Missouri Pacific / Saint Louis, Iron Mountain & Southern 4-8-0 "Mastodon" Locomotives of the USA

Class Details by Steve Llanso of Sweat House Media

Class 1801 - superheated (Locobase 2811)

Data from MP 7 - 1956 locomotive diagram book supplied in May 2005 by Allen Stanley from his extensive Raildata collection.

See Locobase 6651 for the original saturated-boiler variant.

Drury (1993) notes that their small drivers meant speeds so low that they were useful to yard service. Yet this limitation didn't prevent the railroad from superheating the lot and adding firebox appliances. Such superheating came well after 1901 and the 56 sq ft (5.2 sq m) of thermic syphons in the firebox and a feedwater heater later still.

Class TW-55 (Locobase 6651)

Data from 1924 MP locomotive diagram book supplied in May 2005 by Allen Stanley from his extensive Raildata collection. Brooks builder info from B.Rumary, 25 Kingscombe, Gurney Slade, Radstock, BA3 4TH, ENGLAND and Jeremy Lambert as supplied by Allen Stanley in March 2004. Works #4022-4027 (November 1901). As an Alco division, Brooks delivered the other 13 in 1903.

As Drury (1993) notes, "They were typically Brooks 4-8-0s, with Belpaire fireboxes, inside valves, Stephenson valve gear, and 55" drivers." The drivers were so small on this large-scale engine that the Belpaire boiler showed a huge amount of daylight. Used between De Soto and Piedmont, Missouri over the Gads Hill and Mineral Point grades as helpers, they came into the Missouri Pacific as TW-55

They were always too slow for most main-line freight service, so the class soon went into switching service. In the 1920s, the railroad fitted a longer main rod to drive the third axle. Drury says that this introduced complications in counter-balancing, but at switching speeds there was little impact.

Some time in the class's career, they were superheated. Locobase 2811 shows the result.

Specifications by Steve Llanso of Sweat House Media
Class1801 - superheatedTW-55
Locobase ID2811 6651
RailroadMissouri Pacific (MP)Saint Louis, Iron Mountain & Southern (MP)
Number in Class1919
Road Numbers1801-18171201-1219 / 1801-1819
Number Built19
Valve GearStephensonStephenson
Locomotive Length and Weight
Driver Wheelbase (ft)12.3315.50
Engine Wheelbase (ft)25.33
Ratio of driving wheelbase to overall engine wheebase 0.61
Overall Wheelbase (engine & tender) (ft)57.19
Axle Loading (Maximum Weight per Axle) (lbs)
Weight on Drivers (lbs)183,400172,000
Engine Weight (lbs)233,000208,200
Tender Loaded Weight (lbs)118,400
Total Engine and Tender Weight (lbs)326,600
Tender Water Capacity (gals)6000
Tender Fuel Capacity (oil/coal) (gals/tons)10
Minimum weight of rail (calculated) (lb/yd)7672
Geometry Relating to Tractive Effort
Driver Diameter (in)5555
Boiler Pressure (psi)190190
High Pressure Cylinders (dia x stroke) (in)21" x 32"21" x 32"
Tractive Effort (lbs)41,43841,438
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.43 4.15
Heating Ability
Firebox Area (sq ft)272206
Grate Area (sq ft)61.8062.20
Evaporative Heating Surface (sq ft)28733333
Superheating Surface (sq ft)550
Combined Heating Surface (sq ft)34233333
Evaporative Heating Surface/Cylinder Volume223.96259.82
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation11,74211,818
Same as above plus superheater percentage13,62111,818
Same as above but substitute firebox area for grate area59,94939,140
Power L112,4685924
Power MT599.50303.72


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