Engineers and architects can now build
monumental skyscrapers towering over hundreds of feet in the air. However,
the
giants need some technological innovations in order to make it feasible for
people to work or live in them.
Imagine what life would be like without the aid of the lift if you worked on
the top floor of a skyscraper -- it would be miserable and weary.
The 2 most common designs of elevators nowadays are: hydraulic elevators
and roped elevators.
The Hydraulic Lift: Powered by Fluid
Pressure
The hydraulic lift is driven by a device called the hydraulic ram
(a fluid-driven piston mounted inside a cylinder). While the roped lift is
moved
by traction steel ropes (cables attached to the roof), rather than pushed
from below. Both kinds of elevators have built-in weight sensors that means
that the car will not move if it is over-loaded. To raise the car, the control system switches on the pump of the
tank. When the valve is closed, the fluid is forced to the cylinder. As
the fluid pressure increases in the cylinder, it would force the piston up
(attached to the lift). To lower the car, the control system sends a signal
to
open the valve. The fluid from the cylinder flows to the tank again, and as
the fluid pressure in the cylinder decreases, the piston lowers.
Roped
Elevators: Powered by pulleys
An
electric motor switches on the pulley system, raising and lowering the car
along guided rails. At the end of the cable is the counterweight. It moves
up when the lift lowers and moves down when the lift rises. It counteracts
with the potential energy of the car in order to conserve energy (the car
has to work against the friction). Unlike the Hollywood action movies,
real-life elevator cables will not snap into two, as they possess a safety
system (built-in brakes
that will grip on the cable when the car is over-speed). The system is activated by
a governor, which is a rounded device built around a sheath, positioned at
the top of the lift shaft. There are 2 hooked flyweights (weighted metal arms) held down by a
high tension spring fitted around the shealth. If the governor rotates
fast
enough, for the centripetal force (the force acting towards the centre) to
overcome the tension of the spring, the flyweight would be released, and the
hooks of the flyweights would catch the ratches mounted on the stationary
ratchet. This would halt the lift to a stop.
