Northern Pacific 2-8-2 "Mikado" Locomotives in the USA

Class W - superheated (Locobase 12933)

Data from NP 1 - 1929 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange collection; and NP Locomotive Cards supplied in Auguat 2013, also by Allen Stanley.

Locobases 5357 and 30 show the saturated-boiler originals of the first and largest class of Mikados delivered to the NP. The class was soon superheated using a layout identical to that chosen for the slightly later W-2s (Locobase 843), which had larger cylinders.

1609 originally received a Vaughan superheater (a Canadian Pacific-developed Schmidt variant;the NP shops removed it in 194 in favor of a standard Schmidt Type A..

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Class W-1 (Locobase 844)

Follow-ons to the Ws, but fitted with outside Walschaerts valve gear. Initially, they entered service with the boiler pressure set at 150 psi; by 1918, the figure was 180 psi and in 1927, presumably after a reboilering with thicker steel, 200 psi as shown in the specs.

Data confirmed by locomotive diagrams from 1900 hosted on [] (7 Feb 2004). The diagram shows that the last five had Emerson superheaters with one more element and one more flue. Those had a superheater surface area of 570 sq ft.

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Class W-2 (Locobase 843)

Data from NP 1 - 1929 Locomotive Diagrams supplied in May 2005 and NP Locomotive Data Cards pdf supplied in August 2013 by Allen Stanley from his extensive Rail Data Exchange collection.

Delivered as tandem compounds in 1904-1905 (Locobase 13658), these twenty engines were simpled in 1909. They were further rebuilt by the NP's shops with larger cylinders, a combustion chamber, and lower boiler pressures as shown in this entry. NP calculated the cost of each installation at $1,175.

1900 was the first to receive the makeover in July 1911. Procurement of kits for the others was recorded in June-July 1912 (1913-1919) and August 2013 (1901-1912). It's not clear from NP's Locomotive Data cards when the cylinders were bushed to 25", but it seems to happened in the early 1920s. They were supplied steam through the existing 14" (356 mm) piston valves.

Automatic stokers were supplied to firemen in 1924 (who accepted them gratefully, no doubt) at the same time. (Their $2,462.43 cost in 1924 put the expense on a par with the original makeover.)

Worthington feed water heaters were fitted to 1908, 1914-1915, and 1919 in 1928.

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Class W-3 (Locobase 2519)

Data from "Heavy Power for the Northern Pacific," Railway Age Gazette, Volume 55, No. 9 (29 August 1913), pp. 377-378, confirmed by locomotive diagrams from 1900 hosted on [] (7 Feb 2004). By the time this order was completed, according to RAG, the NP had "...in operation 470 locomotives of the 2-8-2 type built by the American Locomotive Company." See also "Extensive Order for New Locomotives for the Northern Pacific Railway Company," Railway and Locomotive Engineering, Vol XXXV, No. 2 (February 1922), pp. 35-36. Works numbers were

1913 March 52849-52876; April 52877-52890, 52892-52897; May 52891, 52898

1917 September 57942-57961

1918 June 58591-58630

1920 November 62442-62466

These enlarged versions of the basic W class showed the effects of superheating on the layout of tubes and flue. Four arch tubes of 3 1/2" diameter supported the firebox's brick arch. They also had outside-frame trailing trucks as well as extended piston rods (ahead of the front of the cylinder) to decrease wear on the bottoms of the pistons and hence the cylinders. Piston valves measured a healthy 16" (406 mm) in diameter. Compared to the Q-5 Pacifics built by Brooks in 1920, these Mikes had slightly larger boilers, but less firebox heating surface.

The diagrams show slight differences among several batches of this large class. RAG reports that the first batch did not have combustion chambers, an omission quickly corrected by Superintendent of Motive Power David Van Alstyne. Still later, W-3s arrived with superheaters already fitted in the boilers. The specifications above represent the W-3 as described in the August 1913 article and reflect the inclusion of both the combustion chamber and the superheater. The 1917 and later engines had 216 tubes, which raised the evaporative heating surface area to 3,634 sq ft (337.6 sq m).

Ten of this class later went to the Spokane, Portland & Seattle as their class O-3. Information from SP&S - 2 1953 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. All of the SP&S Mikes were oil burners. Tenders for all but two held 10,000 US gallons (37,850 litres) of water. 535-537 tenders held 4,300 gallons (16,276 l) of oil, 530 carried 4,100 gallons (15,519 l) of oil, and 531-534's oil capacities came to 4,148 gallons (15,700 l) each.

538-539's tenders sacrificed 700 gallons (2,650 l) of water and held 4,357 gallons (16,491 litres) of oil fuel in addition to 9,300 gallons (35,201 l) of water. These two engines also had four more boiler tubes (216) than the other eight.

