An escalator is a mechanized moving stairway, common in places with a lot of foot traffic or where a conventional staircase would be very long and tiring to climb. Escalators can often be seen in shopping malls , museums, multi-story parking garages, and subway stations, for example. Escalators are often installed in pairs, with an up escalator and a down escalator adjacent to each other, while a single escalator may be changed to go up or down according to the direction of heavier traffic at different times of the day.
An escalator is similar to a conveyor belt , but differs in that it is on an incline and has a surface of stairs rather than a flat belt. Most escalators also include a handrail that moves in conjunction with the stairs. To move from one end of an escalator to the other, a person may simply stand on one step until one reaches the end, or one may climb or descend the escalator like conventional stairs. Many escalators in busy areas are wide enough to accommodate two columns of people, and those who wish to stand conventionally remain on one side of the escalator
Escalators, while rather expensive and large, are actually relatively basic machines. The machinery of an escalator is hidden beneath its steps in what is called a truss . At the top of the escalator , housed in the truss, is an electric motor which runs the four gears that all escalators have - two drive gears on either side at the top and two return gears on either side at the bottom. These gears have chains that loop around the gears and run down each side of the escalator . Connected to each step, these chains help the steps make their way up, or down, the escalator .
The handrails that riders use for balance and safety on their ride up or down escalators are powered by the same system that powers the steps. The handrails are essentially long rubber loops connected to the two drive gears at the top of the escalator and powered by the same electric motor that powers the steps
Speed is controlled by a governor, similar in general principle to that used on stationary steam engines. Two heavy metal balls are attached to pivoted levers which are in turn fixed to a vertical shaft, revolving through gearing. The faster the shaft revolves, the more are the metal balls swung out by centrifugal force, and should the lift speed exceed a predetermined figure the governor actuates a brake