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Old 02-05-2017, 06:27 PM
Toledo Jim Toledo Jim is offline
Join Date: Nov 2013
Location: Toledo
Posts: 120
The rule I heard is that he driver diameter in inches equals the running speed in miles per hour, which is close to what Snnipe 70E said. The top speed would be a bit higher, limited by the effective piston speed. You just can't get steam into and expanding and out of the cylinder fast enough beyond a certain point.
Some designs were limited in sustained speed by the boiler capacity, there was only so much steam available. Running beyond that point started to pull down the boiler pressure, essentially strangling the locomotive. Erie RR had two giant locomotives with three sets of driving wheels. Which meant three pairs of cylinders, etc, the third set of drivers was under the tender. The boiler couldn't mke enough steam to supply all that except at a very low speed and load. The Virginian RR had similar triplex locomotives, all of them (both rrs) had a short operating life.