Pennsylvania Railroad K4 class

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Pennsylvania Railroad K4 class
PRR No. 3863 being inspected and maintained in the late 1920s
Type and origin Power type Steam Designer J.T. Wallis, Alfred W. Gibbs, and Axel Vogt Builder PRR's Juniata Shops (350), Baldwin Locomotive Works (75) Build date 1914-1928 Total produced 425
Specifications Configuration: ​  • Whyte 4-6-2 Gauge 4 ft 8+1⁄2 in (1,435 mm) Leading dia. 36 in (914 mm) Driver dia. 80 in (2,032 mm) Trailing dia. 50 in (1,270 mm) Length 83 ft 6 in (25.45 m) Height 15 ft 0 in (4.57 m) Axle load 66,500 lb (30,200 kg; 30.2 t) Adhesive weight 199,500 lb (90,500 kg; 90.5 t) Loco weight 304,500 lb (138,100 kg; 138.1 t) Tender weight 212,725 lb (96,490 kg; 96.490 t) Total weight 517,225 lb (234,609 kg; 234.609 t) Fuel type Coal Fuel capacity 32,000 lb (15,000 kg; 15 t) Water cap. 7,000 US gal (26,000 L; 5,800 imp gal) Firebox: ​  • Grate area 69.89 sq ft (6.493 m2) Boiler 78+1⁄2 in (1,994 mm) Boiler pressure 205 psi (1.41 MPa) Cylinders 2 Cylinder size 27 in × 28 in (686 mm × 711 mm) Valve gear Walschaerts Valve type Piston valves
Performance figures Maximum speed 87 mph (140 km/h) Power output 3,286 hp (2,450 kW) Tractive effort 44,460 lbf (197.8 kN) Factor of adh. 4.54
Career Retired 1938 (1), 1947 (2), 1949-1958 Preserved Nos. 1361 and 3750 Disposition Two preserved, remainder scrapped

The Pennsylvania Railroad K4 was a class of 425 4-6-2 steam locomotives built between 1914 and 1928 for the PRR, where they served as the primary main line passenger steam locomotives on the entire PRR system until late 1957.

Attempts were made to replace the K4s, including the K5 and the T1 duplex locomotive. However, the low factor-of-adhesion of K5s meant that they were limited in their pulling power. By contrast, the T1s were very successful but suffered from greater maintenance costs, wheel slip due to poor springing, and inexperienced crews. The T1s also came too late in the game for steam traction. As such, the tried and tested K4s held their role as the PRR's primary express passenger locomotives for 30-40 years. The K4s hauled the vast majority of express passenger trains until they were replaced by diesel locomotives.

The K4s were not powerful enough for the heavier trains they often pulled from the mid-1930s onward, so they were often double-headed or even triple-headed, sometimes with early Atlantics and E6s. This was effective but expensive, and several crews were needed. The PRR did have the locomotives needed for this, many having been displaced by electrification east of Harrisburg.

The two preserved K4s, Nos. 1361 and 3750, were designated as Pennsylvania's official state steam locomotives on December 18, 1987, when Pennsylvania Governor Robert P. Casey signed into law House Bill No. 1211.