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

The Denver & Rio Grande Western Railroad took delivery of its first ten "Mountains" (road numbers 1501 through 1510) from the American Locomotive Company in 1922. These Class M-67 locomotives had 28 x 30 cylinders, 63" drivers, a boiler pressure of 210 psi, a tractive effort of 66,640 lbs and a weight of 377,000 pounds.

Ten more "Mountains" (road numbers 1511 through 1520) came in 1923. They were designated Class M-78 and were equipped with boosters which increased their tractive effort to 78,967 pounds. They were identical to the Class M-67 locomotives except for the boosters and an increase in total weight of 7,200 pounds. A second batch of ten Class M-67s (road numbers 1521 through 1530) came from ALCO in 1923 and were similar to the 1922 Class M-67s except for an increase of 1,600 lbs in total weight.

A final ten (road numbers 1600 through 1609) came from the Baldwin Locomotive Works in 1926 and were designated as Class M-75. These M-75s had three 25" dia. x 30" stroke cylinders, 67" dia. drivers, a boiler pressure of 210 psi, a tractive effort of 74,970 lbs and weighed 419,300 pounds. All forty of these D&RGW "Mountains" were dismantled between 1948 and 1955.


Roster

ClassRoad NumberYear BuiltBuilder
M-671501-15101922ALCO
M-781511-15201923ALCO
M-671521-15301923ALCO
M-751600-16001926Baldwin

Class Details by Steve Llanso of Sweat House Media

Class 14-34 1/4 E - proposal (Locobase 6822)

Data from D&RGW 12 - 1937 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. (Thanks to Chris Hohl for his 13 August 2020 email suggesting adding the word "proposal" to the designation of this engine and the same year as 6821 in the Year Built field.)

Locobase doesn't know for sure, but believes this, like Locobase 6821, is a proposal submitted to the D&RGW in the 1920s in response to an inquiry about a narrow-gauge Mountain engine. Chris Hohl determine this proposal was drafted in January 1925. Neither was built, probably because the railway was phasing out narrow-gauge operations.


Class 14-36 1/4 E - proposal (Locobase 6821)

Data from D&RGW 12 - 1937 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange.

Locobase doesn't know for sure, but believes this is a proposal submitted to the D&RGW in the 1920s in response to an inquiry about a narrow-gauge Mountain engine; Locobase 6822 shows a smaller version. Neither was built, probably because the railway was phasing out narrow-gauge operations. This design compares well to other narrow-gauge Mountain designs in Locobase (most of which were sized to the Cape Gauge of 42"). It has a lot of boiler for the cylinder volume, a useful degree of superheat, and reasonably tall drivers


Class M-67 (Locobase 1344)

Data from 1937 D & RGW locomotive diagram book supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. See also"Most Powerful Passenger Locomotive in the World", Railway and Locomotive Engineering, Volume , No 12 (December 2022), pp. 323-325 ; Powerful Mountain Type Locomotives--Denver and Rio Grande Western Railway", Railway Journal, Volume , Volume 22 No 10 (October 1922), p.18; and "4-8-2 Type Locomotive for the Denver and Rio Grande Western Railroad", Engineering, Volume CXVI [116] (6 July 1923), pp. 26- (Thanks to Chris Hohl for his 24 November 2023 email correcting the driver diameter, supplying tender weight and original capacity. Works numbers were 63307-63316 in June 1922 and 64288-64696 in June 1923.

When built, the railroad press described the class as the largest passenger locomotives in the world.. They were the Rio Grande's first Mountains. Delivered three batches, all ran on unusually small 63" drivers to maintain an average higher speed over the railroad's challenging grades while hauling trains that normally required two Mountain types. .Tackling the severe curvature of even the main lines dictated the use of a floating front axle with spherical bushes that reduced the fixed driving wheelbase to 11 ft 2 in (3.40 m). 1501-1510 and 1521-1530 were identical; 1511-1520 had a booster engine mounted on the trailing truck and were designated M-78; these ran Grand Junction to Denver..

