Chapter 4

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.

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]

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.

Epilogue

In 1900, after the customary 11-year period, Paris again prepared for an international exposition, about 5 years too early to take advantage of the great progress made by the electric elevator. When the Roux machines, the weakest element in the Eiffel Tower system, were replaced at this time, it was by other hydraulics. Built by the well known French engineering organization of Fives-Lilles, the new machines were the ultimate in power, control, and general excellence of operation. As in the Otis system, the cars ran all the way to the second platform.

The Fives-Lilles equipment reflected the advance of European elevator engineering in this short time. The machines were rope-geared and incorporated the elegant feature of self-leveling cabins which compensated for the varying track inclination. For the 1900 fair, the Otis elevator in the south pier was also removed and a wide stairway to the first platform built in its place. In 1912, 25 years after Backmann's startling proposal to use electricity for his system, the remaining Otis elevator was replaced by a small electric one. This innovation was reluctantly introduced solely for the purpose of accommodating visitors in the winter when the hydraulic systems were shut down due to freezing weather. The electric elevator had a short life, being removed in 1922 when the number of winter visitors increased far beyond its capacity. However, the two hydraulic systems were modified to operate in freezing temperatures--presumably by the simple expedient of adding an antifreezing chemical to the water--and operation was placed on a year-round basis.

Today the two Fives-Lilles hydraulic systems remain in full use; and visitors reach the Tower's summit by Edoux's elevator (fig. 41), which is all that remains of the original installation.

BALANCE OF THE THREE ELEVATOR SYSTEMS

_The Otis System_

Negative effect

Weight of cabin: 23,900 lb. × sin 78°9' (incline of upper run) 23,390 lb. Live load: 40 persons @150 lb. = 6,000 × sin 78°9' 5,872 ------ -- 29,262 lb.

Positive effect

Counterweight: 55,000 × sin 54°35' (incline of lower run) ------------------------------------------ 3 (rope gear ratio) 14,940 lb.

Weight of piston and chariot: 33,060 × sin 54°35' ------------------ 12 (ratio) 2,245

Power: 156 p.s.i. × 1,134 sq. in. (piston area) ---------------------------------------- 12 (ratio) 14,742 31,927 lb.

Excess to overcome friction 2,665 lb.

_The Roux, Combaluzier and Lepape System_

Negative effect

Weight of cabin: 14,100 × sin 54°35' 11,500 lb. Live load: 100 persons @150 lb. = 15,000 × sin 54°35' 12,220 ------ -- 23,720 lb.

Positive effect

Counterweight: 6,600 × sin 54°35' 5,380

Power: 156 p.s.i. × 2 (pistons) × 1,341.5 sq. in. (piston area) ------------------------------------------ 13 (ratio) 32,196 37,576 lb. ------ ---------- Excess to overcome friction 13,856 lb.

_The Edoux System_

Negative effect

Unbalanced weight of plungers (necessary to raise full lower car and weight of cables on lower side) 42,330 lb.

Live load: 60 persons @150 lb. 9,000 ------ -- 51,330 lb.

Positive effect

Power: 227.5 p.s.i. × 2 (plungers) × 124 sq. in. (plunger area) 56,420 lb. ---------- Excess to overcome friction 5,090 lb.

Footnotes:

[1] Translated from Jean A. Keim, _La Tour Eiffel_, Paris, 1950.

[2] The foundation footings exerted a pressure on the earth of about 200 pounds per square foot, roughly one-sixth that of the Washington Monument, then the highest structure in the world.

[3] A type of elevator known as the "teagle" was in use in some multistory English factories by about 1835. From its description, this elevator appears to have been primarily for the use of passengers, but it unquestionably carried freight as well. The machine shown in figure 7 had, with the exception of a car safety, all the features of later systems driven from line shafting--counterweight, control from the car, and reversal by straight and crossed belts.

[4] The Otis safety, of which a modified form is still used, consisted essentially of a leaf wagon spring, on the car frame, kept strained by the tension of the hoisting cables. If these gave way, the spring, released, drove dogs into continuous racks on the vertical guides, holding the car or platform in place.

[5] A notable exception was the elevator in the Washington Monument. Installed in 1880 for raising materials during the structure's final period of erection and afterwards converted to passenger service, it was for many years the highest-rise elevator in the world (about 500 feet), and was certainly among the slowest, having a speed of 50 feet per minute.

[6] Today, although not limited by the machinery, speeds are set at a maximum of about 1,400 feet per minute. If higher speeds were used, an impractically long express run would be necessary for starting and stopping in order to prevent an acceleration so rapid as to be uncomfortable to passengers and a strain on the equipment.

[7] Two machines, by Otis, in the Demarest Building, Fifth Avenue and 33d Street, New York. They were in use for over 30 years.

[8] Although the eventually successful application of electric power to the elevator did not occur until 1904, and therefore goes beyond the chronological scope of this discussion, it was of such importance insofar as current practice is concerned as to be worthy of brief mention. In that year the first gearless traction machine was installed by Otis in a Chicago theatre. As the name implies, the cables were not wrapped on a drum but passed, from the car, over a grooved sheave directly on the motor shaft, the other ends being attached to the counterweights. The result was a system of beautiful simplicity, capable of any rise and speed with no proportionate increase in the number or size of its parts, and free from any possibility of car or weights being drawn into the machinery. This system is still the only one used for rises of over 100 feet or so. By the time of its introduction, motor controls had been improved to the point of complete practicability.

[9] Mechanical transmission of power by wire rope was a well developed practice at this time, involving in many instances high powers and distances up to a mile. To attempt this system in the Eiffel Tower, crowded with structural work, machinery and people, was another matter.

[10] According to Otis Elevator Company, the final price, because of extras, was $30,000.

[11] In _Pall Mall Gazette_, as quoted in _The Engineering and Building Record and the Sanitary Engineer_, May 25, 1889, vol. 19, p. 345.

[12] From speech at annual summer meeting of Institution of Mechanical Engineers, Paris, 1889. Quoted in _Engineering_, July 5, 1889, vol. 48, p. 18.

[13] Located near the Tower, built for the Paris fair of 1878.

[14] Improved oil-well drilling techniques were influential in the intense but short burst of popularity enjoyed by direct plunger systems in the United States between 1899 and 1910. In New York, many such systems of 200-foot rise, and one of 380 feet, were installed.

[15] An obvious question arises here: What prevents a plunger 200 or 300 feet long and no more than 16 inches in diameter from buckling under its compressive loading? The answer is simply that most of this length is not in compression but in tension. The Edoux rams, when fully extended, virtually hung from the upper car, sustained by the weight of 500 feet of cable on the other side of the sheaves. As the upper car descended this effect diminished, but as the rams moved back into the cylinders their unsupported length was correspondingly reduced.

[16] M. A. Ansaloni, "The Lifts in the Eiffel Tower," quoted in _Engineering_, July 5, 1889, vol. 48, p. 23. The strength of steel when drawn into wire is increased tremendously. Breaking stresses of 140,000 p.s.i. were not particularly high at the time. Special cables with breaking stresses of up to 370,000 p.s.i. were available.

Transcriber's Notes:

Passages in italics are indicated by _underscore_.

The original was printed in two columns per page.

Illustrations have been moved to the nearest paragraph break.

The following misprints have been corrected: "Trevethick's" corrected to "Trevithick's" (page 5) "then" corrected to "than" (page 14) "smiliar" corrected to "similar" (page 31)