What does an engineer do to the brake pipe pressure to apply the train brakes?

What does an engineer do to the brake pipe pressure to apply the train brakes?

• A. Lowers the brake pipe pressure
• B. Raises the brake pipe pressure
• C. Maintains the brake pipe pressure
• D. Fluctuates

Answer: (A)

In an air-brake system, braking is triggered by lowering the brake pipe pressure. When the engineer reduces the pressure in the brake pipe, the brake-control valves detect this drop and cause air from the reservoir to flow into the brake cylinders, moving the pistons and applying the brakes. Restoring the brake pipe pressure releases the brakes, and keeping it the same or letting it fluctuate won’t produce a controlled braking action. This design is also fail-safe: any loss of brake pipe pressure along the train will apply the brakes automatically.

In an air-brake system, braking is triggered by lowering the brake pipe pressure. When the engineer reduces the pressure in the brake pipe, the brake-control valves detect this drop and cause air from the reservoir to flow into the brake cylinders, moving the pistons and applying the brakes. Restoring the brake pipe pressure releases the brakes, and keeping it the same or letting it fluctuate won’t produce a controlled braking action. This design is also fail-safe: any loss of brake pipe pressure along the train will apply the brakes automatically.