THE MODERN SKYSCRAPER 



hydraulic elevator is dependent upon water pressure 

 acting upon a piston in a closed cylinder. The power 

 derived from this action is utilized in various ways 

 to meet certain conditions. Thus the size and length 

 of the cylinder are dependent upon the size of the eleva- 

 tor, the length of the elevator shaft, and the amount 

 of water pressure available. Where economy of space 

 is necessary, short cylinders are used, in which the water 

 pressure may be seven or eight hundred pounds to the 

 square inch. By connecting these with several sets 

 of pulleys, or sheaves, even a very short cylinder may 

 be made to propel elevators in high buildings. Or 

 just the opposite conditions may prevail, long cylin- 

 ders and pistons being used to operate through rela- 

 tively long distances under low water pressure obtained 

 from the ordinary city main. But in any case the 

 hydraulic engine is single-acting in such elevators, the 

 weight of the car being utilized for the descent. 



A modification of this type of hydraulic elevator is 

 the " pulling plunger " elevator, in which the weight 

 of the piston is greater than the loaded car. In this 

 type of elevator the water is expelled as the car ascends, 

 driven out by the weight of the piston just reversing 

 the action of the ordinary hydraulic elevator the water 

 pressure being used to raise the piston and allow the 

 car to descend. 



There is still another class of hydraulic elevators, 

 known as the plunger, or direct-lift class, which in- 

 stead of being pulled upward by cables are pushed up 

 from below by a steel piston acting directly against the 

 base of the car. The length of this steel piston and 



