When applying or reapplying brakes, what is the required brake pipe reduction for a fully charged system?

The required brake pipe reduction for a fully charged system is at least 6 psi. This reduction is critical because it ensures that there is sufficient pressure differential that allows for the required amount of brake application across the entire train. When the brake pipe pressure is reduced by at least this amount, it prompts the brake control valves in the freight cars to respond appropriately, thereby allowing for effective braking.

Using a 6 psi reduction helps initiate a smooth and controlled application of the brakes, ensuring that all the cars in the train engage their brakes simultaneously as intended. This reduction is aimed at achieving a quick and uniform braking effect, which is vital for maintaining stability and control during train operations.

In contrast, lower reductions might not create enough pressure differential for the brakes to engage properly, potentially leading to inefficient braking and safety concerns. Maintaining current brake pipe settings would not apply any brakes and could result in a lack of control when slowing or stopping the train.