Denver & Salt Lake / Denver, Northwestern & Pacific Other Articulated Locomotives in the USA


Class Details by Steve Llanso of Sweat House Media

Class 200/76 (Locobase 11471)

Data from "Locomotive Building," The Railway Age Gazette, Vol XLVIII, No 13 (1 April 1910), p. 923. See also "Mallet Engine for the DNW&P," Railway and Locomotive Engineering, Volume 22, No 2 (February 1909), p. 83, and an Excel spreadsheet prepared by Chris Hohl and supplied in a 7 March 2015 email.) Works numbers were 46560-46561 in November 1909 and 48230-48235 in July 1910.

In the long, detailed article on the first engine of this class, the RAG says the DNW&P would be opening a "new field for the Mallet locomotive", a duty that allows the magazine to describe at some length an essential feature of mountain railroading in the winter:

"The engine here illustrated will be used principally as helper and pusher with the rotary snow plows in use on this road ...One of the most essential things in the operation of the rotary snow plow is that it should be handled by as few engines as possible in order that starting and stopping may be done quickly, so as to avoid danger of bucking the plow into a hard packed mass of snow or ice. Heretofore it has been necessary to use as many as five consolidation engines in pushing the rotary during the most severe weather."

So what could the single 200 do that the five smaller engines couldn't?

"It is expected, however, that this Mallet engine, being able to work as slow as four or five miles per hour without danger of stalling. and at its maximum of power, and in fact at an increased power, if necessary, by working it simple, will greatly reduce the number of engines necessary in this kind of service, and so increase the efficiency of the plow."

And an additional benefit: "It must be understood, however, that this engine will also be used in regular road service."

These Mallets didn't remain all-adhesion engines for long. In 1912, the railway, by now renamed Denver & Salt Lake, added a leading truck for better tracking. At the same time, they added a mechanical stoker. See Locobase 6819.

So modified, they served in a helper-engine role until 1947-1952.


Class 210 / L-77 (Locobase 5407)

Data from table in May 1916 RME.

Drury (1993) says that these locomotives were the beneficiaries of two updates to the Mallet design the railroad was already operating -- a leading truck to make it a better road engine and a mechanical stoker.

They apparently served their purpose well because all but one went to the Denver & Rio Grande Western in 1947, from which they retired a few years later (1949-1951) as 3370-3375.


Class 76 / L-77 (Locobase 6819)

Data from D&RGW 1956 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange.

Drury (1993) shows that these started out on the D & SL as 0-6-6-0 Mallets (Locobase 11471) that acquired a leading truck in 1912 to improve their over-the-road qualities. The result was a very uncommon Mallet wheel arrangement in the US. At the same time they were fitted with mechanical stokers. A photo of 200 in 1947 (Drury, p. 162) underscores the short boiler over the engines, even if one mentally deducts the leading truck.

Still the design served its purpose for decades, retiring on the Denver & Rio Grande Western several years after that railroad bought the remaining locomotives in the class in 1947. See the as-built 2-6-6-0s also supplied to the D & SL in 1912 at Locobase 5407.

Specifications by Steve Llanso of Sweat House Media
Class200/76210 / L-7776 / L-77
Locobase ID11,471 5407 6819
RailroadDenver, Northwestern & Pacific (D&SL)Denver & Salt LakeDenver & Salt Lake
CountryUSAUSAUSA
Whyte0-6-6-02-6-6-02-6-6-0
Number in Class779
Road Numbers200-209 / 3363-3369210-216 / 211-216200-209
GaugeStdStdStd
Number Built77
BuilderAlco-SchenectadyAlco-SchenectadyAlco-Schenectady
Year190919131912
Valve GearWalschaertWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)10.83 / 3.3010 / 3.0510 / 3.05
Engine Wheelbase (ft / m)30.67 / 9.3539.08 / 11.9139.17 / 11.94
Ratio of driving wheelbase to overall engine wheebase 0.35 0.26 0.26
Overall Wheelbase (engine & tender) (ft / m)64.33 / 19.6172.75 / 22.1772.75 / 22.17
Axle Loading (Maximum Weight per Axle) (lbs / kg)55,583 / 25,21255,683 / 25,257
Weight on Drivers (lbs / kg)327,500 / 148,552333,800 / 151,409332,000 / 150,593
Engine Weight (lbs / kg)327,500 / 148,552361,000 / 163,747362,000 / 164,201
Tender Loaded Weight (lbs / kg)160,000 / 72,575186,000 / 84,368176,000 / 79,832
Total Engine and Tender Weight (lbs / kg)487,500 / 221,127547,000 / 248,115538,000 / 244,033
Tender Water Capacity (gals / ML)9000 / 34.099000 / 34.099000 / 34.09
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)12 / 10.9012 / 10.9012 / 10.90
Minimum weight of rail (calculated) (lb/yd / kg/m)91 / 45.5093 / 46.5092 / 46
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)55 / 139755 / 139755 / 1397
Boiler Pressure (psi / kPa)225 / 15.50225 / 15.50225 / 15.50
High Pressure Cylinders (dia x stroke) (in / mm)20.5" x 32" / 521x81321" x 32" / 533x81321" x 32" / 533x813
Low Pressure Cylinders (dia x stroke) (in / mm)33.5" x 32" / 851x81333.5" x 32" / 851x81333.5" x 32" / 851x813
Tractive Effort (lbs / kg)68,044 / 30864.2870,456 / 31958.3470,456 / 31958.34
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.81 4.74 4.71
Heating Ability
Firebox Area (sq ft / m2)206 / 19.14229 / 21.28229 / 21.27
Grate Area (sq ft / m2)72.20 / 6.7172.20 / 6.7172.20 / 6.71
Evaporative Heating Surface (sq ft / m2)5241 / 486.904230 / 393.124118 / 382.57
Superheating Surface (sq ft / m2)1046 / 97.211249 / 116.03
Combined Heating Surface (sq ft / m2)5241 / 486.905276 / 490.335367 / 498.60
Evaporative Heating Surface/Cylinder Volume428.73329.74321.01
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation16,24516,24516,245
Same as above plus superheater percentage16,24519,49419,981
Same as above but substitute firebox area for grate area46,35061,83063,376
Power L13962934410,427
Power MT160.03370.28415.44