Northern Pacific 4-6-2 "Pacific" Locomotives

Class Details by Steve Llanso of Sweat House Media

Class Q (Locobase 917)

Data from table in AERJ July 1903.

Firebox heating surface included 22.9 sq ft of arch tubes. Drury (1993) notes that these were among the first Pacifics anywhere and that they set the tone for the next several batches. A note on the Q diagram hosted at the NP Research site (, last accessed 25 April 2008) shows that the first 7 were delivered with piston valves, the next 8 with slide valves, and the last with Davis counter-balanced slide valves.

Most retired by World War II.

Class Q-1 (Locobase 918)

Data from table in June 1906 AERJ.

According to Drury (1993), these engines differed from the Qs in having larger boilers with a noticeable taper, outside frames on the trailing trucks, and 20,000 lb more engine weight. 2100-2105 were built in 1904, 2106-2117 in 1905.

Class Q-2 (Locobase 919)

Data from NP TO 1944 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection.

Firebox heating surface included 8.9 sq ft of arch tubes. Built as Cole balanced compounds in 1906 and celebrated as such in Railway Age, these engines had inside admission for the high-pressure piston valves, outside for the low-pressure ones. One advantage claimed for the 4-cylinder compound was the reduction of hammer-blow on the rails. Also, tests suggested an increase in horsepower through compounding without an increase in boiler size.

Obviously, these advantages either were illusory or not worth the trouble as these engines were rebuilt as simple-expansion types in 1909. See Q-3, Q-4 for results.

Class Q-3 (Locobase 920)

Data confirmed by locomotive diagrams from 1900 hosted on (7 Feb 2004). Baldwin's share ran from 2148 to 2157 (works numbers were 33248-33251, 33277-33282 in March 1909). (6 June 2005) says that the Q-3s operated primarily on the St. Paul-Duluth section although some were assigned to the North Coast Limited between Livingston and Butte, Montana.

According to the museum, "They were well-liked by the crews, capable of cruising at 95 mph."

But see Locobase's assessment of that claim at entry 6568, the superheated upgrade

Class Q-3 (Locobase 2804)

Data from NP TO 1944 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection.

Three of the Q-3s had larger cylinders, added after they came on the road. Two of these were part of the 10-locomotive batch supplied by Baldwin, the other came from Alco-Schenectady's delivery.

See Locobase 920 for more information and 6568 for the superheated upgrade.

Class Q-3 - superheated (Locobase 6568)

Data from Form 7310 specification/improvement card available on (visited 6 June 2005).

This is the superheated version of all converted Q-3 Pacifics (see Locobase 920 & 2804). According to the spec card, 8 sq ft of firebox heating surface was represented by an arch tube. Steam admission came through 12" piston valves.

An early example of superheating an existing design, this class had a relatively low degree of superheat. A somewhat unusual result of the exercise was a boiler still pressed to the original psi (many such conversions would reduce pressure) and containing more combined heating surface than before.

Locobase skeptically repeats a comment from 920 because it seems more likely with the superheated version: "They were well-liked by the crews, capable of cruising at 95 mph."

Locobase thinks that's a pretty high speed for 69" drivers. At that pace, they were whirling around at 463 rpm and the piston speed topped 2,000 fpm. And while the ratio between heating surface and cylinder volume runs toward the higher end of similar locomotives, it wasn't the highest.

Class Q-4 (Locobase 923)

Data confirmed by locomotive diagrams from 1900 hosted on (7 Feb 2004).

This set of Q-4s were Baldwin's supplement to the Q-3s. All were produced in 1909: 33568-

33569, 33588-33591 in July; 33619, 33622-33627 in August; 33796-33797, 33847-33850 in September; 33888-33891, 33919-33923, 33944 in October; 33971, 34079-34083 in November; and 34110-34112, 34118-34119, 34136-34137, 34143-34144 in December. The last two months' of production featured cylinders bored out to 24 1/2". Some of these were later relined to reduce the bore to 23".

A few were rebored to 24 1/2"

Class Q-4 (Locobase 2805)

Alco versions of the larger-cylinder Q-3s. Data confirmed by locomotive diagrams from 1900 hosted on (7 Feb 2004).

Further supplemented by reproduction of 1913 Alco Bulletin 1016 on Richard Leonard's (accessed 16 June 2006). Firebox heating surface included 8 sq ft of arch tubes. Note how low (14.1%) is the superheat ratio, indicative of how early in the era this design was produced.

In Northern Pacific's Tell Tale (June, 1950) (, R. V. Nixon gave the following account of the Q-4 2222.




Yes, that's a lot of deuces. but this train order actually was issued on the Rocky Mountain Division when Q-4 engine 2222 was assigned to [T]rains 221 and 222.

