the general distribution of the city. Large establishments,
hotels or business houses, commonly have their own source of
energy, an electric or other power “plant,” on the premises.
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| Fig. 1.—The Plunger, or Direct Lift Hydraulic Engine. |
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| Fig. 2.—The Otis Standard Hydraulic Passenger Lift, with Pilot Valve and Lever-operating Device. |
The hydraulic elevator is the simplest in construction of elevators proper, sometimes consisting merely of a long pipe set deeply in the ground under the cage and containing a correspondingly long plunger, which rises and falls as required and carries the elevator-cage on its upper Construc-tion of elevators. end (fig. 1). The “stroke” is thus necessarily equal to the height traversed by the cage, with some surplus to keep the plunger steady within its guiding-pipe. The pipe or pump chamber has a length exceeding the maximum rise and fall of the plunger, and must be strong enough to sustain safely the heavy hydraulic pressures needed to raise plunger and cage with load. The power is usually supplied by a steam pump (occasionally by a hydraulic motor), which forces water into the chamber of the great pipe as the elevator rises, a waste-cock drawing off the liquid in the process of lowering the cage. A single handle within the cage generally serves to apply the pressure when raising, and to reduce it when lowering the load. The most common form of hydraulic elevator, for important work and under usual conditions of operation, as in cities, consists of a suspended cage, carried by a tackle, the running part of which
