What is the elevator design for safety?

What is the elevator design for safety?

This content is the fifth section of the traction elevator system introduction. Except for the protection related to overspeed, most of the content is also applicable to other types of elevators, home lifts and residential lifts

5. Safety protection system (traction elevators)

In the event of an abnormality in the elevator, the elevator can be stopped to prevent damage to passengers.

The safety protection system consists of 8 parts:

a, Overspeed protection device

Including speed governor, safety gear and governor tension wheel.

The speed governor is a device that can detect the overspeed of the elevator.

The speed governor, governor tension wheel and safety gear are respectively installed on the top of the guide rail, the low end of the guide rail and the car. The three are connected by a rope to achieve simultaneous movement and synchronous speed.

When the car overspeeds, the speed governor throwing block extends out by centrifugal force, which drives the locking mechanism to lock the speed governor, which simultaneously  pulls the safety gear on the car so that the safety gear wedges in and clamps the guide rail to stop the car.

Common faults include: the electrical switch of the speed governor fails, the action of the mechanical device is unreliable, and the car cannot be stopped after the safety gear acts. These faults can disturb the overspeed elevator from being reliably stopped.

b, Anti-overtravel protection.

The upper and lower stations of the elevator shaft are equipped with anti-overtravel protection devices.

Anti-overtravel protection includes forced speed change switch, pre-final switch, final switch.

The function of the forced speed change switch is to make the elevator start to decelerate before reaching the destination floor, and can stop smoothly when it reaches the leveling position. 

The function of the pre-final switch is to stop and brake the traction machine immediately through the control system when the car exceeds the top or bottom leveling position. 

The function of the final switch is that when the elevator cannot stop running after the pre-final switch is activated, the final switch will be triggered and the safety circuit will be cut off. Cut off the power supply to the traction machine and the brake to stop the elevator.

Once these devices fail, the elevator will have a squatting or topping accident.

c, Buffers

Buffers are installed in the shaft pit. Buffers are categorized into energy storage type and energy consumption type. 

Its function is to absorb and consume kinetic energy and potential energy when the car or counterweight falls out of control, so as to reduce losses and injuries as much as possible. Polyurethane buffers will be weathered or damaged after a long term. The common failures of energy-consuming buffers are lack of oil in hydraulic devices and corrosion of plungers. Both of these failures will cause the buffer to lose its function of buffering and decelerating.

d, Protection against personnel shearing and falling.

Including toe guards, door panels, door locks, door locking and closure verification devices. These devices effectively protect passengers from shear injuries from elevator mechanical parts.

e, Phone and alarm 

An alarm device needs to be installed in each elevator car. When passengers are trapped in the car, even in the state of power failure, they can contact the operator of the elevator company to organize rescue in time. The traditional way of communication is through land telephone lines. Now the popularization and promotion of the NBN network makes wireless communication a good alternative product.

f. Rescue device

Including brake release wrench, turning handwheel, electric rescue device. When the elevator fails and traps people, rescuers can move the elevator car to the leveling position through the rescue device. Now the adoption of electric brake-release is getting popular but the traditional mechanism is always a reliable backup.

g, Protection against mechanical damage

Includes traction sheave guard, sheave guard, speed governor guard, car return sheave guard, counterweight return sheave guard, speed governor tensioner guard, counterweight guardrail, etc. Various protective covers can effectively prevent workers from being accidentally involved by moving parts.

h. Electrical safety protection device

There are many electrical safety protection devices in elevators, such as emergency stop buttons, speed governor switch, cranking handwheel switch, speed governor rope slack switch, buffer switch, safety gear switch, etc. After any safety protection switch action, the elevator should stop running immediately.

The above is the composition and function of the traction elevator safety protection system. Only if lift installation and lift maintenance are carried out in strict accordance with regulations, the risk of personal injury can be effectively reduced.

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