Elevator Mechanic Practice Exam

There is a noise coming from a freight door. The sheave is moving, but the chain is not. What is the problem?

1. Excessive tension in the door’s springs

2. Misalignment of the sheave

3. Oil on the drive chain

4. Weakening of the chain’s metal

The correct answer is: Oil on the drive chain

The correct reasoning for identifying the problem lies in the relationship between the sheave and the chain. When the sheave is moving but the chain is not, it can indicate that there is insufficient friction for the chain to engage or that it is not functioning properly. If there is oil on the drive chain, it can create a slippery surface. This reduces the friction required for the chain to grip the sheave effectively and function as intended. Consequently, while the sheave attempts to turn, the chain remains stationary due to this lack of engagement caused by the lubricated surfaces. This scenario emphasizes the importance of maintaining a clean drive chain to ensure proper operation. Other possibilities like excessive tension in the door’s springs or misalignment of the sheave might lead to different operational issues, such as strain or binding rather than a lack of movement of the chain despite the sheave's motion. Weakening of the chain’s metal might lead to different symptoms, often characterized by the chain not being able to hold tension or breaking rather than simply not moving. Thus, the presence of oil on the drive chain is the most plausible cause for the observed problem.