Elevator
a moving platform or cage in a building, for carrying passengers or freight up and down. Vitruvius, an architect of Rome about 26 B. c., describes in his writings an apparatus built by Archimedes in the year 236 в. c., for lifting very heavy weights. vator consisted of a cast-iron screw extending the total height of the building. The car was built around the screw, the rotation of which caused the car to move either up or down.
The first elevator to be operated successfully by direct electric power, was designed and installed by the Otis Brothers' Company in the Demarest Building, New York City, during the year 1889.
The modern electric high-speed gearless traction elevator was developed by the Otis Elevator Company, in 1904, the first installation of this type being in the New York Edison Company's Building, New York.
Elevators may be divided into five general classes: electric, hydraulic, steam, belt, and hand power, to which may be added the escalator or moving stairway.
Electric elevators, constituting about 90 ELEVATOR per cent. of the installations of the pres- ent time, are of two types, namely, those with winding drums and those with traction sheaves. The former type are designed with drums spirally grooved on which the cables wind and unwind in CAR OIL BUFFER ← DRIVING SHEAVE IDLER SHEAVE IDLER SHEAVE JOLER SHEAVE ELEVATOR a which the cables pass, the friction between the sheave and the cables being the usual arrangement of car, counterbalance cables, etc., for an electric drum machine, while Figure 2 shows similar arrangement for the traction used until the advent of the high-speed drum machine was almost universally used until the advent of the high-speed gearless traction machine which was designed to eliminate the excessive drum sizes required for tall buildings. The been developed to cover the field of the elevator machinery may be located either at the base of the hatchway or over the top of the hatchway, the latter fies the arrangement.
There are three principal types of hy- There are three principal types of hydraulic elevators: the vertical, the horivertical and the horizontal types consist vertical and the horizontal types consist of a cylinder with piston rods connected to traveling sheaves, around which pass the cables which are attached to the car. under pressure, the piston is caused to move and the car raised. To lower the car, the water is allowed to discharge from the cylinder, the weight of the car being sufficient to overcome the friction of the water through the valves, pipes, etc.
The plunger elevator consists of a tube sunk in the ground a distance equal to the rise of the elevator and a plunger attached to the bottom of the car working in this tube through a stuffing box. Movement of the car is accomplished by COUNTER water under pressure entering the cylin- WEIGHT der, causing the plunger and the car to rise. To lower the car the water is allowed to discharge from the cylinder.
Except in special cases, very few hydraulic elevators are being installed at the present time, the cost of installation and also the cost of operation being much higher than for the electric type of elevator.
OIL BUFFER GEARLESS TRACTION ELEVATOR GEARLESS TRACTION ELEVATOR vators of the traction type are provided with straight grooved sheaves over The steam type of elevator consists of a steam engine as the motive power, the cables to the car pass. This type of elevator is practically obsolete at the present time.
The belt elevator is usually driven from a line shaft and is only used for The belt elevator is usually driven slow speeds.
The hand power elevator is used only expense of installing a power-driven elevator is not warranted. It is oper- ELEVATOR ated by pulling an endless rope over a driving sheave which is geared to the winding machine.
Safety features of elevator. - With the exception of the plunger type of elevator, practically all elevators are provided with what is known as a Safety Device, designed to grip the guide rails and stop COUNTER WEIGHT OIL BUFFER OIL BUFFER DRIVING SHEAVE JDLER SHEAVE CAR ROPING FOR GEARLESS TRACTION ELEVATOR the car if for any reason the speed of the elevator becomes excessive or if, due to the breaking of the lifting cables, the car starts to fall. Additional safeties are provided to automatically stop the car at the upper and lower terminal landings in case the operator neglects to ELGAR do so, and if the car runs by these landings, to cut off the supply of current, apply the brake, and bring the car to rest.
In connection with high-speed traction elevators, the gearless type of which is used for passenger service in the modern office buildings of our large cities, it is usual to provide oil-cushion buffers under the car and under the counterweight. If, due to accident, the car runs past the upper or lower landings, these buffers are compressed, bringing the car gradually to rest and at the same time reducing the traction between the lifting cables and the driving sheave. This is a very important safety feature as it prevents any further travel of the car or the counter-weight.
Taking the borough of Manhattan in the city of New York as an example, more than double the number of passengers are carried vertically in elevators than are carried by the surface, subway, and elevated lines combined, while the percentage of accidents to passengers traveling in elevators is very much less.
This is due to the exceptional safety features provided in connection with passenger elevators.