The four deuces has had a strenuous career with the N.P. Built by the Schenectady Works of ALCO in 1910, the 2222 was assigned immediately to the North Coast Limited out of Missoula, in which service it remained for nearly 15 years. It was a rugged job. Many enginemen will recall the scenic, but back-breaking run on No. 2 from Paradise to Missoula in the pre-stoker days. It took a first class fireman to keep a full head of steam on the steadily ascending grade from Paradise to Evaro, even though a helper was added at Arlee for the tough 2.2 [percent] grade to the top of the mountain. Needless to say, the 2222 worked at full capacity for the entire distance.

Quite a contrast to the effortless manner in which the present day Diesel-powered No. 2 slithers from Paradise to Evaro, almost oblivious of any climb. But we doubt if a Diesel could present anything as breath-taking and dramatic as the old 2222 barreling around a curve along the Pend d'Oreille River, throttle wide open, rods flashing in the sunlight, and the sharp exhaust emitting a plume of smoke into the clear, mountain air.

On the 50th anniversary of the North Coast Limited it is interesting to note that Q-4 power was standard on the train for a longer period than any other class of locomotive. The N.P. purchased a total of 49 Q-4s from Baldwin and Alco. Of these, 25 still remain in service, including the 2222 which is now taking it easy as a protection engine at Spokane

Class Q-5 (Locobase 925)

Data from "Heavy Power for the Northern Pacific," Railway Age Gazette, Volume 71, No. 17 (22 October 1929), pp.767-769, confirmed and supplemented by NP TO 1944 Locomotive Diagram book supplied in May 2005 by Allen Stanley from his extensive Raildata collection.

4 arch tubes of 3 1/2" diameter supported the firebox's brick arch; these contributed 35 sq ft to the firebox's heating surface. 14" piston valves supplied steam to the cylinders.

According to Drury (1993) these twenty engines were designed to weigh 296,000 lb with no more than 62,500 lb on an axle. They were also to cost no more than current engines of similar size. A year after their delivery, RAG explained that they were intended for the Dilworth, Minn -Missoula, Mont. section of the road, which included 2.3% grades and 16-deg curves. On that section, the Q-5 would have 12-car trailing load with 17-car trains not unheard of. RAG claimed that weight on the drivers came to 181,000 lb and total engine weight to 314,000 lb. RAG calculated that these engines developed their maximum horsepower at 46.5 mph.

Drury contends that when Brooks delivered the Q-5s in 1920, however, axle load had grown to 65,433 lb, total weight to 323,700 lb and the price to $70,916. Also, they were seen as more complicated and harder to maintain. Variable-lead valve gear proved so daunting to adjust at first that the NP set the maximum speed at 55 mph, considerably less than hoped. NP soon worked out the bugs and the railroad ordered another 20 as Q-6s.

Class Q-6 (Locobase 926)

Data from "Extensive Order for New Locomotives for the Northern Pacific Railway Company," Railway and Locomotive Engineering, Vol XXXV, No. 2 (February 1922), pp. 35-36. Data confirmed by locomotive diagrams from 1900 hosted on (7 Feb 2004).

2261-2265 differed only in the use of oil as a fuel; they had 3,500-gal oil capacity tenders. Six (2252-2257) had 11,000-lb boosters.

Diagram shows 14" (356 mm) diameter piston valves. RLE noted that Brooks welded the boiler seams instead of riveting and formed the crown and side sheets as a single piece (which obviated either welding or riveting). The combustion chamber also consisted of one piece of steel that was butt-welded along the bottom and to the crown sheet at the top. The entire frame, save for the tender, was made of cast steel.

Locobase likes to reproduce the "specialty" suppliers when he encounters such a list as it portrays the network of components and companies that contributed to steam-locomotive manufacture in the US. For these Pacifics, RLE reported the following:

American Arch Co.'s brick arch in five sections, supported on four 3 1/2 in. tubes

coal pusher on tender

Franklin Railway Supply Co.'s No. 8 butterfly fire-door

Commonwealth Steel Co.'s cradle at rear of frames

Hunt-Spiller gun iron cylinder and valve chamber bushings

cylinder cocks operated by Hancock pneumatic operating cylinders

driving axles-hammered open-hearth, oil heat treated steel-hollow bored

Elvin grease cellars

Hancock non-lifting injectors

Pyle National back-up lamp

Adams & Westlake marker lamps equipped with tungsten marker lamps

Hancock line checks and strainers

Detroit lubricators

Ohio Injector Company's Chicago flange lubricators on front drivers

Adreon-Campbell graphite lubricators

Hancock guide oil cups

Brunker force feed air piping attachment connected to oil supply pipes between sight feed and air cylinder of compressor

