United States Railroad Administration 4-6-2 "Pacific" Locomotives in the USA


Class Details by Steve Llanso of Sweat House Media

Class Heavy (Locobase 173)

Data from tables in 1930 Locomotive Cyclopedia and from American Locomotive Company, Standardized Locomotives, US Railroad Administration (Alco Pamphlet 10049, 1918), pp. 26-27, reprinted by (Ocean, NJ: Specialty Press , 1973) and DeGolyer, Vol 58, pp. 48+.

See also "Standard Equipment Specialties," Railway Mechanical Engineer, Vol 93, No 3 (March 1919), pp. 137-138 for a list of all the "special equipment" by manufacturers--everything from air brakes to lubricators to rolled steel wheels--and the USRA designs on which they appeared.

Intended to be the standardized Pacific heavy passenger express locomotive, but only twenty were actually allocated by the USRA. The design shared the tube and flue count with two other USRA variants: Light Mikado (Locobase 40) and Light Mountain (Locobase 231). Firebox heating surface included 72 sq ft (6.7 sq m) in the combustion chamber and 28 sq ft (2.6 sq m) in arch tubes. Cylinders were served by piston valves measuring 14" (356 mm) in diameter.

Erie's were built by Alco-Richmond (10) and Baldwin (10) at the direction of the government-run USRA beginning in 1918.


Class Light (Locobase 172)

Data from tables in 1930 Locomotive Cyclopedia and from American Locomotive Company, Standardized Locomotives, US Railroad Administration (Alco Pamphlet 10049, 1918), pp. 24-25, reprinted by (Ocean, NJ: Specialty Press , 1973). See also DeGolyer, Vol 58, pp. 35+ and "Standard Equipment Specialties," Railway Mechanical Engineer, Vol 93, No 3 (March 1919), pp. 137-138 for a list of all the "special equipment" by manufacturers--everything from air brakes to lubricators to rolled steel wheels--and the USRA designs on which they appeared.

This was the "light" Pacific design standardized by the government-run USRA created in World War I and built by Baldwin and Alco. Three railroads actually took delivery of 81 locomotives: Atlantic Coast Lines (28 by Alco-Brooks, 17 by Alco-Richmond), the B&O (20 by Baldwin, 10 by Alco-Richmond), and L&N (6 by Alco-Richmond).

Although described as light, the design in fact had a relatively large grate compared to other engines within its axle-loading range. Firebox heating surface included 46 sq ft (4.3 sq m) in the combustion chamber and 27 sq ft (2.5 sq m) in arch tubes. Cylinders were served by piston valves measuring 14" (356 mm) in diameter.

In the literature describing particular railroads' acquisitions, this design often appears either as the direct-from-USRA variant or a later class based on the USRA Light. And very often, the USRA-inspired 4-6-2 is described as the best, most reliable Pacifics the railroad would own.

Specifications by Steve Llanso of Sweat House Media
ClassHeavyLight
Locobase ID173 172
RailroadUnited States Railroad Administration (USRA)United States Railroad Administration (USRA)
CountryUSAUSA
Whyte4-6-24-6-2
Number in Class
Road Numbers10,00010,000
GaugeStdStd
Number Built
BuilderSeveralSeveral
Year19181918
Valve GearBakerBaker
Locomotive Length and Weight
Driver Wheelbase (ft / m)14 / 4.2713 / 3.96
Engine Wheelbase (ft / m)36.17 / 11.0234.75 / 10.59
Ratio of driving wheelbase to overall engine wheebase 0.39 0.37
Overall Wheelbase (engine & tender) (ft / m)70.70 / 21.5568.62 / 20.92
Axle Loading (Maximum Weight per Axle) (lbs / kg)60,000 / 27,21654,000 / 24,494
Weight on Drivers (lbs / kg)197,000 / 89,358162,000 / 73,482
Engine Weight (lbs / kg)306,000 / 138,799277,000 / 125,645
Tender Loaded Weight (lbs / kg)194,200194,000
Total Engine and Tender Weight (lbs / kg)500,200471,000
Tender Water Capacity (gals / ML)10,000 / 37.8810,000 / 37.88
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)16 / 14.5016 / 14.50
Minimum weight of rail (calculated) (lb/yd)10990
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)79 / 200773 / 1854
Boiler Pressure (psi / kPa)200 / 13.80200 / 13.80
High Pressure Cylinders (dia x stroke) (in / mm)27" x 28" / 686x71125" x 28" / 635x711
Tractive Effort (lbs / kg)43,925 / 19924.0740,753 / 18485.27
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.48 3.98
Heating Ability
Firebox Area (sq ft / m2)327 / 30.39261 / 24.26
Grate Area (sq ft / m2)70.80 / 6.5866.70 / 6.20
Evaporative Heating Surface (sq ft / m2)3824 / 355.393333 / 309.76
Superheating Surface (sq ft / m2)887 / 82.43794 / 73.79
Combined Heating Surface (sq ft / m2)4711 / 437.824127 / 383.55
Evaporative Heating Surface/Cylinder Volume206.09209.52
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation14,16013,340
Same as above plus superheater percentage16,85015,875
Same as above but substitute firebox area for grate area77,82662,118
Power L119,07718,025
Power MT640.47735.89