M-67s consumed 8,,000 gallons (30,280 litres) of water and 5 1/2 tons (5 metric tons) of coal per hour. A Duplex stoker significantly improved the fireman's lot. Firebox heating surface area amounted to 368 sq ft (34.19 sq m), of which five arch tubes contributed 35 sq ft (3.25 sq m) .. Later heating aids included thermic syphon adding 92 102 sq ft (8.55-9.48 sq m), but reducing arch tube area to 21 sq ft (1.95 sq m). Direct heating surface consequently grew to 456 sq ft (42.36 sq m), and total evaporative heating surface climbed to 4,698 sq ft (436.36 sq m) when fitted with the most syphons. A combustion chamber and, later, an Elesco feed water heater further enhanced the incoming water's willingness to steam.

R&LE pays particular attention to the trailing truck's Delta truck produced by Commonwealth Steel of St Louis. Their leading paragraph on this subject summarizes the economic and efficient truck design: "This truck combines in a single casting the radius bar members, journal box guides, end transom and equalizer pivot." Loaded at three points ("two at the rear and the third at the front end center pivot"), the truck used a separate equalizer made the truck "particularly easy riding." Considering its role in supporting the entire firebox and negotiating curves, such praise suggests a successful design.

The tender came in for its own extended analysis because of its great capacity and loaded weight, which Chris Hohl reports came to 267,600 lb (121,381 kg). While tankage didn't change, the tender's original 20 ton coal capacity later increased to the 25 tons shown in the specs.

Such large capacities and the locomotives' general level of quality, reported Engineering, meant these engines could haul expresses the full 302 miles running south and west of Denver to Minturn without a change. (Simple math suggests at least two, probably three water stops, however.). As Railway Journal pointed out, however, their specific remit was "service on the mountain divisions ...between Salida ...and Minturn." in which they crossed the Continental Divide at 10,240 ft (3,121 m) , the highest point on a transcontinental railroad.

Except for two scrapped in the latter half of 1949, the three batches served the D&RGW for three decades, before their retirements in 1950-1955.


Class M-75 (Locobase 204)

Dat afrom D&RGW 12 - 1937 FOLIO 10 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. See also DeGolyer, Volume 76, p. 299. Works numbers were 59240-59244 in May 1925 and 59293-59295, 59336-59337 in July.

These dual-service locomotives used three cylinders. Drury (1993) comments: "Their construction by Baldwin is something of a curiosity. They constitute five-sixths of Baldwin's three-cylinder production; and Brooks, which had built D&RGW's two-cylinder Mountains, was the chief advocate of three-cylinder power."

As delivered, the firebox had a combustion chamber offering 120 sq ft (11.15 sq m) of heating surface area, 25 sq ft (2.3 sq m) in arch tubes, and 85.5 sq ft (7.95 sq m) of Nicholson thermic syphons in the firebox only. (The two syphons and three arch tubes supported the brick arch.) Locobase notes the big-tube layout that included 2 1/4" tubes and more than five dozen 5 1/2" flues.

The first five engines had Worthington #4 feed water heaters; the last five were fitted with Elescos.. Each of the cylinders was supplied through a 12" (305 mm) piston valve.

The railway would later modify the firebox by deleting the arch tubes and increasing the thermic syphon area to 96 sq ft (8.9 sq m). At that point, the combustion chamber accounted for 100 sq ft (9.3 sq m) of direct heating surface, which now totalled 498 sq ft (46.25 sq m). Also, the boiler gained three heating tubes and somehow added 75 sq ft of superheater area even though the flue count and length remained the same. (Perhaps the elements themselves had slightly greater diameters or lengths within the flues.)

Using three cylinders on a locomotive burning low-calorie, semi-bituminous Rosebud coal seems an odd choice. Even though each cylinder was smaller the total cylinder volume was greater than a comparable two-cylinder locomotive. Apparently the firebox and boiler were big enough and the railway was apparently satisfied enough to maintain the design's three-cylinder layout until retirement in the late 1940s.

1601 was dismantled in December 1941 for some reason; the next to go was 1604 in March 1948 and the last was 1607 in November 1949.

