Crash to the top

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Crash upwards is a technical term used in connection with traction sheave elevators for forms of technical failure of the elevator system in which the elevator car is accelerated upwards in an uncontrolled manner by the counterweight.

root cause

Traction sheave elevators are one of the most common elevator types and are used particularly for high conveying heights of over 30 m. In this design, the suspension elements are guided from the car via a traction sheave to a counterweight. The counterweight is usually just as heavy as the half-payload car. If the brakes fail, the gearbox is damaged, the drive pulley shaft breaks or the brakes are manually released (e.g. to free people), the lighter car will be pulled upwards by the heavier counterweight.

consequences

Depending on the type of elevator, the fault, the weight difference and the route to the shaft ceiling, high speeds can be achieved. If it hits the shaft ceiling, serious damage to the elevator and the building structure can occur. If there are people in the cabin, there is a risk of serious injury for them.

Risk assessment

The risk of falling down is very low with elevators. If the deviation from the nominal speed is too great, the speed limiter normally triggers the safety gear and stops the car within a short time. This safety function is also checked in Germany during the general inspection that takes place every two years .

However, the risk of a crash to the top has increased significantly in recent years. Until the 1990s, worm gears were mainly used, with which, due to the high level of self-locking, the risk of falling upwards was very low. With the planetary gears or gearless drives used today, however, there is practically no self-locking.

Countermeasures

There are several solutions, some of which can be retrofitted, to avoid falling upwards:

  1. a traction sheave brake is connected directly to the traction sheave and brakes the elevator in the event of an uncontrolled movement
  2. a dual-circuit brake consisting of two independent brakes which, depending on the type, are attached directly to the motor or the traction sheave. This solution is only used with gearless direct drives
  3. Catch upwards analogous to the catch device for the fall downwards.

Standards / regulations