FIG. 90. LATE TYPE OF CENTRIFUGAL EXHAUSTER MADE BY THE SPENCER TURBINE CLEANER COMPANY.
The efficiency is fairly constant between 6-in. and 10-in. vacuum and is much higher than is obtained with any of the other types of pumps at these vacua. When they are operated at higher vacuum the efficiency is about the same as obtained with the sliding vane pumps and lower than that obtained with the reciprocating pumps. The best efficiency of this pump is at the vacuum necessary to operate a cleaning system provided with 1¹⁄₄-in. hose.
A slight modification of this type of pump is that used by the Vacuum Engineering Company, known as the Rotrex. This pump has but one impeller, of nearly the same form as the impellers in the Root blowers and has a follower driven by crank and connecting rods which is always in close proximity to the impeller but does not touch same. The arrangement of this pump is illustrated in [Fig. 89] which also shows the saturation chamber and screens used instead of a separator, as explained in [Chapter VIII].
FIG. 91. POWER AND EFFICIENCY CURVES FOR THE SPENCER MACHINE.
The author has never tested the economy of these pumps but would infer that their economy should be about the same as that of the Root blower.
Centrifugal Exhausters.
—This type of exhauster has always taken the form of a fan. The first stationary fan type of exhauster was manufactured by the Spencer Turbine Cleaner Company. Their latest type is illustrated in [Fig. 90]. It consists of a series of centrifugal fans mounted on a vertical shaft, stationary deflection blades being provided between the wheels to conduct the air from the periphery of one wheel to the center of the next.
FIG. 92. INTERIOR ARRANGEMENT OF INVINCIBLE MACHINE, MANUFACTURED BY THE ELECTRIC RENOVATOR MANUFACTURING COMPANY.