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.
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.
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.
|Principal Dimensions by Steve Llanso of Sweat House Media|
|Class||200/76||210 / L-77||76 / L-77|
|Railroad||Denver, Northwestern & Pacific (D&SL)||Denver & Salt Lake||Denver & Salt Lake|
|Number in Class||7||7||9|
|Road Numbers||200-209 / 3363-3369||210-216 / 211-216||200-209|
|Locomotive Length and Weight|
|Driver Wheelbase (ft / m)||10.83 / 3.30||10 / 3.05||10 / 3.05|
|Engine Wheelbase (ft / m)||30.67 / 9.35||39.08 / 11.91||39.17 / 11.94|
|Ratio of driving wheelbase to overall engine wheebase||0.35||0.26||0.26|
|Overall Wheelbase (engine & tender) (ft / m)||64.33 / 19.61||72.75 / 22.17||72.75 / 22.17|
|Axle Loading (Maximum Weight per Axle) (lbs / kg)||55,583 / 25,212||55,683 / 25,257|
|Weight on Drivers (lbs / kg)||327,500 / 148,552||333,800 / 151,409||332,000 / 150,593|
|Engine Weight (lbs / kg)||327,500 / 148,552||361,000 / 163,747||362,000 / 164,201|
|Tender Loaded Weight (lbs / kg)||160,000 / 72,575||186,000 / 84,368||176,000 / 79,832|
|Total Engine and Tender Weight (lbs / kg)||487,500 / 221,127||547,000 / 248,115||538,000 / 244,033|
|Tender Water Capacity (gals / ML)||9000 / 34.09||9000 / 34.09||9000 / 34.09|
|Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)||12 / 10.90||12 / 10.90||12 / 10.90|
|Minimum weight of rail (calculated) (lb/yd / kg/m)||91 / 45.50||93 / 46.50||92 / 46|
|Geometry Relating to Tractive Effort|
|Driver Diameter (in / mm)||55 / 1397||55 / 1397||55 / 1397|
|Boiler Pressure (psi / kPa)||225 / 15.50||225 / 15.50||225 / 15.50|
|High Pressure Cylinders (dia x stroke) (in / mm)||20.5" x 32" / 521x813||21" x 32" / 533x813||21" x 32" / 533x813|
|Low Pressure Cylinders (dia x stroke) (in / mm)||33.5" x 32" / 851x813||33.5" x 32" / 851x813||33.5" x 32" / 851x813|
|Tractive Effort (lbs / kg)||68,044 / 30864.28||70,456 / 31958.34||70,456 / 31958.34|
|Factor of Adhesion (Weight on Drivers/Tractive Effort)||4.81||4.74||4.71|
|Firebox Area (sq ft / m2)||206 / 19.14||229 / 21.28||229 / 21.27|
|Grate Area (sq ft / m2)||72.20 / 6.71||72.20 / 6.71||72.20 / 6.71|
|Evaporative Heating Surface (sq ft / m2)||5241 / 486.90||4230 / 393.12||4118 / 382.57|
|Superheating Surface (sq ft / m2)||1046 / 97.21||1249 / 116.03|
|Combined Heating Surface (sq ft / m2)||5241 / 486.90||5276 / 490.33||5367 / 498.60|
|Evaporative Heating Surface/Cylinder Volume||428.73||329.74||321.01|
|Computations Relating to Power Output (More Information)|
|Robert LeMassena's Power Computation||16,245||16,245||16,245|
|Same as above plus superheater percentage||16,245||19,494||19,981|
|Same as above but substitute firebox area for grate area||46,350||61,830||63,376|