If operating on a mountain grade, what should the regulating valve on the controlling locomotive be set to?

In mountain grade operations, the setting of the regulating valve on the controlling locomotive is critical for ensuring safe and efficient train handling. A setting of 90 psi is often recommended as it provides a balance between applying sufficient braking force while also avoiding unnecessary strain on the braking system given the steep grades. This pressure helps to maintain adequate braking response and control, especially when descending or ascending grades, where the dynamics of the train can change rapidly due to the incline.

Higher settings could lead to excessive braking force, increasing the risk of overheating the brakes or causing them to fail, whereas lower settings may not provide enough braking power, especially if the train is loaded or encountering steep slopes. Therefore, 90 psi is generally considered optimal for maintaining a safe operational average on mountainous terrain, giving the engineer an adequate buffer for managing their brakes effectively in various situational challenges presented by the grade.