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.
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.
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.
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.
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.
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.
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.
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.
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.
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|
|Class||6000||6001||P-69||P-69 - superheated||P-73||P-73||P-73 / 1151||P-73 / 6401||P-73 / 6420||P-73 / 6601|
|Railroad||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)||Missouri Pacific (MP)|
|Road Numbers||6000||6001||1115-1123, 1616-1627||1115-1123, 1616-1627||6440-6444||6440-6444||1151-1161||6401-6419||6420-6439 (+ rebuilds)||6601-6629|
|Valve Gear||Walschaert||poppet||Stephenson||Baker||various||various||Baker||Walschaert||Walschaert||Baker or Walschaert|
|Locomotive Length and Weight|
|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 Drivers||191000 lbs||187785 lbs||118000 lbs||124000 lbs||166500 lbs||176850 lbs||190520 lbs||156000 lbs||160500 lbs||197700 lbs|
|Engine Weight||311000 lbs||314755 lbs||185000 lbs||193000 lbs||267500 lbs||282300 lbs||294000 lbs||246000 lbs||256000 lbs||312810 lbs|
|Tender Light Weight||148400 lbs||148400 lbs||168200 lbs||256400 lbs||156500 lbs||156500 lbs||256400 lbs|
|Total Engine and Tender Weight||333400 lbs||341400 lbs||435700 lbs||550400 lbs||402500 lbs||412500 lbs||569210 lbs|
|Tender Water Capacity||12000 gals||18000 gals||7000 gals||7000 gals||8000 gals||12000 gals||8000 gals||8000 gals||12000 gals|
|Tender Fuel Capacity (oil/coal)||16 tons||5650 gals||14 tons||14 tons||14 tons||tons||5000 gals||14 tons||14 tons||6610 gals|
|Minimum weight of rail (calculated) on which locomotive could run||106 lb/yard||104 lb/yard||66 lb/yard||69 lb/yard||93 lb/yard||98 lb/yard||106 lb/yard||87 lb/yard||89 lb/yard||110 lb/yard|
|Geometry Relating to Tractive Effort|
|Boiler Pressure||190 psi||200 psi||200 psi||200 psi||190 psi||200 psi||188.50 psi||200 psi||180 psi||200 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 Effort||47040 lbs||47535 lbs||25623 lbs||28250 lbs||38884 lbs||40930 lbs||44802 lbs||32583 lbs||38973 lbs||47535 lbs|
|Factor of Adhesion (Weight on Drivers/Tractive Effort)||4.06||3.95||4.61||4.39||4.28||4.32||4.25||4.79||4.12||4.16|
|Firebox Area||254 sq. ft||264 sq. ft||175 sq. ft||221 sq. ft||233 sq. ft||271 sq. ft||266 sq. ft||209.70 sq. ft||209.70 sq. ft||274 sq. ft|
|Grate Area||66.70 sq. ft||67.20 sq. ft||42.40 sq. ft||42.40 sq. ft||49.50 sq. ft||49.50 sq. ft||67.80 sq. ft||50 sq. ft||49.50 sq. ft||67.80 sq. ft|
|Evaporative Heating Surface||3624 sq. ft||4028 sq. ft||2954 sq. ft||2322 sq. ft||3283 sq. ft||3511 sq. ft||3719 sq. ft||4108 sq. ft||3450 sq. ft||3904 sq. ft|
|Superheating Surface||1019 sq. ft||1354 sq. ft||430 sq. ft||778 sq. ft||778 sq. ft||1054 sq. ft||722 sq. ft||980 sq. ft|
|Combined Heating Surface||4643 sq. ft||5382 sq. ft||2954 sq. ft||2752 sq. ft||4061 sq. ft||4289 sq. ft||4773 sq. ft||4108 sq. ft||4172 sq. ft||4884 sq. ft|
|Evaporative Heating Surface/Cylinder Volume||187.50||217.08||312.46||222.78||205.48||219.75||200.43||341.71||215.93||210.40|
|Computations Relating to Power Output (More Information)|
|Robert LeMassena's Power Computation||12673||13440||8480||8480||9405||9900||12780||10000||8910||13560|
|Same as above plus superheater percentage||15461||16800||8480||9837||11192||11682||15592||10000||10425||16272|
|Same as above but substitute firebox area for grate area||58877||66000||35000||51272||52681||63956||61172||41940||44163||65760|