Western Maryland 4-8-4 "Northern" Locomotives of the USA

The Western Maryland Railroad pooled motive power with the Reading Railroad and when the Reading started using its new Class T-1s running times were improving on the Allentown, PA to Hagerstown, MD freight trains. This caught the attention of the Western Maryland and in 1947 it took delivery of twelve 4-8-4s from the Baldwin Locomotive Works. Being a "southern" railroad WM rejected the name "Northern" and called its 4-8-4s "Potomacs".

These twelve Class J-1 "Potomacs" (road numbers 1401 through 1412) were designed for freight service with 69" drivers, 26.5 x 32 cylinders, a boiler pressure of 255 psi, a weight of 506,500 pounds and a tractive effort of 70,600 pounds.

All were taken out of service by the end of May 1954 and placed in storage in Hagerstown and Cumberland. They were not sold for scrap until the equiment trusts ran out in 1957.

Class Details by Steve Llanso of Sweat House Media

Class J-1 (Locobase 286)

Data from 1947 Locomotive Cyclopedia, supplemented by WM Misc Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection. Works numbers were 73082-73093 in January 1947.

Firebox heating surface included 153 sq ft in 4 thermic syphons in the firebox proper as well as in the combustion chamber. Known as "Potomacs," these engines had very nearly the same performance at 45 mph as the M-2 class 4-6-6-4s. They were the last 4-8-4s built new for a railroad in the US and retired with the rest of Western Maryland's steam in 1954.

Specifications by Steve Llanso of Sweat House Media
Locobase ID286
RailroadWestern Maryland (WM)
Number in Class12
Road Numbers1401-1412
Number Built12
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft)19.25
Engine Wheelbase (ft)46.83
Ratio of driving wheelbase to overall engine wheebase 0.41
Overall Wheelbase (engine & tender) (ft)95
Axle Loading (Maximum Weight per Axle) (lbs)72,500
Weight on Drivers (lbs)290,000
Engine Weight (lbs)506,500
Tender Loaded Weight (lbs)421,500
Total Engine and Tender Weight (lbs)928,000
Tender Water Capacity (gals)22,000
Tender Fuel Capacity (oil/coal) (gals/tons)30
Minimum weight of rail (calculated) (lb/yd)121
Geometry Relating to Tractive Effort
Driver Diameter (in)69
Boiler Pressure (psi)255
High Pressure Cylinders (dia x stroke) (in)26.5" x 32"
Tractive Effort (lbs)70,591
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.11
Heating Ability
Firebox Area (sq ft)573
Grate Area (sq ft)106.70
Evaporative Heating Surface (sq ft)4973
Superheating Surface (sq ft)2170
Combined Heating Surface (sq ft)7143
Evaporative Heating Surface/Cylinder Volume243.44
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation27,209
Same as above plus superheater percentage35,371
Same as above but substitute firebox area for grate area189,950
Power L139,288
Power MT1194.69



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