THE EDOUX SYSTEM
The section of the Tower presenting the least difficulty to elevator installation was that above the juncture of the four legs—from the second platform to the third, or observation, enclosure. There was no question that French equipment could perform this service. The run being perfectly straight and vertical, the only unusual demand upon contemporary elevator technology was the length of rise—525 feet.
The system ultimately selected ([fig. 37]) appealed to the Commission largely because of a similar one that had been installed in one tower of the famous Trocadero[13] and which had been operating successfully for 10 years. It was the direct plunger system of Leon Edoux, and was, for the time, far more rationally contrived than Backmann’s helicoidal system. Edoux, an old schoolmate of Eiffel’s, had built thousands of elevators in France and was possibly the country’s most successful inventor and manufacturer in the field. It is likely that he did not attempt to obtain the contract for the elevator equipment in the Tower legs, as his experience was based almost entirely on plunger systems, a type, as we have seen, not readily adaptable to that situation. What is puzzling was the failure of the Commission’s members to recognize sooner Edoux’s obvious ability to provide equipment for the upper run. It may have been due to their inexplicable confidence in Backmann.
Figure 31.—The French Girard pumps that supplied the Otis and Roux systems.
(From La Nature, Oct. 5, 1889, vol. 17, p. 292.)
The direct plunger elevator was the only type in which European practice was in advance of American practice at this time. Not until the beginning of the 20th century, when hydraulic systems were forced into competition with electrical systems, was the direct plunger elevator improved in America to the extent of being practically capable of high rises and speeds. Another reason for its early disfavor in the United States was the necessity for drilling an expensive plunger well equal in length to the rise.[14]
As mentioned, the most serious problem confronting Edoux was the extremely high rise of 525 feet. The Trocadero elevator, then the highest plunger machine in the world, traveled only about 230 feet. A secondary difficulty was the esthetic undesirability of permitting a plunger cylinder to project downward a distance equal to such a rise, which would have carried it directly into the center of the open area beneath the first platform ([fig. 6]). Both problems were met by an ingenious modification of the basic system. The run was divided into two equal sections, each of 262 feet, and two cars were used. One operated from the bottom of the run at the second platform level to an intermediate platform half-way up, while the other operated from this point to the observation platform near the top of the Tower. The two sections were of course parallel, but offset. A central guide, on the Tower’s center-line, running the entire 525 feet served both cars, with shorter guides on either side—one for the upper and one for the lower run. Thus, each car traveled only half the total distance. The two cars were connected, as in the Backmann system, by steel cables running over sheaves at the top, balancing each other and eliminating the need for counterweights. Two driving rams were used. By being placed beneath the upper car, their cylinders extended downward only the 262 feet to the second platform and so did not project beyond the confines of the system itself.[15] In making the upward or downward trip, the passengers had to change from one car to the other at the intermediate platform, where the two met and parted ([fig. 39]). This transfer was the only undesirable feature of what was, on the whole, a thoroughly efficient and well designed work of elevator engineering.
Figure 32.—The Otis distributor, with valves shown in motionless, neutral position.
Since the main valve at all times was subjected to the full operating pressure, it
was necessary to drive this valve with a servo piston. The control cable operated
only the servo piston’s valve. (Adapted from Gustave Eiffel, La Tour de Trois
Cents Mètres, Paris, 1900, p. 130.)
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Figure 33.—General arrangement of the Roux Combaluzier and Lepape elevator.
Figure 34.—Roux, Combaluzier and Lepape machinery and cabin at the Tower’s base.
(From La Nature, Aug. 10, 1889, vol. 17, p. 168.)
In operation, water was admitted to the two cylinders from a tank on the third platform. The resultant hydraulic head was sufficient to force out the rams and raise the upper car. As the rams and car rose, the rising water level in the cylinders caused a progressive reduction of the available head. This negative effect was further heightened by the fact that, as the rams moved upward, less and less of their length was buoyed by the water within the cylinders, increasing their effective weight. These two factors were, however, exactly compensated for by the lengthening of the cables on the other side of the pulleys as the lower car descended. Perfect balance of the system’s dead load for any position of the cabins was, therefore, a quality inherent in its design. However, there were two extreme conditions of live loading which required consideration: the lower car full and the upper empty, or vice versa. To permit the upper car to descend under the first condition, the plungers were made sufficiently heavy, by the addition of cast iron at their lower ends, to overbalance the weight of a capacity load in the lower car. The second condition demanded simply that the system be powerful enough to lift the unbalanced weight of the plungers plus the weight of passengers in the upper car.
As in the other systems, safety was a matter of prime importance. In this case, the element of risk lay in the possibility of the suspended car falling. The upper car, resting on the rams, was virtually free of such danger. Here again the influence of Backmann was felt—a brake of his design was applied ([fig. 38]). It was, true to form, a throwback, similar safety devices having proven unsuccessful much earlier. Attached to the lower car were two helically threaded vertical rollers, working within the hollow guides. Corresponding helical ribs in the guides rotated the rollers as the car moved. If the car speed exceeded a set limit, the increased resistance offered by the apparatus drove the rollers up into friction cups, slowing or stopping the car.
| Figure 35.—Detail of links in the Roux system. (From Gustave Eiffel, La Tour de Trois Cents Mètres, Paris, 1900, p. 156.) | Figure 36.—Section of guide trunks in the Roux system. (From Gustave Eiffel, La Tour de Trois Cents Mètres, Paris, 1900, p. 156.) |
The device was considered ineffectual by Edoux and Eiffel, who were aware that the ultimate safety of the system resulted from the use of supporting cables far heavier than necessary. There were four such cables, with a total sectional area of 15.5 square inches. The total maximum load to which the cables might be subjected was about 47,000 pounds, producing a stress of about 3,000 pounds per square inch compared to a breaking stress of 140,000 pounds per square inch—a safety factor of 46![16]
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| Figure 37.—Schematic diagram of the Edoux system. (Adapted from Gustave Eiffel, La Tour de Trois Cents Mètres, Paris, 1900, p. 175.) | Figure 38.—Vertical section through lower (suspended) Edoux car, showing Backmann helicoidal safety brake. (Adapted from Gustave Eiffel, La Tour Eiffel en 1900, Paris, 1902, p. 12.) |
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A curiosity in connection with the Edoux system was the use of Worthington (American) pumps ([fig. 40]) to carry the water exhausted from the cylinders back to the supply tanks. No record has been found that might explain why this particular exception was made to the “foreign materials” stipulation. This exception is even more strange in view of Otis’ futile request for the same pumps and the fact that any number of native machines must have been available. It is possible that Edoux’s personal influence was sufficient to overcome the authority of the regulation.
Figure 39.—Passengers changing cars on Edoux elevator at intermediate platform.
(From La Nature, May 4, 1889, vol. 17, p. 361.)
Figure 40.—Worthington tandem compound steam pumps, at base of the Tower’s south pier,
supplied water for the Edoux system. The tank was at 896 feet, but suction was taken from
the top of the cylinders at 643 feet; therefore, the pumps worked against a head of only
about 250 feet. (From La Nature, Oct. 5, 1889, vol. 17, p. 293.)
Figure 41.—Recent view of lower car of the Edoux system,
showing slotted cylindrical guides that enclose the cables.