Principal Dimensions by Steve Llanso of Middle Run Media

Class14-34 1/4 E - proposal14-36 1/4 E - proposalM-67M-75
Locobase ID6822 6821 1344 204
RailroadDenver & Rio Grande Western (D&RGW)Denver & Rio Grande Western (D&RGW)Denver & Rio Grande Western (D&RGW)Denver & Rio Grande Western (D&RGW)
CountryUSAUSAUSAUSA
Whyte4-8-24-8-24-8-24-8-2
Number in Class3010
Road Numbers1501-15301600-1609
Gauge3'3'StdStd
Number Built3010
BuilderBaldwinBaldwinAlco-BrooksBaldwin
Year192519221925
Valve GearWalschaertWalschaertWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)13 / 3.9613.75 / 4.1917.25 / 5.2618.25 / 5.56
Engine Wheelbase (ft / m)31.17 / 9.5031.92 / 9.7339.83 / 12.1441.50 / 12.65
Ratio of driving wheelbase to overall engine wheelbase 0.42 0.43 0.43 0.44
Overall Wheelbase (engine & tender) (ft / m)60.25 / 18.3661.17 / 18.6482.23 / 25.0686.41 / 26.34
Axle Loading (Maximum Weight per Axle) (lbs / kg)64,500 / 29,25773,130
Weight on Drivers (lbs / kg)138,000 / 62,596142,000 / 64,410257,500 / 116,800290,530 / 131,782
Engine Weight (lbs / kg)181,000 / 82,100199,000 / 90,265377,000 / 171,005419,310 / 190,196
Tender Loaded Weight (lbs / kg)106,000 / 48,081106,000 / 48,081277,600 / 125,917291,000
Total Engine and Tender Weight (lbs / kg)287,000 / 130,181305,000 / 138,346654,600 / 296,922710,310
Tender Water Capacity (gals / ML)5000 / 18.945000 / 18.9414,000 / 53.0315,000 / 56.82
Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT)8 / 78 / 725 / 2325 / 23
Minimum weight of rail (calculated) (lb/yd / kg/m)58 / 2959 / 29.50107 / 53.50121 / 60.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)44 / 111848 / 121963 / 160067 / 1702
Boiler Pressure (psi / kPa)190 / 13.10190 / 13.10210 / 14.50210 / 14.50
High Pressure Cylinders (dia x stroke) (in / mm)20" x 24" / 508x61021" x 24" / 533x61028" x 30" / 711x76225" x 30" / 635x762 (3)
Tractive Effort (lbs / kg)35,236 / 15982.8035,611 / 16152.9066,640 / 30227.4374,930 / 33987.72
Factor of Adhesion (Weight on Drivers/Tractive Effort) 3.92 3.99 3.86 3.88
Heating Ability
Tubes (number - dia) (in / mm)110 - 2.25" / 57131 - 2.25" / 57220 - 2.25" / 57244 - 2.25" / 57
Flues (number - dia) (in / mm)21 - 5.5" / 14028 - 5.5" / 14058 - 5.5" / 14064 - 5.5" / 140
Flue/Tube length (ft / m)19.50 / 5.9420 / 6.1020 / 6.1019.50 / 5.94
Firebox Area (sq ft / m2)144 / 13.38154 / 14.31425 / 39.48512 / 47.58
Grate Area (sq ft / m2)40.20 / 3.7442.70 / 3.9780.20 / 7.4595 / 8.83
Evaporative Heating Surface (sq ft / m2)2155 / 200.282495 / 231.884667 / 433.575094 / 473.33
Superheating Surface (sq ft / m2)505 / 46.93707 / 65.711333 / 123.841495 / 138.94
Combined Heating Surface (sq ft / m2)2660 / 247.213202 / 297.596000 / 557.416589 / 612.27
Evaporative Heating Surface/Cylinder Volume246.85259.36218.29199.22
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation7638811316,84219,950
Same as above plus superheater percentage9089989820,54724,539
Same as above but substitute firebox area for grate area32,55835,697108,885132,250
Power L111,84315,21319,37819,359
Power MT756.79944.76663.63587.61

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