What is the function of an idler in a chain drive?

• A. A sprocket that increases torque.
• B. An idle sprocket or guide that maintains tension and guides chain to proper path.
• C. A device that stores energy.
• D. A pulley with no role in belt tension.

Answer: (B)

An idler in a chain drive acts as a non-driven sprocket or pulley that creates the proper path for the chain and takes up slack. Its main job is to keep the chain taut enough to stay engaged with the drive and driven sprockets and to guide it along the correct route, preventing sag, misalignment, or derailment. It doesn’t increase torque (that comes from the driving sprocket and the load), and it isn’t a device that stores energy. It’s specifically there to maintain tension and ensure the chain follows the intended path.