In normal service, what should the black hand of the duplex air gauge read?

In normal service, the black hand of the duplex air gauge typically indicates the level of air pressure in the braking system of the train. A reading of 110 psi is generally standard for many railway systems, as it maintains effective braking performance while ensuring safety and operational efficiency.

This pressure provides a balance between sufficient force for braking and safety measures to prevent issues such as brake failure due to insufficient air. When the black hand reads 110 psi, it signifies that the air supply is at an adequate level for normal operation under typical conditions.

Other readings, such as 90 psi, may indicate lower pressure that can compromise braking performance. Similarly, 130 psi or 150 psi could suggest an excessive pressure that may lead to potential risks or operational inefficiencies, such as the risk of over-pressurization in the system. Thus, the correct value is crucial for maintaining the safety and functionality of the train's braking mechanism.