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the Fisheries Research Board of Cana- da showed that the use of the over- head-bunker car solved this problem as spatial temperature variations were reduced to only two or three degrees. A similar result might have been achieved by using circulating fans in end-bunker cars, as in the United States, but this solution was not ac- ceptable to Canadian railways because of mechanical difficulties experienced under winter operating conditions. It was well known that the ordinary end-bunker refrigerator car could not be loaded to full cubic capacity and at the same time afford efficient refriger- ation. With the ice located at both ends of the cars, air circulation was slow and wide differences in temperature existed between the top, or the warmest part of the load, and the bot- tom, or coldest part of the load. These differences could range from 10 to 20 degrees. No single factor was responsible for


the development of the overhead- bunker car. It was believed that the overhead-bunker car provided a satis- factory general-purpose solution to Canadian refrigerator car operating conditions and requirements. Canadi-


an National and Canadian Pacific me- chanical engineers committed to the overhead-bunker design for general use for several reasons: 1. larger vol- ume capacity was available with 300 additional cubic feet; 2. larger loading capacity, 75,000 pounds versus about 35,000 pounds in end-bunker cars; 3. less internal temperature variation could be maintained with more uni- form temperature; 4. lower cost of re- frigeration during transit, less re-icing saving time and ice; 5. a permanent heater could provide year-round suit- ability; 6. no requirement would be needed to build and maintain single- purpose car fleets for specific commodi- ties; 7. unreliability of axle-driven cir- culating fans in Canadian winter conditions. The overhead-bunker cars had eight


9-inch deep containers in the roof for crushed ice and salt with eight roof hatch openings, four on each side of the running board. Hatches were closed when the car was refrigerating or heat- ing; otherwise they could be in the open position for ventilation. The melt from the ice containers was caught in drip pans located beneath the ice con- tainers and was carried down through


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