When the vacuum cleaning systems combine scrubbing with dry cleaning, the separator and vacuum producer must provide for the removal of water as well as air. A few manufacturers have attempted this, among which are the makers of the Rotrex system, described in [Chapter IX], in which the water is passed through the pump and into the sewer under sufficient pressure to overcome the friction in the exhaust pipe through which the expelled air passes after leaving the separator. This may be sufficient to force the trap seals of the plumbing system, and, if used, the discharge connection should be made to the sewer outside the main running trap, close to the fresh air inlet. As large articles cannot be allowed to pass through the pump, a screen is necessary on the inlet side of the vacuum producer, but this may give trouble, due to the clogging with litter.
The Atwood Vacuum Cleaner Company uses a wet tank on the suction side of the vacuum producer into which the dirt and water are discharged, the air being separated and passed to the vacuum producer. When this tank becomes partly filled it is necessary to shut down the plant and empty the contents of the tank by gravity into the sewer.
This method overcomes the objections to clogged screens and forced trap seals, and all litter is discharged direct to the sewer, together with a quantity of water which is presumably sufficient to flush the litter through the sewer. The last named system is still open to two objections; first, it is not automatic, and, if neglected, the tank will fill with water and force same into the vacuum producer. With the Root type of vacuum pump this will do little harm unless a large quantity of floating litter should pass into the pump. Second, the system may be operated with dry renovators exclusively for a considerable portion of the time, in which case the contents of the separator may become of such a consistency as will not readily flush through the sewer, and stoppage of the same may occur.
Another separator of this type has recently been patented by E. B. Dunn, the originator of the Dunn Locke, in which the mud and the water are automatically discharged alternately from one of two separators, as described in [Chapter VIII].
Such a separator, in which sufficient water is automatically introduced to dilute the dirt and which will automatically empty when sufficiently filled, when so constructed that it will operate continuously, is considered to be the ideal separator for use with a combined cleaning and scrubbing system. Until the mechanical scrubber and an automatically operated separator are commercially introduced the author does not consider that the use of scrubbing attachments, in connection with the vacuum cleaning system, is advisable.
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.