We have performed experimental studies for the improvements of pneumatic brake systems of freight trains. Currently, most of the freight trains operated by the Korean National Railroad have either empty-load or diaphragm type brake systems. In this study, the differences in the air pressure characteristics of both types of brake systems are investigated. Also, we have performed running tests using a 30 car - train set in order to design optimum capacity of a quick release valve. The test results show that the quick release valve is considerably effective in shortening the release time of the diaphragm type brake system. In the case of a normal brake application, the diaphragm type brake system with the quick release valve reduces the release time to 34% of that of the system without the quick release valve. This release time is almost equivalent to that of the empty-load type brake system. Proper performance of a brake system in a train set, preventing wheel flats and reducing maintenance costs, is very crucial.
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