New low loss valves have been designed for an existing railroad air brake compressor. Prototypes of these valves have been built and tested in the laboratory. These valves increase the efficiency of the compressor by 13% when operating at full load and rated speed with corresponding improvements at lower speed and when unloaded. Total operating hours on the test compressor with the high efficiency valves installed total over 4000 as of 1/1/86.The Association of American Railroads has a committee working to find ways of increasing locomotive and rolling stock efficiency and hence reducing fuel costs. As part of this task, the committee considered ways of reducing the power consumption of the air brake compressor. We at Worthington Dresser were asked whether the technology we had developed to increase the efficiency of large stationary compressors could be applied to the locomotive compressor. A theoretical study indicated that a significant improvement could be achieved and so the development of suitable valves was started using a compressor loaned to us by Conrail.