Class KK-1 (Locobase 3099)

Data from B&O to 1954 Assorted Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange collection. See also "Test Locomotives of 4-8-2 and 2-6-6-2 Types on the B&O", Railway Age, Volume 91, No 2 (11 July 1931), pp. 46-49; and United States Patent 1,909,874, awarded 16 May 1933. (Thanks to Chris Hohl for his 28 October 2019 email noting the driving wheelbase.) Works number was 61571 in November 1930.

Like the T-1/T-2 4-8-2 comparison, the KKs were built in single copies to compare the Emerson watertube firebox to a conventional locomotive. This was the EWT entry; its conventional stalking (iron) horse appears in Locobase 296.

These are the only 2-6-6-2 articulateds the B&O operated other than the BR&P KK-1s (Locobase 295) and are almost unknown today. In the Emerson variant, a 40" (1016 mm) diameter drum ran along the centerline over the grate and from front sheet to back head. Headers at the top and bottom of the firebox were connected by two rows (190 tubes total) of 2 1/2"/63.5 mm diameter water tubes. The top header was joined to the drum by 13 4" (102 mm) diameter nipples on each side. In addition to the conventional fire tubes that extended from the front of the firebox to the smokebox, the Emerson firebox's sides consisted of 190 2 1/4" (57 mm) tubes, each 7 ft 10 in (2.39 m) long, that circulated water from bottom to top. Total heating surface area was calculated as 606 sq ft (56.30 sq m).

Each of the four large cylinders was served by a 12" (305 mm) piston valve.

This engine was converted briefly to a 4-4-6-2 arrangement for passenger service, but soon was restored as a Prairie Mallet and lasted until 1953.

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Class KK-2 (Locobase 296)

Data from B&O to 1954 Assorted Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange collection. See also "Test Locomotives of 4-8-2 and 2-6-6-2 Types on the B&O", Railway Age, Volume 91, No 2 (11 July 1931), pp. 46-49. (Thanks to Chris Hohl for his 28 October 2019 email correcting the engine wheelbase.) Works number was 61560 in November 1930.

The 7450 with the conventional stayed firebox was built to compare to the 7400 (Locobase 3099) with an Emerson watertube firebox. In addition to 110 sq ft (10.2 sq m) of heating surface in the combustion chamber, this engine's firebox heating surface at first included 46 sq ft (4.25 sq m) of arch tubes, but the appliance contribution was later revamped with 18 sq ft (1.65 sq m) of arch tubes and 95 sq ft (8.8 sq m) of thermic syphons for a total of 403 sq ft (37.45 sq m).

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Class LL / KK-4 (Locobase 295)

Alvin F Staufer & Lawrence W Sagle, B & O Power (1964). Data confirmed by table in May 1916 RME and BR&P 11 - 1930 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. (Thanks to Chris Hohl for pointing out the valve gear IDs on the subclasses.)

These 55 locomotives were built at Alco's Schenectady and Brooks works from 1914 to 1923. All were delivered with 14" (356 mm) piston valves serving the HP cylinders and slide valves supplying the LP cylinders. All but the 7526-7540 batch from Brooks used Walschaert's valve gear. That set of fifteen was equipped with Southern gear.

Several batches delivered as follows, as classified by the B&O and renumbered in 1932:

Works numbers

KK-4 7500-7504 Schenectady 1914 54702-54706

KK-4a 7505-7509 Brooks 1917 57209-57213

KK-4b 7510-7525 Brooks 1918 57996-58011

KK-4c 7526-7540 Brooks 1918 58479-58493

KK-4d 7541-7554 Brooks 1923 64603-64616

One was rebuilt as KK-5 in 1949 with chassis lubrication, bed casting

Retired by 1951.