NP road number SP&S road number

1702 535

1704 531

1723 537

1726 536

1727 532

1744 533

1747 534

1751 538

1762 539

1765 530

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Class W-4 (Locobase 846)

Data confirmed by locomotive diagrams from 1900 hosted on [] (7 Feb 2004) and NP Locomotive Data Cards supplied in August 2013 by Allen Stanley from his extensive Rail Data Exchange collection. See also "Northern Pacific Converts Prairie Type to Mikado", Railway Age, Volume 67, No 20 ( 14 November 1919, "issued 9 December 1919")), pp. 960-962.

Six rebuilt from T-class 2-6-2s (Locobase 917) in 1918-1919--their original road numbers were 2353, 2363, 2323, 2347, 2322, and 2379, respectively. According to the RA article, the sextet was intended to run between Glendive and Billings, Mont over a relatively gentle 0.5% ruling grade in the westbound direction. The W-4's tonnage rating heading west was 2,600 tons, 62% more than the T class's 1,600 tons. This rise in tonnage rating had the additional benefit of creating a uniformity in tonnage ratings across the NP's sizable 2-8-2 roster, "thus facilitating through movement with out breaking up trains at division points.

They retained their inside link motion, but virtually everything else was changed. Among the least of the alterations was the firebox, which retained its original dimensions except for an 18" (457 mm) addition to the combustion chamber, and very small differences in firebox width. Like the Ts, the W-4's direct heating surface area included 9 sq ft (0.84 sqm) in one arch tube.

The evaporative heating surface grew, largely because the 306 2" tubes of 13 ft 3 in (4.04 m) were replaced by 173 2" tubes and 28 5 1/2" flues measuring 3 ft 3 in(just shy of 1 metre) longer, increasing the EHS by 59 sq ft. Of course, the superheater added more than its measured area; a typical calculation credited each superheater sq ft as 1.5 sq ft equivalent of saturated tube area. Thus, the alteration can be said to granted an additional 730 sq ft (68.82 sq m) to the boiler in the form of drier, more potent steam.

That additional power was fed into 31% more cylinder volume through piston valve that increased 2" in diameter from 12" (305 mm) to 14" (356 mm). Smokebox changes reduced the Ts' problems with throwing sparks, "particularly when used in the district where semi-bituminous coal is burned."

Wheelbase increased substantially with the addition of the fourth driving axle, which resulted in an almost unchanged axle loading in a new cast-steel frame that was 66" (1,676 mm) longer..Axle thickness increased to 10" (254 mm). The result were engines that "ride much easier than the Prairie type and, because of the better weight distribution, are much easier on the track."

W-4s originally entered service supplied by a tender carrying 8,000 US gallons (30,280 litres) of water and 12 tons of coal. It weighed 56,000 lb (25,401 kg) empty and 148,500 lb (67,359 kg) loaded. The renumbered 2500s later pulled the much larger tender shown in the specs.

Later additions included power reverse and a mechanical stoker in 1925.

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Class W-5 (Locobase 847)

Data confirmed by locomotive diagrams from 1900 hosted on [] (7 Feb 2004) and NP to 1944 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange.

Twenty-five engines of considerable power for a Mikado. Most fitted with Elesco or Worthington feedwater heaters. Big 16" (406 mm) valves with 7" (178 mm) travel admitted steam to the nearly square cylinders. The last four were delivered with 55 sq ft (5.1 sq m) of Nicholson thermic syphons.

Drury (1993) cites one 1926 trip in which road number 1844 traveled the 1,898 miles from Seattle to Minneapolis without change pulling a train of unstated weight. During the trip, the locomotive burned 353 tons of coal, boiled 442,000 US gallons (1,672,970 litres) of water and produced 38 tons of ash.

NB: The direct heating surface (including the firebox heating surface) is an estimate calculated by subtracting the calculated tube heating surface from the reported total evaporative heating surface.

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Class W-TAN (Locobase 16368)

Data from "Tandem Compound for the Northern Pacific", Railway Age, Volume 40 , (29 September 1906), p. 392. Works numbers were 30222-30227 in October 1904 and 31121-31134 in July 1905.

After Brooks had delivered 55 simple-expansion W-class locomotives (Locobase 5357), the Dunkirk, NY builder continued the run with this set of 20 tandem compounds. The NP originally numbered them 1550-1569, but changed the series to1600-1619 in 1906, and to the 1900-1919 range later that year.

This relatively short-lived variant of compounding combined in a single casting one high-pressure cylinder in front of a low-pressure cylinder; the engine had two sets, one mounted on each side of the smokebox. In the W-TANs, the HP cylinder received its steam through a 14" (356 mm) piston valve while the LP cylinders took the exhaust through slide valves.

