Tension Sheave: Compensation Rope Tensioning, Slack-Rope Safety Switch and EN 81-20 Requirements

The tension sheave (also called compensation rope tension sheave or tail cord tensioner) is used in traction elevators with 2:1 roping or in high-rise applications using compensation ropes or chains. Functions: (1) Compensation rope tensioning — in high-rise elevators (typically travel >30 m), compensation ropes or chains hang below the car and counterweight to balance the varying weight of the suspension ropes; the tension sheave at the bottom of the hoistway keeps the compensation ropes taut; (2) Tail cord management — in older systems, a heavy weight (tension weight or 'socking') is attached to the tail cord loop; the tension sheave guides this loop; (3) Slack rope prevention — a slack-rope safety switch is typically integrated with the tension sheave assembly; if the rope slackens beyond the sheave's travel range, the switch opens the safety circuit. EN 81-20 specifies requirements for the tension sheave enclosure (guarding to prevent access), minimum sheave diameter (D/d ≥40 for wire ropes), and the slack-rope detection switch. In MRL elevators using flat polyurethane-coated steel belts (e.g. KONE EcoDisc or Otis Gen2), a belt tension monitoring device replaces the traditional tension sheave.

View All Terms