Denver & Rio Grande Western 2-8-8-8-2/4 "Triplex" Locomotives in the USA

Class Details by Steve Llanso of Sweat House Media

Class Centipede 28 62 62/62 1/4 EEE (Locobase 6823)

(Many thanks to Chris Hohl for his 24 May 2019 email suggesting a different way to characterize the weights of this very unusual design and for noting an incorrect Locobase number reference to the earlier 2-8-8-2s)

In Locobase 3300, we profile the famous Erie P-1s, the helper engines that couldn't boil tea water because the vast capacity of their 6 equal-sized cylinders proved more than a match for the boiler and grate.

In the same year that Erie was testing the Matt Shay, Baldwin prepared a proposal for the Rio Grande. The diagram, preserved in a later diagram book (D&RGW 12 - 1937 Folio 10 supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange), shows a locomotive whose design has been toned down. The cylinders are 2"(50.8 mm) smaller in diameter, but most of the other details were repeated.

This engine's firebox heating surface, which included 108 sq ft (10.03 sq m) of combustion chamber and 88 sq ft of arch tubes, almost matched that of the Erie. The grate itself was deliberately limited to 80 sq ft through a "Gaines wall" such as that used in the 2-8-8-2s (see Locobase 16243), which was expected to raise interior temperatures. In the Erie's, which originally had a similar setup, the Gaines wall was removed when the grate proved much too small. Doubtless the same fix would have been resorted to had this locomotive ever entered service.

Hohl's insight was to understand that although all of the adhesion weight needed to be represented in Locobase's specs, only that portion under the boiler contributed to engine weight, which is how the apparently "upside-down" pair of weights came to be entered.

In the event, the Erie's experience probably dampened enthusiasm and the locomotive was not built.

Principal Dimensions by Steve Llanso of Sweat House Media

ClassCentipede 28 62 62/62 1/4 EEE
Locobase ID6823
RailroadDenver & Rio Grande Western (D&RGW)
Number in Class
Road Numbers
Number Built
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)49.50 / 15.09
Engine Wheelbase (ft / m)71.50 / 21.79
Ratio of driving wheelbase to overall engine wheelbase 0.69
Overall Wheelbase (engine & tender) (ft / m)90 / 27.43
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)720,000 / 326,587
Engine Weight (lbs / kg)805,000 / 365,142
Tender Loaded Weight (lbs / kg)
Total Engine and Tender Weight (lbs / kg)805,000
Tender Water Capacity (gals / ML)9500 / 35.98
Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT)15 / 14
Minimum weight of rail (calculated) (lb/yd / kg/m)100 / 50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)58 / 1473
Boiler Pressure (psi / kPa)210 / 14.50
High Pressure Cylinders (dia x stroke) (in / mm)34" x 32" / 864x813
Low Pressure Cylinders (dia x stroke) (in / mm)34" x 32" / 864x813 (4)
Tractive Effort (lbs / kg)170,769 / 77459.61
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.22
Heating Ability
Tubes (number - dia) (in / mm)290 - 2.25" / 57
Flues (number - dia) (in / mm)48 - 5.5" / 140
Flue/Tube length (ft / m)24 / 7.32
Firebox Area (sq ft / m2)459 / 42.64
Grate Area (sq ft / m2)80 / 7.43
Evaporative Heating Surface (sq ft / m2)6198 / 576.02
Superheating Surface (sq ft / m2)1436 / 133.46
Combined Heating Surface (sq ft / m2)7634 / 709.48
Evaporative Heating Surface/Cylinder Volume184.32
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation16,800
Same as above plus superheater percentage19,992
Same as above but substitute firebox area for grate area114,704
Power L16465
Power MT237.55

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Wes Barris