is of little value for cleaning anything but carpets.