A
lift is a transportation device that carries people
and freight to any floor of a building. A person
brings a lift to a certain floor by pushing a
button in the wall outside. The lift doors open
automatically after the car arrives at the floor,
and they close after the passenger has entered.
The passenger pushes the appropriate button to
indicate the floor where he or she wants the lift
to stop.
Most lifts in buildings of ten
or more floors are powered by electric traction
systems and are lifted by steel cables. There
are two types of electric traction lifts, gearless
traction and geared traction.
Gearless traction lifts are the
most commonly used. They travel at speeds of 120
to 600 metres per minute. Cables called hoisting
ropes lift the car. One end of each cable is attached
to the top of the car. The other end is connected
to a heavy steel counterweight that balances the
weight of the car and about half of its maximum
passenger load. The counterweight reduces to minimum
the power needed to operate the lift. The hoisting
ropes fit arount a pulley that is connected directly
to an electric motor. As the pulley turns, the
ropes move and the car goes up or down. A brake
holds the car in place when the lift stops.
NOTE: The tallest skyscraper
in the world, the Sears Tower in Chicago, U.S.A.,
has 103 lifts and 18 escalators! |
