FIG. 65. GOOD LOCATION FOR DUST SEPARATOR WHERE LARGE AREAS ARE SERVED BY ONE CLEANING SYSTEM.
Where the system becomes still larger, two or more separators located at centers of groups of risers can be used and clean air pipes of any desired size run to the vacuum producer ([Fig. 66]). When more than one separator is used care should be exercised in proportioning the pipe lines from the separators to the vacuum producer so as to have the friction loss from the vacuum producer to each separator the same in order to give uniform results at all inlets. This loss should also be kept as low as possible in order to prevent a high vacuum in a separator serving a portion of the system on which few sweepers are in operation. If low friction losses in the clean air pipe will require larger pipes than it is practical or economical to install, pressure reducing valves might be located in the clean air pipes near the separators to so regulate the vacuum at the separators and insure uniform results. A system of this kind might serve several premises and the air used by each be metered and the service sold much the same as heat and electricity. However, the power required to operate the system would be greater than that needed to operate a similar number of sweepers by individual plants owing to the higher vacuum required to overcome the friction in the trunk mains. This would be offset by the use of larger units and the possibility of operating them at full load at nearly all times. A system of this kind was contemplated in Milwaukee some seven years ago, but was never installed.
FIG. 66. LOCATION OF SEPARATORS AT CENTERS OF GROUPS OF RISERS FOR LARGE SYSTEMS.
The question of pipe friction in connection with the design of vacuum cleaning systems requires careful consideration, much more than it ever received in the early days of the art and a great deal more than it sometimes receives at the present time.
CHAPTER VIII.
Separators.
The appliances which remove the dust from the air current which has carried it through the hose and pipe lines, in order to prevent damage to the vacuum producer, play an important part in the make-up of a vacuum cleaning system.
Classification of Separators.
—Separators may be divided into two classes according to their use: