What is the brake pipe reduction required for a full service brake application at a charge of 90 psi?

For a full service brake application at a charge of 90 psi, the typical brake pipe reduction required is indeed 26 psi. This reduction is significant because it ensures that enough pressure is released from the brake pipe to initiate a proper braking response throughout the entire train.

The function of the brake pipe in a train's air brake system is to transmit the compressed air necessary for brake applications. When the engineer makes a full service application, a decrease in the brake pipe pressure activates the brake valves on individual cars, resulting in coordinated braking action across the entire train length.

The 26 psi reduction is part of standard practices in train handling, allowing for effective and safe stopping distances without overshooting or causing excessive wear on the braking system. Other listed reductions of 20 psi, 15 psi, or 30 psi do not align with standard operational procedures for a full service brake application at this specific charge of 90 psi, confirming that 26 psi is the correct and necessary reduction to achieve the desired braking performance.