NEIEP Mechanics Practice Exam

How is the slow door driven in mechanically linked swing-arm door operating mechanisms with two speed doors?

1. By a motorized pulley system

2. Driven by a secondary link on the swing arm

3. By manual adjustment

4. Using a hydraulic mechanism

The correct answer is: Driven by a secondary link on the swing arm

In mechanically linked swing-arm door operating mechanisms featuring two-speed doors, the slow door is driven by a secondary link on the swing arm. This design allows for different speeds of door operation; when the swing arm is engaged, it transfers the motion effectively through this secondary link to control the slow door's movement. The arrangement enables the slow door to open or close at a reduced speed, enhancing safety and accessibility, especially in environments where a quicker operation could pose risks. The secondary link is crucial as it provides the necessary mechanical advantage and ensures that the movement of the slow door is coordinated with that of the fast door, maintaining an efficient operation of the overall system. Other methods, such as a motorized pulley system or hydraulic mechanisms, may play roles in different door operation designs, but in this specific system, the secondary link on the swing arm is what ensures the slow door is activated in harmony with the mechanism's overall function. Manual adjustment is not a viable method for controlling the automatic linkage required for two-speed doors, as this would negate the efficiency of the system.