Missouri Pacific 4-6-2 "Pacific" Type Locomotives

Class Details by Steve Llanso

Class 6000 (Locobase 152)

Data from tables in 1930 Locomotive Cyclopedia. (Thanks to Chris Hohl for the valve gear ID and for pointing out the mixed valve-gear setup, which is described in Alfred Bruce, The Steam Locomotive in America (New York: Bonanza Books, 1952), pp. 201-201, 210.) .)

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.

Firebox had combustion chamber. One of three three-cylinder locomotive designs built by Alco in 1925. (The others were Rock Island's P-46 class-Locobase 142-and L&N's #295.) The MP was the heaviest and had a slightly higher superheat/CHS ratio. It also had by far the biggest tender.

As noted in the entry on MoPac's three-cylinder 2-8-2 (#22), trials showed low fuel consumption and impressive tractive effort. Bruce's diagram shows that like the other Alco three-cylinder locomotives, all three cylinders were line abreast and roughly equally spaced. But the two right-hand piston valves were closely spaced over the right-hand cylinder and linked together by a solid arm that pivoted around its center, thus actuating first the central valve, then the outside right valve.

In service, however, the maintenance demands of that inside third cylinder outweighed any performance benefit. For a long time, 6000 sat idle, then was rebuilt as essentially a new 2-cylinder engine; see Locobase 9394.

Class 6001 (Locobase 9394)

Data from MP7 - 1956 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

Locobase 152 shows the original locomotive 6000 as it was delivered in 1925 with its 3-cylinder layout. As noted, the 3-cylinder arrangement's additional power never quite justified the cost. So after letting the orphan sit idle for several years, the MP completely rebuilt it.

Conversion first as a poppet-valves testbed, then with roller bearings, removal of the third cylinder, oil firing, and Elesco feedwater heater. When completed, the new/old engine had 2 27 x 28" cylinders, a boiler pressed to 200 psi and possessing 4,028 sq ft of heating surface, thermic syphons in the firebox..

Although tractive effort remained about the same, the overhaul transformed the now-renumbered 6001 and she proved a powerful and reliable engine until her 1952 retirement. Her only weak spot was the "poor man's feedwater heater," the Elesco ES. This proved a problematical device that was very sensitive to bad water. When on her mettle, however, the 6001 hit 90-95 mph regularly.

Even so, the MP saw no particular need to retrofit any of its other Pacifics in a similar way.

See WM Adams (Trains, November 1978) for a full account of the modified 6001 "Madame Queen" and the prodigies of speed of which she was capable.

Class P-69 (Locobase 151)

Among the first Pacifics, these had the then-common inside valve motion and trailing-truck bearings. Firebox heating surface included 22 sq ft of arch tubes. Data from AERJ July 1903, supplemented by data from MP 1924 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

Two number sequences, the first for Missouri Pacific, the other for Iron Mountain. The 1905 renumbering put in the 6501-6521 sequence. All were rebuilt with Baker valve gear (except one with Walschaerts) driving outside piston valves and the steam was superheated. The last left service in 1953.

Class P-69 - superheated (Locobase 9396)

Data from MP 1924 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

Locobase 151 shows these pioneering Pacifics in their original saturated-steam configuration. All were rebuilt with Baker valve gear (except one with Walschaerts) driving outside 11" piston valves and the steam was superheated. In the process, the cylinder diameter grew by an inch and, as usually happened in these early conversions, the boiler lost some of its total evaporative heating surface. Later retrofits added 10 sq ft of arch tubes and 36 sq ft of thermic syphons.

The last left service in 1953.

Class P-73 (Locobase 14958)

Data from MP 7 - 1956 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection. (My thanks to Chris Hohl for his 21 February 2013 inquiry that led to several new entries and updates of several more.)

The quintet of express passenger Pacifics bought by the MP in 1921 from Schenectady (Locobase 14957) were continuations of a larger class originally built in 1910-1912. This later batch was fitted with Harter circulating plates (see the earlier entry for full description and bibliographic references).

At a later time, the MP reworked the boiler and firebox considerably. Locobase can't be sure, but he believes that the Harter plates were removed, but the tube count increased by 16. Two thermic syphons replaced the arch tubes in the firebox and contributed 65 sq ft (6 sq m) to direct heating surface. They were fitted with Timken roller bearings, a BK stoker, and power reverse gear.

