An idler or deflection pulley that re-routes hoist ropes to achieve the required roping configuration.
Full Definition
An elevator secondary sheave (also called a deflection sheave or diverter pulley) is a grooved wheel mounted in the machine room or overhead structure that redirects hoist ropes from the drive (traction) sheave to the car or counterweight, allowing configurations that would otherwise be geometrically impossible given the spatial relationship between the machine, car, and counterweight. Secondary sheaves are essential in side-drive machine room-less (MRL) installations and 2:1 roping systems. Unlike the traction sheave, the secondary sheave does not transmit torque; its sole function is to change rope direction with minimum friction. The sheave is carried on anti-friction (ball or roller) bearings and its groove profile must match the rope diameter — typically an undercut U-groove for steel wire ropes — to prevent rope deformation. EN 81-20 clause 5.5.5 specifies minimum sheave diameter ratios relative to rope diameter (D/d ≥ 40 for traction sheaves and ≥ 25 for secondary sheaves with a single layer of rope). Sheave groove wear is assessed by profilometer or template gauge; grooves that have worn more than 10 % of the original depth or developed sharp edges must be re-machined or the sheave replaced. Bearing clearance and lubrication are checked at each maintenance visit.
