Twin Mountain & Potomac 4-6-0 "Ten-Wheeler" Locomotives in the USA

Class Details by Steve Llanso of Sweat House Media

Class 1 (Locobase 13836)

Data from Baldwin Locomotive Works Specification for Engines as digitized by the DeGolyer Library of Southern Methodist University, Volume 39, p. 91. See Larry Smith, "Twin Mountains & Potomac Railroad," Model Railroading (August 1993), pp. 43- at [] and an account at, last accessed 5 February 2012. Works number was 37326 in December 1911.

H L Heintzelman was frustrated with the service available to ship fruit from the orchards at the base of Patterson Creek Mountain to the B & O's St Louis main line at Keyser, some 26 miles distant. So he built this narrow-gauge line to connect the two and opened it on 2 March 1913. 45-lb/yard (22.5-kg/metre) rail, 4% grades, and 30-deg (193-ft/58.8-metre radius) curves indicate the lightness and tightness of this railroad's alignment.

The phstakem entry tells us that during its 6-year existence, the TM & P operated only these two Ten-wheelers and an 0-4-0T dinky (Smith believes the latter was built by Porter). Clearly, Heintzelman intended full service for he provided not only fruit-hauling, but also passenger service in the form of special trains for church meetings. Phstakem also has the lyrics of a song, written to the tune of Casey Jones, describing the day the circus train ran away.

Smith reports that the TM & P never made money and a 1918 peach blight killed most of the crop at the same time orchards lost manpower to the US World War I draft. It closed in February 1919.

Two years after the abandonment, West Virginia bought the 2 in April 1921, operated it for about 5 years, sold it to Gray Lumber Company in October 1926. Sometime later Gray sold the engine to the East Tennessee & Western North Carolina (Tweetsie) as their #8. The Tweetsie operated the 8 until 1939. (Gene Connelly's compilation of all Baldwin production notes that the 1 was scrapped in August 1940, but doesn't identify its owner at the time.)

Principal Dimensions by Steve Llanso of Sweat House Media
Locobase ID13,836
RailroadTwin Mountain & Potomac
Number in Class2
Road Numbers1-2
Number Built2
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)9 / 2.74
Engine Wheelbase (ft / m)18.50 / 5.64
Ratio of driving wheelbase to overall engine wheebase 0.49
Overall Wheelbase (engine & tender) (ft / m)
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)70,500 / 31,978
Engine Weight (lbs / kg)88,500 / 40,143
Tender Loaded Weight (lbs / kg)60,000 / 27,216
Total Engine and Tender Weight (lbs / kg)148,500 / 67,359
Tender Water Capacity (gals / ML)3000 / 11.36
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)6 / 5.50
Minimum weight of rail (calculated) (lb/yd / kg/m)39 / 19.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)45 / 1143
Boiler Pressure (psi / kPa)180 / 12.40
High Pressure Cylinders (dia x stroke) (in / mm)15" x 22" / 381x559
Tractive Effort (lbs / kg)16,830 / 7633.97
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.19
Heating Ability
Firebox Area (sq ft / m2)100 / 9.29
Grate Area (sq ft / m2)14.60 / 1.36
Evaporative Heating Surface (sq ft / m2)1238 / 115.01
Superheating Surface (sq ft / m2)
Combined Heating Surface (sq ft / m2)1238 / 115.01
Evaporative Heating Surface/Cylinder Volume275.13
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation2628
Same as above plus superheater percentage2628
Same as above but substitute firebox area for grate area18,000
Power L15214
Power MT489.14

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Wes Barris