The Pennsylvania Railroad's class Q2 comprised one prototype and twenty-five production duplex steam locomotives of 4-4-6-4 wheel arrangement.
Front angle view of a Q2.
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).  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 With dieselization, they were the obvious first targets to be withdrawn since they were only a little more capable than the conventional J1 class 2-10-4s but with far higher operating and maintenance costs. References
^ 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. ^ Staufer, Alvin (1962). Pennsy Power. Staufer. pp. 216–225. LOC 62-20872. ^ Brian Reed (June 1972). Loco Profile 24: Pennsylvania Duplexii. Windsor, Berkshire, UK: Profile Publications. ^ "4-Cylinder Engine Has 78% More Power." Popular Mechanics, December 1944, p. 13.
v t e
A1 A2 A3 A4 A5s
B1 (s) B2 B3 B4 B5 B6 B7 B8 B1 (e)
C1 C29 C30 C31
D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 D15 D16 D21 D22 D23 D24 D25 D26 D30 D31 D32 D33 D34 D35 D36 D37 D38 D39 D61 "Odd D" #10003
E1 E2 E3 E4 E5 E6 E7 E21 E22 E23 E28 de Glehn
F1 F2 F3 F21 F22 F23 F24 F25 F26 F27 F30 F31 F61
G1 G2 G3 G4 G5 G53
H1 H2 H3 H4 H5 H6 H8 H9 H10
K1 K2 K3s K4s K5 K21s K28 K29s
L1s L2s L5 L6
Q ( 4-6-4-4 and 4-4-6-4):
Articulated steam locomotives:
CC1s CC2s HC1s HH1 HH1s HH2s
Articulated electric locomotives:
AA1 BB1 BB2 BB3 DD1 DD2 FF1 FF2 GG1
E2b E3c E3b E44
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