Walschaerts gear. I don't recall the dates, but I believe Loco's built
into the 1910-1920's were still being built with Stephenson gear. I
I believe CP’s last engines delivered with Stephenson gear was 1913 or there
about. But you’re right that some railways kept delivering engines with
Stephenson gear for much longer.
Stephenson gear grew out of favour because as axle diameters increased so did
the size and weight of the eccentrics and the rest of the gear. Larger and
more powerful engines had heavier frames and more bracing between the side
frames so there was less space to fit inside frame gear.
could be innovative. The CPR was one of the first to try things like
superheating and nickel boilers so they must have had a good reason to
keep using the Stephenson valve gear.
Early engines that were rebuilt in the 1910’s i.e,, 4-4-0, 4-6-0 and 2-8-0’s.,
were given a higher pressure boiler with super heater and piston valves (slide
valves don’t work with high pressure). With that being done you’ve increased
the efficiency of the engine by a fairly large amount. How much more do you
get by replacing the valve gear? It might not have been enough to justify the
work.
Jeff Pinchbeck
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