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Pennsylvania Railroad class Q2
PRR Q2.jpg
PRR Q2 prototype #6131[1]
Type and origin
Power type Steam
Builder PRR Altoona shops
Build date 1944–45[1]
Total produced 26[1]
Configuration 4-4-6-4[1]
UIC classification 2'BC2'
Gauge 4 ft 8 12 in (1,435 mm)[1]
Leading wheel
36 in (0.91 m)[1]
Driver diameter 69 in (1.75 m)[1]
Wheelbase 26 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]
Length 124 ft 7.125 in (37.976 m) (locomotive and tender)[1]
Width 11 ft 4 in (3.45 m) (storm windows open)[1]
Height 16 ft 5.5 in (5.017 m)[1]
Weight on drivers 393,000 lb (178,000 kg)[1]
Locomotive weight 619,100 lb (280,800 kg)[1]
Tender weight 430,000 lb (195,000 kg)[1]
Locomotive and tender
combined weight
1,049,100 lb (475,900 kg)[1]
Tender type PRR class 180F84, 8 axles, with conductor "doghouse"
Fuel type Soft coal
Fuel capacity 39.86 short tons (36.16 t)[1]
Water capacity 19,020 US gal (72,000 l; 15,840 imp gal)[1]
Boiler pressure 300 psi (2.1 MPa)
Front cylinder
19 34 in × 28 in (500 mm × 710 mm)
Rear cylinder
23 34 in × 29 in (600 mm × 740 mm)
Performance figures
Power output 7,987 hp (5,956 kW)[1]
Operator(s) Pennsylvania Railroad[1]
Number(s) 6131, 6175–6199[1]
Last run 1951
Front angle view of a Q2.

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]

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. [4]

Despite 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 With dieselization, they were the obvious first targets to be withdrawn since they were only a little more capable than the conventional J1 class 2-10-4s but with far higher operating and maintenance costs.


  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.