What is the maximum train speed when operating with retaining valves set?

The maximum train speed when operating with retaining valves set is 15 MPH. This is established due to the design and functionality of the retaining valves, which are primarily used to maintain air brake pressure in the end of a train during certain braking situations, such as when descending a grade.

Operating at a reduced speed with the retaining valves set is crucial for maintaining overall train handling and safety. Higher speeds could lead to challenges in braking performance, as the retaining valves alter the brake system dynamics. Thus, adhering to the 15 MPH limit ensures that the train remains controllable and reduces the risk of brake system failure or issues that could arise from excessive speed.

This limitation is based on both safety protocols and mechanical considerations inherent in the operation of trains with retaining valves active. Understanding this speed restriction is vital for safe train handling and effective use of the air brake system.