Improving brake propagation in long freight trains

Brake propagation is slow for long freight trains that use a conventional air brake system. If the train is too long then the brake application will not propagate throughout the whole train. Brake propagation is one of the factors that limit the length of current heavy haul freight trains using a conventional air brake system. It is possible that a relatively simple modification to every wagon's brake valve could be done to ensure the brake signal is relayed throughout the train irrespective of the length of the train.The modification effectively increases the quick service volume or 'bulb' on Westinghouse style triple valves by connecting an additional volume and valve to the brake pipe. As each wagon's brakes apply, extra air will be taken from the brake pipe to fill the additional volume and thus ensuring the propagation of the brake signal to the rear of the train. The modification also has the advantage of reducing the time for the brakes to reach their final pressure, which reduces the train's stopping distance.A computer model of a complete train air brake system developed through the Rail CRC is used to discuss the advantages and disadvantages of the modification. Using air brake equipment at CQU, experimental tests have been conducted to determine the allowable size of the additional volume and show the stability of the modification.