Chapter III: , only two need to be considered, Type A and Type F. Of

these, Type A is superior in all respects except 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 in Chapter 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 in Chapter 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 in Chapter 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 when maintaining sufficient vacuum for effective carpet cleaning and brush renovators should be provided with systems of this character.

=Hose.=--In Chapter VI it 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. In Chapter VII it 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.=--Pipe lines should always be as large as possible without reducing the velocity in same below 40 ft. per second, as explained in