Buffers in Elevators

1. Spring (mechanical, linear) buffers : Spring buffers prevent the bottom of the cabin from crashing hard on the floor. The spring-loaded buffers meet the kinetic energy of the car, loaded car or counterweight in a spring-loaded configuration. They are buffers of the energy storage type. Stroke distances can not be less than 65 mm.
2. Polyurethane (mechanical, nonlinear) buffers : As can be inferred from its name, this buffer is made of some type of elastic, cellular elastomer polyurethane. It consists of organic molecular chains that come together through its chemical structure. If more than one buffer is to be used (depending on the elevator load), these buffers must be same kind, height and placed equally on the same level. Over the past 20 years, energy-storing buffers made from special polyurethane materials have been used at speeds up to 1 mps but cannot perform adequate damping for higher speeds. Companies in this field are working intensively to improve performance.
3. Hydraulic buffers: Energy-wasting hydraulic buffer absorbs the kinetic energy of the loaded cabin or counterweight, and after impact is automatically reset when the cabin is lifted off of it. The hydraulic level of these buffers must be easily controllable. Such buffers can be used in any speed group, and must have a safety switch.

According to the standards, elevators with a speed of more than 1 mps are only allowed to use energy-efficient, hydraulic buffers.

The energy-saving type of hydraulic buffers are expected to include:

• An average braking acceleration during tamping that does not exceed 1 g-force while the rated load is reduced by 115% of the predicted speed of the loaded car.
• The duration of the large braking torque g-force of 2.5 must not exceed 0.04 seconds. (The braking accelerations above 1 g-force are considered disturbing to humans, while the braking acceleration of 3 g-force is regarded as dangerous for human safety and health.)
• There must not be a permanent deforming in the buffer after impact.

Briefly referring to the installation of the buffers: If the buffers are securely fixed to the bottom of the car frame, there must be an area under the buffers that will form a safety zone of a  70-by-100 cm, and 50 cm high (Figure 1), allowing space for a person in the lying-down position. Even in a fall to the bottom of the shaft, there should be space for someone to take shelter. In cases where the shaft cavity cannot meet the , collapsible buffers with platform or special solutions, as cited in risk analysis reports, should be used. (The shelter area in the upper space should be a  50-by-70 cm, 100 cm high.)

From the general characteristics of buffers and general information on the usage figures, let’s see the standards: Elevator buffers must be manufactured with EN 81-20/50 standards. European standards indicate that qualifications should be kept at the highest level. The buffers should be inspected in the elevator shaft at intervals of six months, and the oil level should be checked in hydraulic buffers to see if any damage has occurred or if the condition has deteriorated.

According to the latest revision EN 81-20/50, non-linear and energy-wasting type buffers shall contain non-removable information label with type name, type certificate number, buffer type, hydraulic buffer oil type, manufacturer’s name, stroke distance, max speed, max capacity, and postal address (for example, a riveted metal label). There should also be a product manual onsite, printed in at least one language: the language of the manufacturer who produced it and/or in the most widely used language in the European Union.

Elevators should not be used without buffers, and maintenance of buffers should be tightly monitored.