Train brakes, particularly the common air brake systems, operate on a fundamental principle involving changes in air pressure within the brake pipe that runs throughout the train.
The Principle of Train Air Brakes
The core mechanism of how train air brakes function relies entirely on precise control of air pressure. As outlined by the Transportation Safety Board of Canada (TSB), "The principle of train air brakes is based on lowering brake pipe pressure to apply the brakes and increasing brake pipe pressure to release the brakes."
For this intricate system to operate effectively and as designed, it has a crucial prerequisite: "The train air brake system must be sufficiently charged with compressed air."
How Air Pressure Controls Braking
The continuous brake pipe runs from the locomotive through every car, acting as the central control line for the entire braking system. Changes in the pressure within this pipe dictate whether the brakes are applied or released:
- Brake Application: When the locomotive engineer initiates braking, the system actively lowers the brake pipe pressure. This reduction in pressure signals each car's braking mechanism (which includes auxiliary reservoirs and control valves) to apply the brake shoes against the train wheels. The resulting friction slows or stops the train.
- Brake Release: To disengage the brakes and allow the train to move freely, the system increases the brake pipe pressure. This rise in pressure signals the control valves on each car to release the brake shoes from the wheels.
The Essential Role of Compressed Air
Compressed air is the power source for the entire air brake system. It is supplied from compressors on the locomotive and stored in reservoirs throughout the train. This continuous supply of compressed air is vital for:
- Charging the system: Ensuring the brake pipe and individual car reservoirs have sufficient pressure.
- Rapid response: Allowing quick and reliable application or release of brakes across all cars simultaneously.
Without adequate compressed air, the system cannot generate the necessary pressure differences to operate, rendering the brakes ineffective.
