Union Railroad 0-10-2 "Union" Locomotives in the USA

Class U-108b/S7 (Locobase 5976)

Data from Ransome-Wallis (1959) and "The First 'Union' Type Locomotive," Baldwin Locomotive Magazine, Volume 15, No 1 (July 1936), pp. 1-6, See also [] (4 April 2004) and the DM&IR photo site [] (4 April 2004_) and the DM&IR 1960 Locomotive Diagrams book supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. Works numbers 61907-61911 in June 1936 and 62059-62062 in 1937.(Thanks to Chris Hohl for noting the tender booster.)

Locobase doesn't usually include US yard switchers, but makes an exception for this Union class for two reasons: 1) sheer brute size, and 2) its use in transfer service. Well, really it's the size. This was an enormous design, quite suitable for the US Steel railroad on which it operated.

Its unusual arrangement stemmed from the short Union turntables, need for high adhesive weight and power, and relatively short runs. The large firebox -- fitted with three thermic syphons (90 sq ft/8.35 sq m) and a combustion chamber (72 sq ft/6.7 sq m) -- needed a trailing axle and the short turntables and low operating speeds permitted dispensing with a lead truck. Even with the low speeds and relatively tall drivers, each driver set needed substantial counterbalancing. Cast-steel bar frames were bolted to rear cast-steel cradles that also made up the cab's footplate. Equalization followed a typical pattern in which the front three driven axles were equalized as a unit and the last two driving axles and the rear truck were equalized together.

About the only undersized parts were the two 12" (305 mm) piston valves, which had a travel of 7 3/4" (197 mm). A continuous run of boiler cladding from the firebox to the front edge of the smokebox produced an unusually smooth line.

The Greenville site says the tender's capacity was about right for a full day's work. To start especially heavy loads, these engines were fitted with powerful tender boosters. These were Franklin Reversible Boosters that operated at 50% cut-off and still delivered 17,150 lb of tractive effort.

After World War II, the Union bought diesels and sold the Unions to the Duluth, Missabe and Iron Range. "Hot Metal" wrote to the Railway Preservation News forum on 14 March 2013 to report that the booster was removed when they were sold. The DM&IR compensated for the removed booster by adding weight to the locomotive frame. The 1951 DM&IR diagram shows adhesion weight as 364,600 lb (165,380 kg) and engine weight of 422,000 lb (191,416 kg).

Most of these operated well into the 1950s. 607, shown on the DM&IR site, was scrapped in 1958, but 604 was returned to the URR for display in 1961.