King type U. S. metallic packing on piston rods and valve stem

Wilbert grease lubricators on piston rods

Mellin reverse gear with oil piston

Barco automatic smoke box blower fittings

double sanders equipped with Viloco duplex sander valve

three 3 1/2 in. Consolidated safety valve with the encased pops

balanced throttle valve top opening with drifting valve in dome

Hancock 2 l/2 in. double vertical check valve with double stop valve

Smith adjustable hub liners on all driving wheels

Smith adjustable hub plates on trailing truck wheels

Specifications by Steve Llanso of Sweat House Media
ClassQQ-1Q-2Q-3Q-3Q-3 - superheatedQ-4Q-4Q-5Q-6
Locobase ID917 918 919 920 2804 6568 923 2805 925 926
RailroadNorthern Pacific (NP)Northern Pacific (NP)Northern Pacific (NP)Northern Pacific (NP)Northern Pacific (NP)Northern Pacific (NP)Northern Pacific (NP)Northern Pacific (NP)Northern Pacific (NP)Northern Pacific (NP)
Road Numbers2080-20992100-21472175-21762148-21702153, 2161, 216921562177-22072208-22252226-22452246-2265
Valve GearStephensonStephensonWalschaertWalschaertWalschaertWalschaertWalschaertWalschaertWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase12'12'12'12'12'12'12'12'14'13.17'
Engine Wheelbase33'32.50'33.41'32.50'32.50'32.50'32.50'32.50'35.59'36.75'
Ratio of driving wheelbase to overall engine wheebase 0.36 0.37 0.36 0.37 0.37 0.37 0.37 0.37 0.39 0.36
Overall Wheelbase (engine & tender)58.37'62.04'62.83'61.92'71.30'
Axle Loading (Maximum Weight per Axle)53800 lbs65433 lbs64100 lbs
Weight on Drivers134000 lbs142500 lbs157000 lbs150000 lbs150000 lbs146200 lbs155100 lbs155100 lbs196300 lbs199900 lbs
Engine Weight202000 lbs219000 lbs380500 lbs236000 lbs236000 lbs236000 lbs244400 lbs237000 lbs318900 lbs323900 lbs
Tender Light Weight123400 lbs128500 lbs141350 lbs141350 lbs141350 lbs141350 lbs145300 lbs145300 lbs199600 lbs198500 lbs
Total Engine and Tender Weight325400 lbs347500 lbs521850 lbs377350 lbs377350 lbs377350 lbs389700 lbs382300 lbs518500 lbs522400 lbs
Tender Water Capacity6000 gals6000 gals7000 gals7000 gals7000 gals7000 gals7000 gals7000 gals10000 gals10000 gals
Tender Fuel Capacity (oil/coal)12 tons12 tons12 tons12 tons12 tons12 tons12 tons12 tons14 tons14 tons
Minimum weight of rail (calculated) on which locomotive could run74 lb/yard79 lb/yard87 lb/yard83 lb/yard83 lb/yard81 lb/yard86 lb/yard86 lb/yard109 lb/yard111 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter69"69"69"69"69"69"69"69"73"73"
Boiler Pressure200 psi200 psi220 psi200 psi200 psi200 psi200 psi200 psi200 psi200 psi
High Pressure Cylinders (dia x stroke)22" x 26"22" x 26"16.5" x 26"22" x 26"24.5" x 26"22" x 26"23" x 26"24.5" x 26"26" x 28"26" x 28"
Low Pressure Cylinders (dia x stroke)27.5" x 26" (2)
Tractive Effort31004 lbs31004 lbs28211 lbs31004 lbs38451 lbs31004 lbs33887 lbs38451 lbs44079 lbs44079 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.32 4.60 5.57 4.84 3.90 4.72 4.58 4.03 4.45 4.54
Heating Ability
Firebox Area198.20 sq. ft188.40 sq. ft241.80 sq. ft242 sq. ft242 sq. ft241 sq. ft250 sq. ft240 sq. ft335 sq. ft335 sq. ft
Grate Area47.20 sq. ft43.50 sq. ft43.50 sq. ft43.50 sq. ft43.50 sq. ft43.50 sq. ft43.50 sq. ft43.50 sq. ft70.30 sq. ft70.30 sq. ft
Evaporative Heating Surface3463 sq. ft3549 sq. ft2909 sq. ft2926 sq. ft2926 sq. ft2620 sq. ft2450 sq. ft2455 sq. ft3419 sq. ft3461 sq. ft
Superheating Surface444 sq. ft391 sq. ft404 sq. ft928 sq. ft928 sq. ft
Combined Heating Surface3463 sq. ft3549 sq. ft2909 sq. ft2926 sq. ft2926 sq. ft3064 sq. ft2841 sq. ft2859 sq. ft4347 sq. ft4389 sq. ft
Evaporative Heating Surface/Cylinder Volume302.73310.25452.09255.79206.25229.04195.96173.05198.71201.15
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation944087009570870087008700870087001406014060
Same as above plus superheater percentage944087009570870087009918991899181701317013
Same as above but substitute firebox area for grate area39640376805319648400484005494857000547208107081070
Power L1895590305829831667051572513280118201901619075
Power MT441.99419.11245.56366.67295.64711.37566.29504.03640.70631.11



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