“conversion” type. This was the simple substitution of electrically driven pumps (fig. 21) for steam pumps in hydraulic installations. It will be recalled that pumps were necessary in cases where water main pressure was insufficient to operate the elevator directly.

In both of these cases the operational demands on the motor were of course identical to those on the prime movers which they replaced; no reversal of direction was necessary, the speed was constant, and the load was nearly constant. Furthermore, the load could be applied to the motor gradually through automatic relief valves on the pump and in the mechanical machines by slippage as the belt was shifted from the loose to the fast pulleys. The ultimate simplicity in control resulted from permitting the motor to run continuously, drawing current only in proportion to its loading. The direct-current motor of the 1880’s was easily capable of such service, and it was widely used in this way.

Larger Image
Figure 15.—Rope-geared hydraulic freight elevator
using a horizontal cylinder (about 1883).
(From a Lane & Bodley illustrated catalog of hydraulic elevators, Cincinnati, n.d.)

Larger Image Figure 16.—English direct plunger hydraulic elevator (about 1895). (From F. Dye, Popular Engineering, London, 1895, p. 280.)

Adaptation of the motor to the direct drive of an elevator machine was quite another matter, the difficulties being largely those of control. At this time the only practical means of starting a motor under load was by introducing resistance into the circuit and cutting it out in a series of steps as the speed picked up; precisely the method used to start traction motors. In the early attempts to couple the motor directly to the winding drum through worm gearing, this “notching up” was transmitted to the car as a jerking motion, disagreeable to passengers and hard on machinery. Furthermore, the controller contacts had a short life because of the arcing which resulted from heavy starting currents. In all, such systems were unsatisfactory and generally unreliable, and were held in disfavor by both elevator experts and owners.

Larger Image Figure 17.—Siemens’ electric rack-climbing elevator of 1880. (From Werner von Siemens, Gesammelte Abhandlungen und Vorträge, Berlin, 1881, pl. 5.)