In engines such as a mallet, with four sets of cylinders, does the engineer have a separate throttle for each set of cylinders and two Johnson bars?
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Tommy posted:In engines such as a mallet, with four sets of cylinders, does the engineer have a separate throttle for each set of cylinders and two Johnson bars?
No. Only one throttle, and only one reverse gear.
Thanx...
Some rack locomotives have separate sets of cylinders for the rack drive and for the drive wheels, with separate throttle control for each set, because the rack operation is used only on the steepest sections, not continuous. Can't think of any American examples like that but various other countries have them.
Tasmania Wilderness Railway operational 0-4-2T rack locomotives built 1898. Photos by Ace 2009.
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Tommy posted:In engines such as a mallet, with four sets of cylinders, does the engineer have a separate throttle for each set of cylinders and two Johnson bars?
Some French compound locomotives did have separate controls to achieve better efficiency and performance.
http://mikes.railhistory.railfan.net/r102.html
Two eminent locomotive engineers were concerned—A.G.deGlehn and his successor. G. du Bousquet —who established the compound locomotive practice that is jointly associated with their names, and laid a foundation on which practically every French railway has since built.
... An essential feature of the de Glehn-du Bousquet compound arrangement is four independent sets of Walschaerts valve-motion, and independent cut-off adjustment for both sets of cylinders, so that the driver has two reversing gears to control as well as the opening of his regulator. In other ways the average French footplate, with its mass of controls, looks a considerably more complex affair than the average footplate in Great Britain. But the French driver appears to thrive on complications, and it is largely to his traditional driving skill that the success of locomotive compounding in France has been due.
Records show that as far back as 1900 the Nord compounds were already putting up remarkable performances. In that year a 4-4-0 compound ran the 95.1 miles from Paris to St. Ouentin, with the "Nord Express," in 85-1/4 minutes ; the best schedule to-day is 88 minutes. Loads, of course, were light in those days, and the weight of the train amounted to only 113 tons. Up the 1 in 200 to Survillicrs speed was maintained at 67, and the train travelled on the level at 76 miles an hour.
an example of an American rack loco would be the Mt. Washington cog railway. though it is 100% rack driven. no sections without a rack.
In addition to what ACE said, I believe the french 2-3-1 , (4-6-2 in American convention ), redesigned by Chapelon also retained the ability to start the low pressure cylinders with a blast of hp steam just to help get things moving. MTH made some really nice 1:45 scale models of them.
I believe it was not unusual for compound articulated locomotives to have a "starting valve" so the locomotive could operate "simple" for starting a train. This fed steam direct to all cylinders, but with the larger low-pressure cylinders receiving steam through a reducing valve so both sets of drivers would generate approximately equal power. When the train got moving it switched to compound operation for more economical use of steam. Not sure if the starting valve was cut out automatically or manually - maybe automatic on some.
N&W Y5-Y6 class 2-8-8-2 were the last and biggest of successful American compound articulated steam locomotives, surviving right up to the end of mainline steam circa 1959.
