The red hand of the duplex air gauge indicates the pressure in which reservoir?

The red hand of the duplex air gauge specifically indicates the pressure in the main reservoir. This reservoir is crucial for the operation of the train's air brake system, as it supplies the compressed air needed for brake application. Maintaining the proper pressure in the main reservoir ensures the effective functioning of the air brake system, allowing the train to stop safely and efficiently.

In the context of train operations, understanding the role of the main reservoir is vital. The main reservoir is typically the primary source of compressed air, and its pressure must be monitored closely to ensure that all braking systems have adequate air supply. Knowing the function of this gauge helps train operators make quick assessments regarding the air supply and can aid in making timely decisions if pressure drops below operational thresholds.