Each car on a freight train is equipped with what is called a brake control valve. This valve is in the automatic air brake system and causes the air brake on the individual car to be applied when the pressure in the main brake pipe which runs throughout the train is reduced by the engineer or by any other cause. Sometimes, the brake control valve will malfunction, thereby causing it to go into the emergency brake position, either during normal service braking or at other times. When it goes into the emergency position, the brake pipe opens to the atmosphere and the resulting sudden reduction in pressure at that point causes all of the brake control valves on the train to go into emergency position causing a full emergency brake application throughout the train. With long trains, quickly finding the malfunctioning brake control valve is quite a chore. This invention provides a method and means of almost immediately indicating the location of a defective brake control valve by timing a pressure wave front propagated by the malfunctioning valve to the front and rear ends of the train in response to separate transducers which transmit radio frequency(RF) signals to a receiver and separate counters which count clock pulses from the time of receipt of respective RF signals to determine difference in the time for the pressure wave to reach the ends of the train to determine the location of malfunction from one end or the center of the train, depending upon the clock pulse rate used.
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