Chapter II: Part 2

To penetrate the inventive rationale behind this strange machine is not difficult. Aware of the fundamental dictum of absolute safety before all else, the Roux engineers turned logically to the safest known elevator type--the direct plunger. This type of elevator, being well suited to low rises, formed the main body of European practice at the time, and in this fact lay the further attraction of a system firmly based on tradition. Since the piers between the ground and first platform could accommodate a straight, although inclined run, the solution might obviously have been to use an inclined, direct plunger. The only difficulty would have been that of drilling a 220-foot, inclined well for the cylinder. While a difficult problem, it would not have been insurmountable. What then was the reason for using a design vastly more complex? The only reasonable answer that presents itself is that the designers, working in a period before the Otis bid had been accepted, were attempting to evolve an apparatus capable of the complete service to the second platform. The use of a rigid direct plunger thus precluded, it became necessary to transpose the basic idea in order to adapt it to the curvature of the Tower leg, and at the same time retain its inherent quality of safety. Continuing the conceptual sequence, the idea of a plunger made in some manner flexible apparently suggested itself, becoming the heart of the Roux machines.

Here then was a design exhibiting strange contrast. It was on the one hand completely novel, devised expressly for this trying service; yet on the other hand it was derived from and fundamentally based on a thoroughly traditional system. If nothing else, it was safe beyond question. In Eiffel's own words, the Roux lifts "not only were safe, but appeared safe; a most desirable feature in lifts traveling to such heights and carrying the general public."[12]

The system's shortcomings could hardly be more evident. Friction resulting from the more than 320 joints in the flexible pistons, each carrying two rollers, plus that from the pitch chains must have been immense. The noise created by such multiplicity of parts can only be imagined. Capacity was equivalent to that of the Otis system. About 100 people could be carried in the double-deck cabin, some standing. The speed, however, was only 200 feet per minute, understandably low.

If it had been the initial intention of the designers to operate their cars to the second platform, they must shortly have become aware of the impracticability of this plan, caused by an inherent characteristic of the apparatus. As long as the compressive force acted along the longitudinal axis of the links, there was no lateral resultant and the only load on the small rollers was that due to the dead weight of the link itself. However, if a curve had been introduced in the guide channels to increase the incline of the upper run, as done by Otis, the force on those links traversing the bend would have been eccentric--assuming the car to be in the upper section, above the bend. The difference between the two sections (based upon the Otis system) was 78 deg.9' minus 54 deg.35', or 23 deg.34', the tangent of which equals 0.436. Forty-three percent of the unbalanced weight of the car and load would then have borne upon the, say, 12 sets of rollers on the curve. The immense frictional load thus added to the entire system would certainly have made it dismally inefficient, if not actually unworkable.

In spite of Eiffel's public remarks regarding the safety of the Roux machinery, in private he did not trouble to conceal his doubts. Otis' representative, Hall, discussing this toward the end of Brown's previously mentioned report, probably presented a fairly accurate picture of the situation. His comments were based on conversations with Eiffel and Koechlin:

Mr. Gibson, Mr. Hanning [who were other Otis employees] and myself
came to the unanimous conclusion that Mr. Eiffel had been forced to
order those other machines, from outside parties, against his own
judgment: and that he was very much in doubt as to their being a
practical success--and was, therefore, all the more anxious to put in
our machines (which he did have faith in) ... and if the others ate
up coal in proportions greatly in excess of ours, he would have it to
say ... "Gentlemen, these are my choice of elevators, those are yours
&c." There was a published interview ... in which Eiffel stated ...
that he was to meet some American gentlemen the following day, who
were to provide him with elevators--grand elevators, I think he
said....

The Roux and the Otis systems both drew their water supply from the same tanks; also, each system used similar distributing valves (fig. 32) operated from the cars. Although no reports have been found of actual controlled tests comparing the efficiencies of the Otis and Roux systems, a general quantitative comparison may be made from the balance figures given for each (p. 40), where it is seen that 2,665 pounds of excess tractive effort were allowed to overcome the friction of the Otis machinery against 13,856 pounds for the Roux.

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.

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.

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

Positive effect

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

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

Power: 156 p.s.i. x 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 x sin 54 deg.35' 11,500 lb.
Live load: 100 persons @150 lb. = 15,000 x sin 54 deg.35' 12,220
------ -- 23,720 lb.

Positive effect

Counterweight: 6,600 x sin 54 deg.35' 5,380

Power: 156 p.s.i. x 2 (pistons) x 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. x 2 (plungers) x 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)