CHAPTER XII.Selection of Cleaning Plant.
We have considered in detail the various appliances which, taken together, make a complete vacuum cleaning system, but without considering their relation to one another. It now becomes necessary to choose an exact type and form of each of these appliances which will produce in combination a complete vacuum cleaning system best suited to the conditions to be met in a given installation.
In selecting a vacuum cleaning system consideration must be given to the character of the material to be removed, the kind and quality of the surfaces to be cleaned, the rate at which cleaning must be done, the extent of the cleaning system, and the cost of labor to operate the system, all of which must be considered in each step in the selection of a suitable plant.
In assembling the complete system, the author will take up the various parts thereof in the order in which they were discussed in the preceding chapters.
—The selection of renovators is the most important step in making up a vacuum cleaning system, as the entire makeup of the system, whether good or bad, is dependent on the proper selection of these tools. The carpet renovator is generally considered first in importance, because the cleaning of carpets has nearly always been found to be the principal field of usefulness in vacuum cleaning work. This is due, perhaps, largely to the fact that from the beginning of the art of vacuum cleaning, this function of the system has been held before the eyes of the public by the manufacturers of the earlier systems. Nearly all demonstrations of cleaning systems shown to the public consist of the removal of ordinary wheat flour from a carpet. The reason for this is two-fold; first, because it is the most striking demonstration to the eye of the layman, and, second, it is the easiest to accomplish with a small air displacementand small power, which was characteristic of the apparatus made by these manufacturers.
The author was at one time of the opinion that this function of the cleaning plant was given too much prominence by builders of systems having small air displacement, and letters were sent to the officials in charge of sixteen Government buildings in which vacuum cleaning systems were installed, asking them, among other questions, whether the cleaning system was used to any extent in cleaning bare floors, of which there were large areas, both wood and marble, in the buildings in question. The plants installed were of various makes, some of which maintained 12 in. mercury at the separator and used 1-in. hose, while about an equal number of others maintained 6 in. mercury at the separator and used 1¹⁄₂-in. hose. The answers showed that out of the sixteen buildings the cleaner was used on bare floors in but two of the buildings. One writer, who had a plant maintaining 6-in. vacuum, provided with Type F renovators and 1¹⁄₂-in. hose, stated that he had tried cleaning bare floors without success, as the renovator and hose became so clogged with litter as to be inoperative. The majority stated that the cleaning system displaced brooms on carpets and rugs and several stated that the cleaning system was used to advantage in cleaning walls, cases, pigeon holes and relief work.
This indicates that for the average office and departmental building the cleaning of carpets is the most important function of the vacuum cleaner. This is also true of residence work. Schools, department stores and manufacturing buildings contain very little floor space covered with carpets, and in buildings of this character the cleaning of bare floors is of the greatest importance. In such cases the efficiency of the carpet renovator can be sacrificed to a more efficient and economical operation of bare floor renovators.
In a building where carpet cleaning is an important function of the cleaning system, the selection of the carpet renovator is most important. Of all the various types of carpet renovators discussed inChapter III, only two need to be considered, Type A and Type F. Of these, Type A is superior in all respectsexcept the picking up of large litter, and, unless the character of the material to be removed contains a large amount of material which can be picked up by Type F renovator that will not pass Type A, Type A renovator should always be used. Even when Type F renovators are desirable, the writer considers that the plant should still contain some Type A renovators for use in places where this unusual litter will not be encountered.
Among the bare floor renovators, described inChapter IV, only the one having a felt face, curved to permit its running over the dirt, is worthy of serious consideration. This renovator requires an inlet or vacuum breaker to keep same from sticking to the surface cleaned, the extent of such opening being dependent on the vacuum maintained in the carpet renovators, as explained inChapter VII.
When carpet cleaning is considered as of secondary importance to bare floor cleaning, the degree of vacuum maintained at the separators may be reduced to that which will produce a vacuum of 1 in. mercury at the bare floor renovator, allowing the vacuum maintained at the carpet renovator to be whatever the conditions of hose and pipe line will produce. Under such conditions, the area of the inrush or vacuum breaker in the bare floor renovator may be reduced considerably.
