Diameter allowed for sheaves and drums.

• A. Platform Leveling
• B. Pitch Diameter
• C. Hydraulic Driving Machines
• D. Emergency Personnel Access

Answer: (B)

Pitch diameter is the key diameter for sheaves and drums because the belt engages along its pitch line. In escalator and moving-walk drives, the belt’s speed and the drive ratio depend on the diameter of the circle where the belt’s pitch sits—this is the pitch diameter. The actual outer diameter or other physical measurements aren’t what set the belt speed or the gear ratio; those other dimensions include addendum, belt thickness, or wear, and don’t govern the belt’s engagement. So choosing the pitch diameter lets you correctly analyze speed, tension, and length in the drive system. The other terms refer to safety, layout, or drive components unrelated to how belt drive performance is determined.