What position will the force draft blower final control element fail to if control air is lost?

When control air is lost to the force draft blower final control element, the system will default to a position that is safe and manageable to protect the equipment and maintain some level of operational integrity. In this case, the correct outcome is that it will fail to the minimum position, which is important for several reasons.

Failing to the minimum position allows the draft blower to maintain a baseline airflow. This is crucial because it helps prevent the buildup of dangerous gases and maintains some level of combustion stability within the system. If the blower were to fail to a full or optimal position without control, it might lead to an unsafe situation, such as excessive air distribution that could disrupt the combustion process or damage other equipment.

By defaulting to the minimum position, the system ensures that there is still some draft present, which is necessary to prevent back pressure and to allow for safe operation until control air is restored or manual intervention is possible. Thus, understanding the role of the final control element in airflow management highlights why the minimum position is the correct answer in the context of loss of control air.