1. The Architecture of the Automatic Air Brake
UIC 543 specifies the regulations governing the equipment of trailing stock (coaches and wagons). It defines the fundamental logic of the “Automatic Compressed Air Brake”:
Safety by Physics. If the brake pipe (BP) is ruptured (train separation), the pressure drops, and the brakes automatically apply on every vehicle.
This standard dictates the performance of the Distributor Valve, which translates the pressure drop in the Brake Pipe (typically 5.0 bar to 3.5 bar) into brake cylinder pressure.
2. Braking Modes: The “G-P-R” System
The most searched technical aspect of UIC 543 is the definition of Braking Modes. These modes determine how fast the brake applies and releases, managing the longitudinal forces in the train.
| Mode | Full Name | Filling Time (Application) | Releasing Time | Typical Application |
|---|---|---|---|---|
| G | Goods (Freight) | Slow (18 – 30 sec) | Slow (45 – 60 sec) | Long freight trains (>700m). Slow action prevents “Train Bunching” and coupler breakage. |
| P | Passenger | Fast (3 – 5 sec) | Fast (15 – 20 sec) | Passenger trains and short freight trains (up to 100km/h or 120km/h). |
| R | Rapid (High Power) | Fast (3 – 5 sec) | Fast (15 – 20 sec) | High-speed trains (>140km/h). Features High Power braking (often >130% brake weight). |
3. Braked Weight & Braking Percentage (Lambda)
UIC 543 defines the calculation of “Braked Weight”. This is not the physical mass of the equipment, but a performance value derived from stopping distances.
- Calculation: (Braked Weight / Total Train Mass) x 100 = Braking Percentage (%).
- Significance: A train cannot depart unless its calculation meets the minimum braking percentage required by the line signaling (e.g., a line requiring 115% means only high-performance R-mode vehicles can operate effectively).
4. Mechanical Adjustments: The Slack Adjuster (DRV)
As brake blocks or pads wear down, the gap between the friction material and the wheel increases.
- Requirement: UIC 543 mandates the installation of an automatic Slack Adjuster (Regulator).
- Function: It mechanically shortens the rigging linkage to maintain a constant piston stroke (and constant braking force) regardless of whether the blocks are new (40mm) or worn (10mm).
Design Note: For wagons with varying loads (Empty vs. Loaded), UIC 543 requires a “Load-Proportional” system (Auto-continuous weighing valve) to increase brake cylinder pressure as the wagon gets heavier, preventing wheel flats when empty and ensuring stopping power when full.
