HYDRAULIC ELEVATORS
The same principle is used in hydraulic elevators. The hydraulic cylinder lies horizontally on the basement floor and by means of pulley gearing a short motion of the plunger is sufficient to raise the car several stories.
In a more modern type of elevator the plunger acts directly on the car. The plunger is long enough to reach to the top story of the building which means that it must sink far into the ground in order to let the car down to the first story or basement. A steel pipe is sunk into the ground and serves as the cylinder and in this the long plunger operates. In one of New York’s tall buildings the cars are lifted to a height of 282 feet. The plungers are 6½ inches in diameter and they travel at a speed of over 400 feet per minute. The car which, when loaded, weighs 1,617 pounds, is supported on the top of the plunger. However, counterweights are provided which balance the weight of the car, so that practically the only weight lifted by the plunger is that of the passengers. The advantage of this type of elevator is that it reduces the danger of accident. The motion of the car is steady and easily controlled. The car cannot move down above a given speed and the only possible danger is that the plunger might break. However, a shaft of steel 6½ inches in diameter, even if hollow, is hardly likely to give way even under the most extraordinary loads to which it might be subjected in elevator service.