What does the red hand on the duplex air gauge indicate?

The red hand on the duplex air gauge is designed to indicate the pressure in the straight air pipe. This is crucial for train operations because the straight air pipe is primarily responsible for supplying the necessary air pressure to the brake cylinders, which in turn enables the train to decelerate or stop.

Monitoring the pressure in the straight air pipe is essential for ensuring that the braking system functions effectively. If the pressure in this line is too low, it could indicate a potential issue with the braking system, which might compromise the safety and performance of the train. Therefore, the presence of a clearly marked red hand for this specific pressure measurement allows train operators to quickly assess and respond to any anomalies in the braking pressure system.