Poor rope tension is a common defect that we see during a maintenance audit or site survey. This is most disconcerting as explained below.
For various reasons there is more than one suspension rope on a lift. The main reason is that if there was only one rope and it broke it would be a catastrophic failure and as such would be a notified incident.
It is extremely important to ensure that all the suspension ropes have the same tension before the lift enters service and during the course of the suspension rope’s life. On a traction lift the hoist ropes are hung on a driving sheave which is rotated by various means. It is important that all ropes driven by a traction sheave travel the same distance. It is equally important that the ropes have the same characteristics. The ropes on either side of the drive sheave must be checked individually because the rope tensions on the counterweight side will be different to the ropes on the lift car side.
As an example, if we look at the ropes on the car side of the traction sheave and the tensions were unequal then the loads in each rope must be unequal, their respective diameters will therefore be different. The ropes which start off with the lightest loads will want to travel greater distances than those ropes with heavier loads as the traction sheave rotates and will rapidly get pulled into the traction sheave groove as the load increases. These ropes are then forced to slip in the groove of the traction sheave. Rapid wear will take place on both rope and traction sheave; as the ropes are forced to slip. The driving sheave grooves will also change shape and traction may become a problem.
A loss of traction due to worn ropes and traction sheaves cannot be tolerated. Therefore it is paramount that the tensions of all ropes where they terminate is carried out on a regular basis during routine maintenance to avoid costly repairs.
