What are indications of a main reservoir rupture on a PA5 train?

A main reservoir rupture on a PA5 train is characterized by a rapid decrease in main reservoir (MR) pressure due to the sudden loss of air that would normally be maintained in the reservoir. When there is a rupture, the system experiences a quick drop in air pressure, which can cause the air compressors to run continuously in an attempt to compensate for the loss. Observing MR pressure dropping below 95 psi is also a critical indicator, as this level signifies that the system is not maintaining sufficient pressure for proper operation.

This scenario provides a clear signal to engineers and operators that there is a serious issue that needs immediate attention. Other indicators, such as the constant operation of the air compressors, further emphasize the abnormality of the situation, as the compressors would typically not need to run continuously unless the system is struggling to maintain pressure.

While the other options mention symptoms related to pressure or alarms, they either suggest more gradual changes, which do not align with the immediate effects of a rupture, or indicate no significant pressure changes, which would not typically occur in a rupture scenario.