The use of brush renovators is dependent on the capacity of the air exhauster supplied, as explained inChapter VI. If it is decided that brush renovators are necessary, then the “large volume” exhauster must be installed. The advisability of such installation is dependent on the time allowed for cleaning and the cost of the operators. In residences and small buildings where the cleaning operations can be done with one or even two domestics or laborers, very little, if any, saving in the wages of operators can be effected by increasing the rate at which the cleaning can be done. In such buildings a small-volume plant will be the most economical in first cost and operation. If such a plant is installed, the brush renovators should be omitted.
In cases where bare floor cleaning is the principal function of the cleaning system the extra quantity of air at the low vacuum necessary will not require much larger expenditure of power than that needed by the small-volume plants whenmaintaining sufficient vacuum for effective carpet cleaning and brush renovators should be provided with systems of this character.
—InChapter VIit is shown that when carpet renovators are operated efficiently in combination with bare floor renovators, 1¹⁄₄-in. hose will produce the best results with the lowest expenditure of power at the hose cock. InChapter VIIit is shown that with pipe lines of ordinary length 1¹⁄₄-in. hose also gives the best results, with the least expenditure of power at the separator, but that in cases of exceedingly long pipe lines, 1-in. hose will be the most economical. In a system where bare floor cleaning is the principal function, the vacuum to be maintained at the carpet renovator is no longer considered, and for such systems the largest hose which can easily be handled will cause the least hose friction and require the lowest vacuum at the hose cock. It is, therefore, the most economical to use on such a system. The author does not recommend the use of a hose larger than 1-³⁄₄-in. diameter for this type of plant.
The proper hose sizes, therefore, will be: For ordinary buildings where carpet cleaning is important, 1¹⁄₄-in. diameter. For installations with unusually long lines of piping, where carpet cleaning is important, 1-in. diameter.
For all systems where carpet cleaning is of secondary importance, 1¹⁄₂-in. or 1-³⁄₄-in. diameter.
—Pipe lines should always be as large as possible without reducing the velocity in same below 40 ft. per second, as explained inChapter VII.
—The type of separator to be used is dependent on the type of vacuum producer adopted. Where reciprocating exhausters are used, or other type of exhauster where there is rubbing contact between the moving parts and the dust, the combination of a wet and dry separator is recommended. When rotary or centrifugal exhausters having close clearances are used, total separators with bags are recommended. When exhausters with large clearances are operated, partial separators are satisfactory.
The use of any form of apparatus contemplating the adoptionof a satisfactory scrubbing system is not considered advisable, as the author believes that separators for handling water will be improved before scrubbing becomes commercially successful. Changes in the existing separators can be made when satisfactory scrubbing appliances are placed on the market, at no greater expense than would be necessary to bring up to date any of the present systems for handling water.
—The selection of the vacuum producer is dependent on the degree of vacuum that must be maintained to effectively operate the system selected. For the operation of a system where carpet cleaning is the principal function and 1¹⁄₄-in. hose is used, the vacuum required at the producer will be from 6 in. to 9 in. mercury. Inspection of the efficiency curves of the various types of vacuum producers, given inChapter IX, shows that the two-impeller rotary pump has the highest efficiency at this vacuum.
For the operation of systems where carpet cleaning is the most important function and 1-in. hose is found to be the most economical, 14 in. to 15 in. of vacuum at the vacuum producer is necessary, and efficiency curves, given inChapter IX, show that the piston pump is the best suited for such service.
For the operation of a system where carpet cleaning is of secondary importance a vacuum at the producer of from 2 in. to 4 in. of mercury will be sufficient. For this work, the multi-stage or even single-stage centrifugal fan is practically as efficient as the two-impeller rotary, and will be lower in first cost and cost of maintenance. Either of the above mentioned vacuum producers are satisfactory for operating a system of this type.
