4-10-2

Under the Whyte notation for the classification of steam locomotives, a 4-10-2 locomotive has four leading wheels, ten driving wheels and two trailing wheels. It is generally termed the "Southern Pacific" type. The class ran and rode better than the 2-10-2 type of locomotives.Swengel, p. 222.]

Other equivalent classifications are:

UIC classification: 2'E1' (also known as German classification and Italian classification)

French classification: 251

Turkish classification: 58

Swiss classification: 5/8

United States

According to Boynton's, definitive book on the 4-10-2 in the U.S.A., there were only sixty engines built for domestic service and all were constructed as three cylinder engines. So it is impossible to discuss that wheel arrangement, without also discussing three cylinder development.

In 1925 the Southern Pacific (SP) placed an order for 16 locomotives, while in the same year, the Union Pacific (UP) placed a pilot order for one engine, No. 8000. Boynton said, the design was revolutionary and the SP engine No. 5000 completed in April 1925 bore builder's plate number 66107 while the UP engine completed in May 1925, carried builder's plate number 66169.Boynton, p.2.]

Within a few months, the SP re-ordered more engines and built up a fleet of 49 locomotives, but the UP waited thirteen months before repeating orders and establishing a fleet of 10 machines. Total orders thus far, 59 engines.

The SP engines had three cylinders; inside cylinder 25 x 28 inches; the two outside cylinders 25 x 32 inches; boiler pressure convert|225|psi, grate area convert|89.6|sqft|m2 and tractive effort convert|84200|lbf|kN|abbr=on. The boosters, utilised for a while, generated a further convert|12340|lbf|kN|abbr=on and when fitted gave those locomotives a T.E. of convert|96540|lbf|kN|abbr=on.Boynton, p. 114.]

The UP engines (1925-42) had three cylinders; the inside was 25" x 28"; the two outside cylinders 25" x 30"; boiler pressure convert|210|psi|abbr=on; fire grate convert|84|sqft|m2 and a tractive effort of convert|72000|lbf|kN|abbr=on.Boynton, p. 134.]

Then in 1926, Baldwin Locomotive Works constructed an experimental demonstrator, No. 60000, which was different from those 59 simple expansion locomotives, which preceded it. Number 60000 was a compound and the only 4-10-2 so constructed. This engine used high pressure steam in the inside cylinder, then exhausted that steam into the two outside cylinders. The boiler operated at convert|350|psi|abbr=on and delivered convert|82500|lbf|kN|abbr=on of tractive effort. The grate area was convert|82.5|sqft|m2. Baldwin's 4-10-2 was, said Boynton, 'outmoded before she left the factory' as steam compounding had lost favour in US railroading.Boynton, p.5 & 144-149.]

The three cylinder feature on these locomotives gave them a distinctive sound at work, described in Boynton, as a 'hop, skip, jump rhythm'. The third cylinder, located in the centre of the cylinder saddle, sloped down at an 11 degree angle connecting to the second driver's axle, while the two outside rods connected onto the third driver. The inside third rod, which connected onto the second driver created 'endless maintenance problems' because the floating bushings failed. Adding to the railway's maintenance problem the failures required major valve settings and delays. Another unusual problem with the SP engines, Boynton said, was that the mechanical failures created such great pounding on the rails that railway housewives along the line complained of crockery cracking when a defective 4-10-2 rumbled past their homes.Boynton, p. 6.]

The Union Pacific, said Boynton, tired of the heavy mechanical problems associatied with three cylinders and in 1942, converted its engines to two-cylinder locomotives and renumbered them 5090-5099; and this action reduced the 60 locomotives of the three cylinder 4-10-2 fleet to 50 engines. Following the conversion to two cylinders the UP engines had the following: two outside cylinders 27 x 32 inches and tractive effort convert|72400|lbf|kN|abbr=on.

The SP engines, said Swengel, could only operate on main lines and because of their size could not be relegated to secondary or branch lines. Their long lives (from 28 to 30 years of service on the main line) was proof that they were good locomotives. However, despite the impressive service of the 4-10-2s on the UP, said Sengel, that railway still required bigger power that led to the building of the fleet of 4-12-2s.

In November 1946, one of SP 4-10-2 engines No.5037 suffered a boiler explosion which killed four train crew.Boynton, pp. 84-98.]

Preservation

Two locomotives of this type have been preserved, including:
* Southern Pacific 5021, static display at the Los Angeles County Fairgrounds, Pomona, California
* Baldwin 60000, moving display at the Franklin Institute Science Museum

References

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