Class P-73 (Locobase 14957)

Data from "New Locomotives for the Missouri Pacific", Railway Mechanical Engineer, Vol 95, No 10 (October 1921), pp. 609-613; and F G Lister, "Locomotive Boiler Efficiencey by Proper Circulation of Water", The Boiler Maker, Vol 22, No 9 (September 1922), pp. 256-257. (My thanks to Chris Hohl for his 21 February 2013 inquiry that led to several new entries and updates of several more.) Built at Schenectady in April 1921.

Like the other locomotives ordered by the MoPac from Alco in this year, the Pacifics were fitted with Harter Circulating Plates. Locobase 14956 has a full description of this device. (Briefly, a solid plate laid horizontally among the superheater flues and pierced for 2" diameter steam risers sought to encourage circulation from bottom to top.) Arch tubes added 26 sq ft (2.4 sq m) to direct heating surface area and 14" (356 mm) piston valves supplied steam to the cylinders.

These were later rebuilt by the MP with a new boiler; see Locobase 14958.

Class P-73 / 1151 (Locobase 153)

Data from tables in 1930 Locomotive Cyclopedia, supplemented by MP 8 - 1936 locomotive diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

Firebox had combustion chamber. Ran in Texas for the International-Great Northern (1151-1155) and St. Louis, Brownsville & Mexico (1156-1161). The IGNs had Baker gear, Worthington SA feedwater heaters, the others Worthington BLs.

Class P-73 / 6401 (Locobase 9395)

Data from MP 1924 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection. (My thanks to Chris Hohl for his 21 February 2013 inquiry that led to several new entries and updates of several more.)

The first half of a large batch of 73" driver Pacifics were delivered with saturated boilers of a relatively small size matched to a modest cylinder volume.

Class P-73 / 6420 (Locobase 1373)

Data from MP 1924 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection. (My thanks to Chris Hohl for his 21 February 2013 inquiry that led to several new entries and updates of several more.)

The 6420-6439 were follow-ons to the Brooks engines, but much bigger and fitted with square cylinders (bore equalled stroke) that increased cylinder volume by a third. The first 19 were delivered as saturated-steam engines; those are shown in Locobase 9395. By 1912, the class was being delivered with superheaters and the first group was soon converted. In the process, the cylinder volume grew considerably and total evaporative heating surface actually increased.

1921 saw the delivery of 5 more (6440-6444) fitted with Harter circulating plates (Locobase 14958).

In later years, the firebox was modified with 65 sq ft of thermic syphons, which increased the total firebox heating surface to 271 sq ft. The class also received 73" drivers and some had roller bearings and Elesco feedwater heaters.

Class P-73 / 6601 (Locobase 9397)

Data from MP 7 - 1956 locomotive diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

Firebox had combustion chamber. Drury (1993) notes that the first 10 were delivered as 6445-6454; they were renumbered in 1934. The design was an interesting combination of the USRA's Heavy Pacific boiler and the Light Pacific's 73" drivers. Cast trailing trucks were standard. 6614-6619 were oil-burners to provide clean power for the MP's Sunshine Special.

As often happens in such classes, modifications over time ensured variety. By the 1940s, Drury tells us, "...no two engines in the class had the same combination of disk main drivers, roller bearings, pilots, and tender."

The clas was retired in 1949-1954.


