Pennsylvania Railroad class Q2

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The Pennsylvania Railroad's class Q2 comprised one prototype and twenty-five production duplex steam locomotives of 4-4-6-4 wheel arrangement.[1][2][3]

Pennsylvania Railroad class Q2
PRR Q2.jpg
PRR Q2 prototype #6131[1]
Front angle view of a Q2.
Front angle view of a Q2.
Type and origin
Power typeSteam
BuilderPRR Altoona shops
Build date1944–45[1]
Total produced26[1]
 • Whyte4-4-6-4[1]
 • UIC2'BC2'
Gauge4 ft 8 12 in (1,435 mm) standard gauge[1]
Leading dia.36 in (0.914 m)[1]
Driver dia.69 in (1.753 m)[1]
Wheelbase26 ft 4.5 in (8.039 m) (driving)
20 ft 4 in (6.20 m) (rigid)
53 ft 5.5 in (16.294 m) (locomotive)
107 ft 7.5 in (32.804 m) (locomotive and tender)[1]
Length124 ft 7.125 in (37.976 m) (locomotive and tender)[1]
Width11 ft 4 in (3.45 m) (storm windows open)[1]
Height16 ft 5.5 in (5.017 m)[1]
Adhesive weight393,000 lb (178,000 kg; 178 t)[1]
Loco weight619,100 lb (280,800 kg; 280.8 t)[1]
Tender weight430,000 lb (195,000 kg; 195 t)[1]
Total weight1,049,100 lb (475,900 kg; 475.9 t)[1]
Tender typePRR class 180F84, 8 axles, with conductor "doghouse"
Fuel typeSoft coal
Fuel capacity39.86 short tons (36.16 t; 35.59 long tons)[1]
Water cap19,020 US gal (72,000 l; 15,840 imp gal)[1]
Boiler pressure300 psi (2.1 MPa)
Front cylinder19 34 in × 28 in (502 mm × 711 mm)
Rear cylinder23 34 in × 29 in (603 mm × 737 mm)
Performance figures
Power output7,987 hp (5,956 kW)[1]
Tractive effort100,816 lbf (without booster) / 115,816 lbf (with booster)
OperatorsPennsylvania Railroad[1]
Numbers6131, 6175–6199[1]
Last run1951

They were the largest non-articulated locomotives ever built and the most powerful locomotives ever static tested, producing 7,987 cylinder horsepower (5,956 kW) on the PRR's static test plant. They were by far the most successful duplex type. The duplex propensity to slip was combated by an automatic slip control mechanism that reduced power to the slipping unit.

The Q2 locomotive was 78% more powerful than the locomotives that PRR had in service at the time, and the company claimed the Q2 could pull 125 freight cars at a speed of 50 mph (80 km/h). [4] These were an improved version of the previous Q1 class, which was a 4-6-4-4 dual-purpose engine instead of a 4-4-6-4 freight engine.

Despite the overall success, the Q2s were all out of service by 1951. With dieselization, they were the obvious first targets to be withdrawn since they were only a little more capable than the conventional J1 class 2-10-4s but with far higher operating and maintenance costs. The final Q2, 6199's power output is 7,987 hp. All have been scrapped and none were preserved.


  1. ^ a b c d e f g h i j k l m n o p q r s t u Harley, E.T. (1982). Classic Power 5: Pennsy Q Class. Hicksville, New York: N.J. International. ISBN 0-934088-09-8.
  2. ^ Staufer, Alvin (1962). Pennsy Power. Staufer. pp. 216–225. LOC 62-20872.
  3. ^ Brian Reed (June 1972). Loco Profile 24: Pennsylvania Duplexii. Windsor, Berkshire, UK: Profile Publications.
  4. ^ "4-Cylinder Engine Has 78% More Power." Popular Mechanics, December 1944, p. 13.