ELEVATOR (Lat. c/crator, raiser, from e/c rare, to raiser or LIFT. A meellanieal contriv ance for transporting passengers or freight be tween points at different levels. such as the sever al stories of a building. The modern high-speed passenger elevator is usually operated by hy or electric power, and it consists (1) of a rectangular car \chid] moves up and down be tween guides in a shaft or well, with doors open ing into earl floor, and (2) of the mechanism necessary to give this car its up and down move ment. Such elevators are usually designed to run at a maximum speed of from troll/ to sou feet per minute. but may be run at any less speed the operator may desire. Safety from accident is provided for in variou: ways. Brozolly •on sidered, modern elevator safety devices may be divided into two classes: (1) Clutch devices which are thrown into operation when the car exceeds a certain speed, and stop the ear by seiz ing hold of or. gripping guides fastened to the walls of the elevator shaft : and (2) air-cushion devices. whose purpose is to break the shoe!: of a falling ear so that injury will not result to its passengers. Elevator safety grips are of various forms, and the successful Ones are nearly all owned or controlled by firms which build ele vators.
The general principle upon which these devices operate is nearly the saint!. whatever their indi vidual forms may be. A governor is placed on the elevator car or on the beam which supports the sheaves. whose speed varies with the speed of the ear. When a certain speed is exceeded this governor actuates a mechanism which throws the clutch into operation, as is seen in the full. page illustration. The older and most commonly used form of air-cushion, invented by F. T. Elli thorpe. consists essentially of making the lower portion of the elevator shaft tight so that the ear falling into it acts as a piston in a cylinder and is brought to a slow stop by the compression of the confined air. In one of the largest in stallations of this form of eushion, the closed shaft begins at the third story. and is 50 feet deep. The total travel of the car is 287 feet, which makes the ratio of the depth of the air cushion to the distance of travel as 1 to 5.74.
In a display test which was made with the cush ion, a car weighing 2000 pounds was allowed • to drop the total 2S7 feet. and it came to a complete stop without breaking eggs and elec tric-light bulbs which were placed on the floor of the car. more recent form of air-cushion has the air-cushion at the top of the shaft. In this arrangement the car carries two grips, the jaws of which. in normal operation. encircle but slide loosely over two steel cables provided with buttons at intervals. These cables are attached at their tops to a yoke, which is carried by a pis ton-rod and piston working in a vertical steel cylinder placed on the roof of the shaft. Nor mally the piston is held at the top of the cylin der by a spring latch. \\ien the ear falls the governor first operates a clutch which opens this latch, and, secondly, it operates the grips which close on the button-ropes. This throws the weight of the ear into the yoke and piston. which. slid ing down in the cylinder. compresses the con tained air and brings the car to a gradual stop. The safety device is the most important appur tenance of the elevator ear: the car itself is of simple construction. consisting usually of a rev tangul:n• steel framework covered inside with a grillwork of metal and provided with a solid floor and roof attachments for the hoisting cable.
For high-speed passenger elevators the operat ing mechanism is usually hydraulic or electric. III hydraulic. elevators the hoisting cal des run from the top of the ear to and over sheaves at the top of the shaft, and thence to the operating machinery in the basement of the building. In the basement the cables pass around alternately fixed and traveling sheaves, the latter being at tacked to the piston-rod of the hydraulic cylin der. To raise the car the pressure is turned into the cylinder and forces out the piston-rod, thus pulling the traveling sheaves away from the fixed sheaves. The hydraulic cylinder is often placed in a vertical position, and the traveling sheaves move up and down in the same shaft as the car.