What is the expected braking outcome when a 70-psi brake pipe reduction is performed?

What is the expected braking outcome when a 70-psi brake pipe reduction is performed?

• A. The train brakes will release
• B. A light brake application only on the front locomotive
• C. No braking effect
• D. An immediate brake application across the train

Answer: (D)

In a train’s air brake system, brake pipe pressure acts as the control signal for braking. When the pressure on that pipe is reduced, the automatic brake valves on each car respond by applying the brakes. A substantial drop—such as 70 psi—triggers the brakes quickly and typically as an emergency-type signal, causing air from the car’s reservoirs to flow into the brake cylinders and apply the brakes across the entire train. Since the brake pipe runs through every car, the braking action is transmitted along the train, leading to an immediate brake application everywhere, not just at the front locomotive.

In a train’s air brake system, brake pipe pressure acts as the control signal for braking. When the pressure on that pipe is reduced, the automatic brake valves on each car respond by applying the brakes. A substantial drop—such as 70 psi—triggers the brakes quickly and typically as an emergency-type signal, causing air from the car’s reservoirs to flow into the brake cylinders and apply the brakes across the entire train. Since the brake pipe runs through every car, the braking action is transmitted along the train, leading to an immediate brake application everywhere, not just at the front locomotive.