The Robinson Class S1 0-8-4 Tank Locomotives

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Robinson designed these powerful 0-8-4 tank locomotives in 1907 for hump shunting the newly opened Wath-on-Dearne marshalling yard in South Yorkshire. Initially, four were built between 1907 and 1908. Robinson based the S1 on his 8-coupled tender engines (LNER Q4), but had three cylinders for smooth powerful uphill shunting. Due to the extra cylinder, a slightly wider boiler was fitted. Power reversing gear was also fitted due to the constant reversing experienced in a busy marshalling yard.  These engines were generally successful, although sometimes two were needed together to shunt the heaviest trains in wet weather. Hence in 1930, Gresley tried fitting a booster to the trailing bogie. Boosters apply extra power at very slow speeds, and are usually used for starting heavy loads. Due to these being shunters, the S1 boosters were unusual because they were reversible (ie. applied power in both directions). Due to the required replacement of the complete bogie, it was considered economical to build new engines for the boosters. Hence, one locomotive (No. 6171) had a booster fitted, and two new locomotives were built with boosters in 1932. The unmodified engines were designated S1/1, whilst No. 6171 (modified) became S1/2, and the two new engines became S1/3.
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The Robinson Class S1 0-8-4 Tank Locomotives - Railway-Photography
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