PILOT VALVE 



Wafer 



under 



pressure 



' Control cable 



Water under 



^"" 



MAIN VALVE 



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 Metres, 

 Paris, 1900, p. 130.) 



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.'^ In making the upward or down- 



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 

 thiseffect diminished, but as the rams moved back into the cyl- 

 inders their unsupported length was correspondingly reduced. 



ward 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 ele- 

 vator 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 



PAPER 19: ELEV.A.TOR SYSTEMS OF THE EIFFEL TOWER 



33 



