Pennsylvania Railroad class M1

Pennsylvania Railroad M1
PRR M1a on display at the 1939 World's Fair. Pipe on the smokebox and box behind stack are components of the feedwater heater.
Type and origin Power type Steam Builder PRR Altoona Works, Baldwin Locomotive Works, Lima Locomotive Works Serial number Lima 7099–7123, 7443–7467 Build date 1923-1930 Total produced 301
Specifications Configuration: ​  • Whyte 4-8-2 Gauge 4 ft 8+1⁄2 in (1,435 mm) Driver dia. 72 in (1.829 m) Wheelbase: ​  • incl. tender 79.32 ft (24.18 m) Length Loco: 54 ft 11 in (16.74 m) Tender: 52 ft 11 in (16.13 m) Width 10 ft 0 in (3.05 m) Height 15 ft 6 in (4.72 m) Axle load 67,750 lb (30,700 kg; 30.7 t) Adhesive weight 271,000 lb (123,000 kg; 123 t) Loco weight 390,000 lb (177,000 kg; 177 t) Tender weight 378,360 lb (172,000 kg; 172 t) Total weight 768,360 lb (349,000 kg; 349 t) Water cap. 22,090 US gal (83,600 L; 18,390 imp gal) Tender cap. 31.5 short tons (28.6 t; 28.1 long tons) Firebox: ​  • Grate area 69.90 sq ft (6.494 m2) Boiler 84+1⁄2 in (2,146 mm) Boiler pressure M1a: 250 psi (1.72 MPa), M1b: 270 psi (1.86 MPa) Cylinders Two Cylinder size 27 in × 30 in (686 mm × 762 mm) Valve gear Walschaerts Valve type Piston
Performance figures Maximum speed 70 mph (110 km/h) Power output M1a: 4,034 hp (3,008 kW) Tractive effort M1a: 64,550 lbf (287.1 kN), M1b: 69,700 lbf (310.0 kN) Factor of adh. M1a: 4.20, M1b: 3.89
Career Operators Pennsylvania Railroad Class M1, M1a, Number in class M1: 201, M1a: 100 Numbers M1: 6699, 6800–6999, M1a: 6700–6799 Retired 1957 Preserved 1 Disposition #6755 preserved, one tender preserved and set to be used on T1 new build, remainder scrapped
[1]

The M1 was a class of steam locomotive of the Pennsylvania Railroad (PRR). It was a class of heavy mixed-traffic locomotives of the 4-8-2 "Mountain" arrangement, which uses four pairs of driving wheels with a four-wheel guiding truck in front for stability at speed and a two-wheel trailing truck to support the large firebox needed for sustained power. Although built for both passenger and freight work, they spent most of their service lives hauling heavy high-speed freight trains. Many PRR men counted the M1 class locomotives as the best steam locomotives the railroad ever owned.^{[citation needed]}