—Every system of more than one-sweeper capacity in which a displacement type of exhauster is used should be provided with some means of economically controlling the vacuum at the producer. On one-sweeper plants an automatic starter which will stop the motor when the vacuum reaches a point 2 in. above that required and start same when the vacuum drops to 1 in. below that required is convenient, but not necessary.
For piston pumps and all other displacement pumps fitted with eduction valves, an unloading device, which closes thesuction when the necessary vacuum is exceeded, is the least expensive to install and gives very good economy when the demand on the plant is fairly continuous during the time it is in operation. Where the service is intermittent and required at nearly all hours, the Cutler Hammer control, described inChapter X, is the most economical.
With displacement exhausters having no eduction valves, the by-pass type of control is satisfactory where the service is continuous, but is not as economical, as the unloader used with producers having eduction valves and the Cutler Hammer control is more efficient under all conditions of service. Centrifugal exhausters need no control, as vacuum control is an inherent feature of these machines.
Summing up the subject, we can divide the vacuum cleaning systems into four classes, each of which requires a different selection of appliances. They are as follows:
—Plant for residence or small office or departmental building, to be not more than one-sweeper capacity.
Renovators: Seelistgiven for “small volume” plant,Chapter IV.
Hose: 1¹⁄₄-in. diameter.
Separator: Centrifugal, dry, with bag or screen.
Vacuum Producer: Two impeller, rotary, alternate centrifugal fan. Capacity, 30 cu. ft. of free air per minute, 4 in. vacuum at producer.
Control: Automatic starter, operated by vacuum.
Size of motor: ¹⁄₂ to 1 H. P.
—Large office or departmental building where carpet cleaning is important and pipe lines are of reasonable length.
Renovators: Seelistgiven for “large volume” plant,Chapter IV.
Hose: 1¹⁄₄-in. diameter.
Separator: Centrifugal, dry, with bag or screen.
Vacuum Producer: Two impeller, rotary. Capacity, 70 cu. ft. of free air per minute for each sweeper of plant capacity at 7 in. to 9 in. vacuum.
Size of motor: 2¹⁄₂ H. P. per sweeper capacity.
Control: Cutler Hammer.
—Large building or group of buildings where carpet cleaning is important and long lines of piping are necessary.
Renovator: Seelistfor “large volume” plants,Chapter IV.
Hose: 1-in. diameter.
Separators: One centrifugal dry and one wet.
Vacuum Producer: Piston type pump. Capacity, 45 cu. ft. of free air per minute for each sweeper of plant capacity at 14 in. vacuum.
Size of motor: 4 H. P. for each sweeper of plant capacity.
Control: Automatic unloader for continuous service. Cutler Hammer for intermittent work at all times.
—Large or small plant where carpet cleaning is not an important function of the cleaning system.
Renovators: Same as for Class 3.
Hose: 1¹⁄₂ in. or 1-³⁄₄ in.
Separators: One centrifugal, dry, with or without bag, according to type of exhauster adopted.
Vacuum Producer: Centrifugal fan or two-impeller rotary pump.
Capacity: 70 to 90 cu. ft. of free air per minute for each sweeper of plant capacity, with a vacuum of from 2 in. to 3 in. mercury.
Size of motor: 1 to 2 H. P. for each sweeper of plant capacity.
Control: With centrifugal fan, none; with pump, Cutler Hammer.
It is interesting to note that to produce the most efficient plant for all of the four cases named, all of the various types of vacuum cleaning systems which have come into general use have to be operated each under its most favorable conditions and the engineer should select his plant to best fulfill the conditions of the special case at hand, just as he would select his prime mover for an electric generating plant according to its size and location. There should be no more reason why any one of these systems should attempt to fulfill the requirements of every installation than there would be for a manufacturer of steam engines to attempt to use the same type of engine todrive a generator under all conditions. The writer believes that this condition will soon be realized by all manufacturers of vacuum cleaning systems and that they will endeavor to install apparatus of the type best suited to the conditions to be met in each case.