What happens if Brake Pipe pressure drops below 90 pounds on a PA4 train?

When the brake pipe pressure drops below 90 pounds on a PA4 train, it indicates an issue that can impact the operational safety of the train. In this scenario, the correct response is that motor power will be lost. This automatic response occurs as a safety measure to ensure that the train can no longer accelerate or maintain speed in an unsafe condition, hence helping to prevent potential accidents.

The loss of brake pipe pressure signifies that the braking system may not function as intended, which can create a hazardous situation. Consequently, to enhance safety, the system de-energizes the motors, effectively stopping the train or preventing it from gaining speed until the issue is rectified. This safety protocol helps ensure that the train remains under control and can be brought to a halt if necessary.

Understanding this mechanism is crucial for train engineers, as it underlines the importance of maintaining proper brake pipe pressure for the safe operation of the train’s electrical and traction systems.