Other than the fitting of tandem compound cylinders, Brooks kept the rest of the W design "without changing any important dimensions back of the cylinders", RA commented. "In fact," the report said, "the distance from the front driving axle to the centerline through the stack and nozzle remains identical."

Whatever the anticipated merits of the tandem compound cylinder, it was soon removed from these engines in favor of the W class's 24" x 30" simple-expansion setup.

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Class W/ WA (Locobase 5357)

Data from "Mikado (2-8-2) Locomotive for the Northern Pacific," Railroad Gazette, Volume XXXVIII, Number 3 (20 January 1905), pp. 50-51; and See also "Locomotive Boilers with Combustion Chambers", Engineering News, Volume LVI [56], No 21 (22 November 1906). See also table in June 1907 AERJ. Works numbers were 30203-30221 in October 1904; 31085-31115 in May 1905; 31116-31120 in June.

First quantity buy of Mikados by any railroad, the 160 ordered by NP had very much a turn-of-the-century look with inside valves and valve gear. Some were built as tandem compounds (in which the 19" high- and 30" low-pressure cylinders were laid out one in front of the other in the same casting; see Locobase 16368.) These first 55 had no combustion chamber and thus had more heating surface area; the firebox heating surface included a mere 8 sq ft (0.74 sq m) in a single arch tube. These first locomotives didn't have combustion chambers, EN reported, but work with the NP's 2-6-2 demonstrated the value of such an addition and later engines had them.

The RG report describes how this class represented a "...return to rational boiler design, more attention having been paid to circulation and effective heating surface than to an effort to obtain the maximum possible heating surface regardless of efficiency." The writer compares this boiler to contemporaneous Santa Fe Mikados and observes how many fewer tubes the NP engine disposes, for example. Also, handling the lightweight lignite fuel used in NP locomotive required a softer draft than most and the engines were delivered with a squat diamond stack and low nozzle in the smokebox.

RG also flagged the suspension for special attention: "A somewhat unusual arrangement of equalizers has been introduced which divides the total weight into two separate units of two drivers and a truck wheel on each side." The preferred "three-legged stool" of the front and rear driver groups and their associated truck came through a coil spring and transverse equalizer bar for the two-wheel trucks at each end

Locobase recommends that those readers interested in the details consult the article, but will note that the pattern of suspension was a spring over each of the axle boxes, each pair of wheels on a side coupled through an underslung equalizer between each two suspended axles.

Soon after their delivery, some of the W's boilers were modified to include a 36" (914 mm) combustion chamber. that added 62 sq ft (5.76 sq m) to the direct heating surface area. This installation was the centerpiece of Mechanical Superintendent David Van Alstyne's program to fit combustion chambers in 70 Mikado and Pacific-type locomotives.

Engineering News's report explained that Van Alstyne sought to "reduce the expenses and troubles (including engine failures) due to leaky tubes, expecially in districts where the engines have to use bad water".)

EN quotes Van Alstyne's conclusion as to the installation's merit, which is worth repeating:"What seems to me an especially good feature ...is the fact that it very materially increases the heating surface of the firebox. The beauty of the combustion chamber is in getting the flues away from the fire." An additional benefit was the ability to work on the flues without having to disturb the frebox's brick arch.

Further development resulted in superheating the entire class; see Locobase 30.

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Class W/ WB (Locobase 30)

Data from table in June 1907 AERJ, confirmed and supplemented by locomotive diagrams from 1900 hosted on [] (7 Feb 2004). ; See also "Locomotive Boilers with Combustion Chambers", Engineering News, Volume LVI [56], No 21 (22 November 1906). (Many thanks to Chris Hohl for his 22 September 2017 email reporting unlikely boiler pressure values for 177 entries. A Locobase macro caused the error.) 39458-39487 in April 1906, 40908-40909 in August, 40910-40931 in September, 40932 in November, 41884-41889 in February 1907, 41890-41923 in March, 42225-42234 in June.

First quantity buy of Mikados by any railroad, the 160 ordered by NP had very much a turn-of-the-century look with inside valves and valve gear. The first 55 had long boiler tubes and no combustion chamber; those are described in Locobase 5357. Beginning with 1555, the boiler was delivered with a 36" (914 mm)-long combustion chamber that led to the shorter boiler tubes shown in the specs as well as 11 sq ft (1.02 sq m) of arch tubes. The addition of 62 sq ft (5.76 sq m) significant jump in direct heating surface area

Alfred W Bruce (The Steam Locomotive in America - Its development in the twentieth century (New York: W W Norton, 1952), pp 296-297) says that these Mikes had about the largest grates that could be hand-fired continuously. Firemen likely found their task feeding this expanse even more demanding than most because of the low-calorie lignite coal the NP often burned. Very few Ws were fitted with automatic stokers before late into their careers.