Denny D’s Did You Know - Dynamic Brake Features

There are two important locomotive features regarding dynamic brakes that an engineer must be aware. Although this post is primarily for engineers, it may be helpful for a conductor to remember this in the future. On the train and to impress your FIT instructor. One is Dynamic Brake Interlock and the other Dynamic Brake Holding Feature. Both terms are found in the Air Brake and Handling Rules Glossary.


Dynamic Brake Interlock (DBI): A device that will automatically keep the locomotive brakes from applying when the automatic brakes are applied during dynamic braking. 


The system is designed to keep from sliding the locomotive wheels or applying too much braking force on the head end. 


There are two important things to keep in mind with DBI. 


First, it should never be relied upon to bail off the locomotive brakes automatically. There is a chance that the locomotive you are on or a trailing locomotive is not equipped with this feature or not working properly.


Second and most important, DBI does not prevent you from applying the locomotive brakes with independent brake handle when needed. If you are operating light power or with even just a few cars this is when it is important to remember what DBI does. If in dynamic brake and you need to place the train in emergency for whatever reason, the locomotive brakes will not apply. If you are light power, no brakes are being applied, or if you only have one or two cars, only the brakes on those cars are trying to stop you. In order to get the locomotive brakes to apply, you must move the independent brake handle. You may still need to bail off to keep from sliding the wheels. 


Dynamic Brake Holding Feature: A feature of the lead, controlling locomotive  that allows dynamic braking effort when a  PCS open condition exist.


When operating in power and an undesired emergency occurs, the PCS takes approximately 20 seconds to come on. This allows you gradually reduce the throttle to keep the slack stretched, preventing a break in two. When in dynamic brake, the dynamic brake holding feature allows dynamic braking even when the PCS comes on. This allows you to keep the slack bunched, preventing a possible break in two. In either case, remember to bail off. Also, while in dynamic brake, as speed and the power reduces you may need to slowly apply the independent brake while bailing off to keep the head end from rolling out. 



Keeping these two features in mind when operating in dynamic brakes is crucial to safe train operations.