What two pressures does the duplex air pressure gauge monitor in the engineer's cab?

The duplex air pressure gauge is an essential instrument located in the engineer's cab that provides vital information about the air brake system's performance and status. It specifically monitors brake pipe pressure and brake cylinder pressure.

Brake pipe pressure refers to the pressure within the main air brake line, which is responsible for transmitting the air signal throughout the train. This pressure is crucial for the functioning of the air brakes, as it enables the modulation of the brake system based on the demands for braking.

Brake cylinder pressure, on the other hand, indicates the pressure applied directly to the brake cylinders themselves. This pressure is responsible for actually engaging the brakes of each car in the train. Monitoring the brake cylinder pressure allows engineers to understand how effectively the brakes are engaging, which is critical for maintaining control and safety during operation.

By tracking both of these pressures, the engineer can make informed decisions about braking, ensuring the proper functioning of the air brake system and enhancing the overall safety of train operations. Both pressures are integral to the effective performance of air brakes, which is why this option accurately reflects the function of the duplex air pressure gauge.