Baltimore & Ohio / Buffalo, Rochester, & Pittsburgh 2-6-6-2 "Mallet Mogul" Locomotives in the USA


Class Details by Steve Llanso of Sweat House Media

Class KK-1 (Locobase 3099)

Like the T-1/T-2 4-8-2 comparison, the KKs were built in single copies to compare the Emerson watertube firebox to a conventional locomotive. This was the EWT entry, works number 61571 in November 1930.

These are the only 2-6-6-2 articulateds the B&O operated other than the BR&P KK-1s (Locobase 295) and are almost unknown today. This engine was converted briefly to a 4-4-6-2 arrangement for passenger service, but soon was restored as a Prairie Mallet and lasted until 1953.


Class KK-2 (Locobase 296)

Data from B&O to 1954 Assorted Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. Works number was 61560 in November 1930.

The 7450 with the conventional stayed firebox was built to compare to the 7400 (Locobase 3099) with an Emerson watertube firebox. In addition to 110 sq ft (10.2 sq m) of heating surface in the combustion chamber, this engine's firebox heating surface at first included 46 sq ft (4.25 sq m) of arch tubes, but the appliance contribution was later revamped with 18 sq ft (1.65 sq m) of arch tubes and 95 sq ft (8.8 sq m) of thermic syphons for a total of 403 sq ft (37.45 sq m).


Class LL / KK-4 (Locobase 295)

Alvin F Staufer & Lawrence W Sagle, B & O Power (1964). Data confirmed by table in May 1916 RME and BR&P 11 - 1930 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. (Thanks to Chris Hohl for pointing out the valve gear IDs on the subclasses.)

These 55 locomotives were built at Alco's Schenectady and Brooks works from 1914 to 1923. All were delivered with 14" (356 mm) piston valves serving the HP cylinders and slide valves supplying the LP cylinders. All but the 7526-7540 batch from Brooks used Walschaert's valve gear. That set of fifteen was equipped with Southern gear.

Several batches delivered as follows, as classified by the B&O and renumbered in 1932:

Works numbers

KK-4 7500-7504 Schenectady 1914 54702-54706

KK-4a 7505-7509 Brooks 1917 57209-57213

KK-4b 7510-7525 Brooks 1918 57996-58011

KK-4c 7526-7540 Brooks 1918 58479-58493

KK-4d 7541-7554 Brooks 1923 64603-64616

One was rebuilt as KK-5 in 1949 with chassis lubrication, bed casting

Retired by 1951.

Specifications by Steve Llanso of Sweat House Media
ClassKK-1KK-2LL / KK-4
Locobase ID3099 296 295
RailroadBaltimore & Ohio (B&O)Baltimore & Ohio (B&O)Buffalo, Rochester, & Pittsburgh (B&O)
CountryUSAUSAUSA
Whyte2-6-6-22-6-6-22-6-6-2
Number in Class1155
Road Numbers74007450700-754 / 7500-7554
GaugeStdStdStd
Number Built1155
BuilderBaldwinBaldwinAlco-Schenectady
Year193019301914
Valve GearWalschaertWalschaertWalschaert or Sthrn
Locomotive Length and Weight
Driver Wheelbase (ft / m)34.92 / 10.6412.17 / 3.7110.33 / 3.15
Engine Wheelbase (ft / m)56 / 17.0755.67 / 16.9749.66 / 15.14
Ratio of driving wheelbase to overall engine wheebase 0.62 0.22 0.21
Overall Wheelbase (engine & tender) (ft / m)104.41 / 31.8286.48 / 26.36
Axle Loading (Maximum Weight per Axle) (lbs / kg)68,000 / 30,844
Weight on Drivers (lbs / kg)372,000 / 168,737373,000 / 169,190367,500 / 166,695
Engine Weight (lbs / kg)465,000 / 210,921466,000 / 211,374445,000 / 201,849
Tender Loaded Weight (lbs / kg)273,000 / 123,831273,000 / 123,831205,600 / 93,259
Total Engine and Tender Weight (lbs / kg)738,000 / 334,752739,000 / 335,205650,600 / 295,108
Tender Water Capacity (gals / ML)18,000 / 68.1818,000 / 68.1812,000 / 45.45
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)20 / 18.2020 / 18.2014 / 12.70
Minimum weight of rail (calculated) (lb/yd / kg/m)103 / 51.50104 / 52102 / 51
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)70 / 177870 / 177857 / 1448
Boiler Pressure (psi / kPa)250 / 17.20250 / 17.20200 / 13.80
High Pressure Cylinders (dia x stroke) (in / mm)23" x 30" / 584x762 (4)23" x 30" / 584x762 (4)23.5" x 32" / 597x813
Low Pressure Cylinders (dia x stroke) (in / mm)37" x 32" / 940x813
Tractive Effort (lbs / kg)96,354 / 43705.4996,354 / 43705.4975,112 / 34070.27
Factor of Adhesion (Weight on Drivers/Tractive Effort) 3.86 3.87 4.89
Heating Ability
Firebox Area (sq ft / m2)866 / 80.48432 / 40.52388 / 36.05
Grate Area (sq ft / m2)92 / 8.5592.30 / 8.5872.20 / 6.71
Evaporative Heating Surface (sq ft / m2)6543 / 608.095471 / 508.464935 / 458.47
Superheating Surface (sq ft / m2)1666 / 154.831698 / 157.811046 / 97.18
Combined Heating Surface (sq ft / m2)8209 / 762.927169 / 666.275981 / 555.65
Evaporative Heating Surface/Cylinder Volume226.77189.62307.20
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation23,00023,07514,440
Same as above plus superheater percentage27,60028,61316,895
Same as above but substitute firebox area for grate area259,800133,92090,792
Power L126,14923,1637772
Power MT929.82821.43279.74

Reference