H-4-A, C&O's simple 2-6-6-2, The

The C&O. wasn't generally a railway that went in for one-- of-a-kind locomotives, so the existence of just one class H-4-A simple 2-6-6-2 tells us that it was probably an experimental, and that certainly is the case.

B&O introduced the compound articulated steam locomotive into American railroading in 1904. This type of locomotive was most often referred to as "Mallet" from its French inventor, Anatole Mallet. Mallets had two engines (cylinder set and driving wheels) under one long boiler, the first engine being arranged so that it would swivel around curves independent of the second engine and using steam in a "compound" mode. C&O acquired its first Mallet, the H-1 class, in the summer of 1910. It was of the 2-6-6-2 wheel arrangement, indicating that each of its two engines had six driving wheels, plus a two-wheel leading truck and a two-wheel trailing truck under the firebox. The 2-6-6-2 became the C&O's standard heavy haul locomotive in the 'teens and twenties, supplemented in 1923-24 by the massive H-7 2-8-8-2. But the IL:7 was different. It was not a true Mallet because it was not "compound."

A compound locomotive delivered steam at full boiler pressure to the rear set of cylinders, and when it had expanded to drive back the piston and move the driving wheels, this steam, now at a lower pressure, was exhausted not into the atmosphere, but into the much larger second set of cylinders, where it was used once more to turn the first set of drivers. In this way the same steam produced almost twice as much mechanical power. This had many advantages, but the disadvantage was that the lower pressure steam didn't have the strength that could be generated if both sets of cylinders were supplied with high-pressure steam directly from the boiler. But, the more high-pressure steam required, the bigger the boiler - a limiting factor.

Although there had been spotty development of simple articulated designs, C&O's H-7 class 2-8-8-2 simple articulateds really established the design as successful in a large number of standard locomotives. In 1927, with the success of these large and very powerful locomotives just being fully proven, C&O's mechanical department decided to convert a single H-4 class 2-6-6-2 from compound to simple to see if this would be an appropriate retrofit for its large fleet of 2-6-6-2 compounds. H-4 No. 1470 was chosen. It was an ALCO-- Richmond product of 1918. Its 22x32-inch rear cylinder set was changed to 20x32 inches, and the large low-pressure front cylinder set of 35x32 dimension was replaced by another 20x32 set. Additional piping was necessary for delivery of boiler-steam to the front cylinder (see accompanying photos and diagrams). The old slide-valve front cylinders were replaced by piston valves. An outward appearance that was also noticeable was the double exhaust stack, characteristic of simple articulateds, as opposed to the usual single exhaust stack for the compounds and non-articulated simple engines.

The H-4-A, as the 1470 was reclassified, also had a frontend throttle installed, but in other appearances looked hardly different from the regular H-4s. The H-4-A was rated at 81,250 pounds of tractive effort, whereas the compound H-4s were rated at 74,200 pounds. The compounds were rated at 93,600 pounds when operating simple, but they were capable of simple operation only for a very short time, usually when starting a train, because their boiler capacity was insufficient to supply enough steam. The H-4-A was also slightly heaver, and had more heating surface in its flues by about 273 square feet. Its rated boiler pressure was 210 pounds as opposed to the H-4's 200 pounds. All other dimensions remained the same.

Apparently the H-4-A did not meet expectations in operation or no real need was felt for it, because, by 1930, C&O had entered the Lima Super Power era with the massive T-l class 2-10-4s. The single H-4-A stayed on the roster until was scrapped in March 1947. Until recently we had no good photos of this hybrid locomotive, but we have recently discovered the photos that accompany this article. They were taken on March 24, 1928, soon after the locomotive's modification. The drawings are taken from the C&O 1944 locomotive diagram book (reprints are available from the C&OHS). Anyone having additional photos of the 1470 or more information is asked to write us at the Clifton Forge address, Attention: Archives.

Copyright Chesapeake and Ohio Historical Society, Inc. Apr 1999
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