Specifications by Steve Llanso
Class60006001P-69P-69 - superheatedP-73P-73P-73 / 1151P-73 / 6401P-73 / 6420P-73 / 6601
Locobase ID152 9394 151 9396 14958 14957 153 9395 1373 9397
RailroadMissouri Pacific (MP)Missouri Pacific (MP)Missouri Pacific (MP)Missouri Pacific (MP)Missouri Pacific (MP)Missouri Pacific (MP)Missouri Pacific (MP)Missouri Pacific (MP)Missouri Pacific (MP)Missouri Pacific (MP)
CountryUSAUSAUSAUSAUSAUSAUSAUSAUSAUSA
Whyte4-6-24-6-24-6-24-6-24-6-24-6-24-6-24-6-24-6-24-6-2
Road Numbers600060011115-1123, 1616-16271115-1123, 1616-16276440-64446440-64441151-11616401-64196420-6439 (+ rebuilds)6601-6629
GaugeStdStdStdStdStdStdStdStdStdStd
BuilderAlcoMPBrooksMPAlco-SchenectadyAlco-SchenectadyAlcoAlcoAlcoAlco
Year192519421902191619211926191019121924
Valve GearWalschaertpoppetStephensonBakervariousvariousBakerWalschaertWalschaertBaker or Walschaert
Locomotive Length and Weight
Driver Wheelbase14.33'14.33'12.33'12.33'13'13'13'13'13'13'
Engine Wheelbase36.58'36.58'31.67'31.67'33.58'33.58'35.25'33.25'33.25'35.25'
Ratio of driving wheelbase to overall engine wheebase 0.39 0.39 0.39 0.39 0.39 0.39 0.37 0.39 0.39 0.37
Overall Wheelbase (engine & tender)76.17'76.17'55.17'55.17'67.02'67.02'74.83'65.29'65.29'74.83'
Axle Loading (Maximum Weight per Axle)63800 lbs
Weight on Drivers191000 lbs187785 lbs118000 lbs124000 lbs176850 lbs166500 lbs190520 lbs156000 lbs160500 lbs197700 lbs
Engine Weight311000 lbs314755 lbs185000 lbs193000 lbs282300 lbs267500 lbs294000 lbs246000 lbs256000 lbs312810 lbs
Tender Light Weight148400 lbs148400 lbs168200 lbs256400 lbs156500 lbs156500 lbs256400 lbs
Total Engine and Tender Weight333400 lbs341400 lbs435700 lbs550400 lbs402500 lbs412500 lbs569210 lbs
Tender Water Capacity12000 gals18000 gals7000 gals7000 gals8000 gals12000 gals8000 gals8000 gals12000 gals
Tender Fuel Capacity (oil/coal)16 tons5650 gals14 tons14 tons tons14 tons5000 gals14 tons14 tons6610 gals
Minimum weight of rail (calculated) on which locomotive could run106 lb/yard104 lb/yard66 lb/yard69 lb/yard98 lb/yard93 lb/yard106 lb/yard87 lb/yard89 lb/yard110 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter73"73"69"69"73"73"73"69"69"73"
Boiler Pressure190 psi200 psi200 psi200 psi200 psi190 psi188.50 psi200 psi180 psi200 psi
Cylinders (dia x stroke)22.5" x 28" (3)27" x 28"20" x 26"21" x 26"26" x 26"26" x 26"27" x 28"23" x 25"26" x 26"27" x 28"
Tractive Effort47040 lbs47535 lbs25623 lbs28250 lbs40930 lbs38884 lbs44802 lbs32583 lbs38973 lbs47535 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.06 3.95 4.61 4.39 4.32 4.28 4.25 4.79 4.12 4.16
Heating Ability
Firebox Area254 sq. ft264 sq. ft175 sq. ft221 sq. ft271 sq. ft233 sq. ft266 sq. ft209.70 sq. ft209.70 sq. ft274 sq. ft
Grate Area66.70 sq. ft67.20 sq. ft42.40 sq. ft42.40 sq. ft49.50 sq. ft49.50 sq. ft67.80 sq. ft50 sq. ft49.50 sq. ft67.80 sq. ft
Evaporative Heating Surface3624 sq. ft4028 sq. ft2954 sq. ft2322 sq. ft3511 sq. ft3283 sq. ft3719 sq. ft4108 sq. ft3450 sq. ft3904 sq. ft
Superheating Surface1019 sq. ft1354 sq. ft430 sq. ft778 sq. ft778 sq. ft1054 sq. ft722 sq. ft980 sq. ft
Combined Heating Surface4643 sq. ft5382 sq. ft2954 sq. ft2752 sq. ft4289 sq. ft4061 sq. ft4773 sq. ft4108 sq. ft4172 sq. ft4884 sq. ft
Evaporative Heating Surface/Cylinder Volume187.50217.08312.46222.78219.75205.48200.43341.71215.93210.40
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation126731344084808480990094051278010000891013560
Same as above plus superheater percentage154611680084809837116821119215592100001042516272
Same as above but substitute firebox area for grate area58877660003500051272639565268161172419404416365760
Power L1168222299493151610218075165671796598651424718483
Power MT582.50809.86522.10858.84675.97658.09623.65418.24587.09618.33

Reference

Credits

Introduction and roster provided by Richard Duley. Class details and specifications provided by Steve Llanso of Sweat House Media.