WHY DOESN´T AN ELEVATOR

FALL OUT OF CONTROL?

Nivel: intermedio/avanzado

By Luis Fernando Carvajal

The safety of any kind of transport medium is very important. An elevator can be considered as a form of transport inside a building. I think it is good to know how it works before explaining why it doesn´t fall out of control.

Photo: New York Marriott Marquis Hotel

An elevator is a cabin. It moves along rails on wheels like a train. The cabin is hung by cables from a pulley at the top of the building.

One end of the cable is attached to the cabin and supports it. The other end is attached to a counterweight. The counterweight is 50% heavier than the weight of the cabin plus the maximum number of people contained in it.

There is an engine connected to the pulley by a shaft. When the elevator is required to go up or down, the engine transmits the movement to the pulley, and so to the cabin.

THREE CONTROLS ON AN ELEVATOR

Basically, there are three mechanisms for making sure that an elevator doesn´t fall out of control.

The first one is that the elevator engine has an emergency electronic device. This works when the weight of the cabin and the people in it is higher than the cabin capacity, when this happens the engine doesn´t start and the elevator stays motionless. Obviously, in this case there is no danger to anybody.

A second system is designed to prevent high speeds. This means that the elevator is not permitted to go fast. It consists of an independent pulley-cable mechanism. When the velocity of the elevator is greater than 25% over the maximum velocity, this system automatically stops the elevator.

The last system is controlled by the minimum stress on the cable. This stress must be at least equal to the weight of the cabin. If the cable breaks away suddenly, there is no stress on the cable, so an automatic control shoots out a group of steel wedges. These are jammed between the rails and the wheels making it physically impossible for the cabin to move.

Foto: stallionsecurity.com

QUESTIONS:

1. In what way is the operation of an elevator like a train?

2. Where is the pulley located?

3. The cable is attached to a counterweight and - what?

4. Add the missing word. The shaft connects the engine to the …....................

5. What does the engine transmit to the pulley?

6. How many systems are there to make sure the elevator doesn’t fall?

7. Only one of these statements is TRUE:

a) the first mechanism is mechanic

b) the first mechanism is operated by a man

c) the first mechanism is defective

d) the first mechanism is an electronic device

8. What is the second system that prevents excessive speed?

9. What is the minimum stress on the cable of an elevator?

10. When the steel wedges shoot out, where do they go?

ANSWERS:

1. It has wheels and runs on rails.

2. At the top of the building.

3. The cabin.

4. pulley

5. movement

6. three

7. d)

8. independent pulley-shaft mechanism.

9. at least the weight of the cabin.

10. between the wheels and the rails.