During the charging procedure, when is it permissible to increase engine RPMs?

Increasing engine RPMs during the charging procedure is permissible when main reservoir pressure fails to stay above 10 psi. This practice is essential because maintaining adequate main reservoir pressure is critical for the proper operation of the air brake system. If the pressure drops below this threshold during the charging phase, it indicates that the system is not charging effectively and may require additional engine power to help build pressure more rapidly.

By increasing the engine RPMs, the air compressor is allowed to produce more air, which can help replenish the main reservoir and ensure that the train is adequately prepared for safe operation. It is crucial to monitor the pressure carefully to avoid operating with insufficient braking capability.

The context of the other choices helps clarify why they are not appropriate for increasing engine RPMs during the charging procedure. For example, increasing RPMs when the engine temperature is low may not directly relate to the immediate need for air pressure and could potentially harm the engine if not managed properly. Checking for leaks is a critical safety measure that typically requires the focus of the crew to ensure there are no potential failures in the system; increasing RPMs at this time would distract from that task. Lastly, while preparing for departure might create a need to build air pressure, it does not specifically address the urgent need for