Page 5 - Brochure

TECHNICAL
Elevator Safety
Elevator bu ers are safety devices which are required to be mounted at the base of an elevator shaft. As with any safety device, elevator bu ers have to meet with a variety of specifications.
One of the most important of these specifications is the manner in which the bu ers must bring an impacting elevator car to rest. There are di erent technical specifications for elevator bu ers in di erent regions worldwide however all employ the same basic performance criteria.
Since the very early days of elevators, a variety of safety systems have been employed to ensure that the elevator will not free fall. The purpose of elevator bu ers is to provide protection against the malfunction of an elevator control system resulting in the elevator continuing to travel past the lowest stop to the base of the elevator shaft. The bu ers are specified in accordance with the operating velocity and mass of the elevator.
Although freefall is not a realistic event for an elevator, the specification and code requirements are based on the assumption of freefall.
The requirement for elevator bu ers fall into two categories depending on the type of bu er.
1. Energyaccumulationbu ers:Thesecantaketheform of simple mechanical springs or polymer bu ers which store the absorbed energy of the impact in the form of strain energy. In some accumulation bu ers this stored energy can be dissipated on the return movement of the bu er leading to two separate requirements:
a) Bu erswithlinearandnonlinear characteristics – these can be used if the elevator does not exceed 1.0m/s.
b) Bu erswithbu eredreturnmovement–thesecan be used for elevators that do not exceed 1.6m/s.
2. Energy dissipation bu ers: These are usually hydraulic bu ers which dissipate the energy of the impact in the form of heat during the travel of the bu er. This type of bu er can be used for all rated speeds, but must be used for speeds of 1.6m/s or over.
BUFFER PERFORMANCE CRITERIA – ENERGY DISSIPATION BUFFERS
Performance criteria in all specifications is governed by 2 underlying rules which state that the buffer must arrest a freefalling mass travelling at 115% of the rated speed of the elevator:
(i) With an average deceleration not exceeding 1g.
(ii) Without exceeding a deceleration of 2.5g for a time period greater than 0.04 seconds.
In addition a further, but separate, requirement states that the buffer stroke must be at least as great as free fall distance required to reach 115% of the rated elevator velocity. It is this requirement that dictates the stroke and consequently the installation height of elevator buffers. Due to customer demands, most elevator buffers do not deviate far from the minimum stroke requirement.
THE BURJ KHALIFA TOWERS OVER DOWNTOWN DUBAI
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