Part 6

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:

Translated from Jean A. Keim, La Tour Eiffel, Paris, 1950.

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.

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.

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.

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.

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.

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

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.