Class William Mason (Locobase 5585)

Data from reproduction of 1950 reprint of 1883 Recent Locomotives as hosted by http://www.ironhorse129.com/Prototype/MasonBogie/wmMason_0-6-6.htm (visited 2 June 2003). See also "Some Old Mason Engines," Railroad & Locomotive Engineering , December 1900, p. 535. The boiler pressure is an estimate. Mason's works number was 536.

Ironhorse129's commentary notes that this was the first locomotive in the United States using Egide Walschaert's radial valve gear. Australian ferroequinologist and live-steam enthusiast David Fletcher says that the Stephenson gear normally used wouldn't work for an engine whose drivers pivoted on a bogie as this Mason Bogie did. The distance between the lifting rod, which controls cutoff, and the engineer's actuating Johnson bar would vary and the engine would speed up or slow down as a consequence. The Walschaert layout allowed for placing the lifting rod up in front of the steam dome in an arrangement that fixed the distance.

The writer of the RLE article praised the William Mason's pulling power, saying: "There is possibly no engine today, of her dimensions, that could, under the conditions of the day and time, equal this engine for the amount of work done. Had she not had a bogie of old design, the late J N Lauder would have repaired her .... The engine could haul 125 long freight box cars, such as were used at the time between Mansfield and Fitchburg, and the grades were heavy, so Mr Hobart Piper, her engineer, informs us. "

Another 0-6-6T, Canada Atlantic 724, was the first and only Mason Bogie to run on Canadian rails and the first Canadian engine to use Walschaert's gear. See http://www.proto87.org/ca/loco/724.html . NB: For an explanation of the use of the singular "Walschaert", see Locobase 11157.