Chapter VII

=Separators.=--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 adoption of 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.

=Vacuum Producers.=--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 in Chapter 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 in Chapter 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.

=Control.=--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 the suction 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 in Chapter 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:

=Class 1.=--Plant for residence or small office or departmental building, to be not more than one-sweeper capacity.

Renovators: See list given 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.

=Class 2.=--Large office or departmental building where carpet cleaning is important and pipe lines are of reasonable length.

Renovators: See list given 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.

=Class 3.=--Large building or group of buildings where carpet cleaning is important and long lines of piping are necessary.

Renovator: See list for “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.

=Class 4.=--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 to drive 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.