Southern Pacific 2-8-8-2 "Chesapeake" Locomotives of the USA


Class Details by Steve Llanso of Sweat House Media

Class AC-1/AC-2/AC-3 (Locobase 9296)

Data from SP Menke All Time Steam Locomotive diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection.

Originally placed into service as Mallet Consolidations (MC), several classes of 2-8-8-2 cab-forwards were simpled and superheated, being redesignated Articulated Consolidations (but still called Mallets). The first of the updates resulted in a modest overhaul (see Locobase 9295) that clearly didn't satisfy and a new layout was adopted. The new program was undertaken at the same time later AC classes were being produced by Baldwin. Locobase doesn't know which influenced which, but both major upgrades (modifications and new-builds) included the Type E superheater and its larger surface area.

Compared to the later ACs, however, the MC conversions were smaller engines with less capacious grates and fireboxes. The tubes were longer than those of the later AC class engines, as was the combustion chamber.

17 MC-1 (Locobase 339) & MC-2s, 11 MC-4s (Locobase 3358) , and all 20 MC-6s (Locobase 8724) were rebuilt, including the 4000-4001, which were conventional-cab locomotives and did not operate in the Sierras, and the 4041, which was the first superheated and had different data; see Locobase 9296


Class AC-3a (Locobase 9295)

Data from SP Menke All Time Steam Locomotive diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection.

Locobase 9296 describes the general course of simpling and superheating that was applied to the several Mallet Consolidation classes in 1928-1927. These all had Type E superheaters and the entire installation represented a substantial makeover.

One year earlier, however, the Espee had begun the project with the less-ambitious update shown here that used a Type A superheater, shorter tubes, and no combustion chamber. It seems clear that the railroad concluded that this was an insufficiently powerful update and turned to a much different layout.


Class MC-1 (Locobase 329)

Data from SP Menke All Time Steam Locomotive diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection. See also DeGolyer, Volume 32, pp. 85+ and "Locomotives Headed the Other Way," Railway Journal, Vol 16, No 2 (February 1910), pp. 18-19. Works numbers 33340-33341 in April 1909

Conventional Mallet compound predecessors of later "cab-forward" Espee articulateds. As US builders and railroads began adopting superheaters, several variations appeared before the Schmidt smokebox superheater became the preferred installation. Among the early designs was a Baldwin set up that placed a relatively large feedwater heater (1,221 sq ft/113.45 sq m) between two sections of boiler. Its reheater design was an apparatus that lined the inside of the smokebox. Steam exhausted from the HP cylinders was circulated through the 655 sq ft (60.85 sq m)of the reheater before being directed to the LP cylinders.

The design was modestly successful as a heavy freight pusher, but its conventional layout allowed nearly lethal exhaust to swirl into the cab as the engine traveled through the SP's many tunnels and snowsheds. To combat this oppressive condition, the two were later rebuilt as simple articulateds with the cab-forward design.


Class MC-2/MC-4 (Locobase 3558)

Data from SP Menke All Time Steam Locomotive diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection. See also DeGolyer, Volume

33, p. 306. MC-2s followed the MC-1s in production seven months later in November 1909 as works numbers were 34019, 34043-34044, 34046-34047, 34063-34067, 34093-34097.

MC-4s (4017-4028) followed in April 1911 (works numbers 36490-36493) and May (36524-36527, 36614-36616, 36634), and MC-6 (4029-4043) were produced in October 1912 as works works numbers 38523-38534 and 38711-38713 in December 1912.

Like the MC-1, this class had a small (655 sq ft/60.85 sq m) reheater for the LP cylinders, but a larger "pre-heater", which Baldwin called a feed water heater, that used the same tube layout as the longer firetubes but heated water with exhaust gas. Each of these tubes was 63" (1,600 mm) long and together comprised 1,221 sq ft (113.43 sq m) . The combustion chamber lay between the firebox and the feed water heater. The four 15" (381 mm) piston valves had removable bushings.

Later the MCs (Mallet Consolidations) became AC (Articulated Consolidations) when they were simpled in the 1920s. See Locobase 9626.


Class MC-6 (Locobase 8724)

Data from SP Menke All Time Steam Locomotive diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection. See also DeGolyer, Volume 46, pp.111+. Works numbers were 38523-38534 in October 1912, 38711-38713 in November

Locobase 329 describes the conventional-cab MC-1s, which introduced the Baldwin feedwater heater as a separate section between two sections of boiler and a Baldwin reheater (of HP exhaust steam). To overcome exhaust-fume poisoning, the builder turned the next group of engines around. As the "cab-forward" or "back-up" MC-2 & MC-4, those articulateds retained both features.

The MC-6 class also had the 1,221-sq ft (113.43 sq ft) heater (area not included in the evaporative heating surface area) that used the same tube layout as the longer firetubes but heated water with exhaust gas. The builder discarded Baldwin's reheater for a Schmidt superheater, however, which would prove to be the preferred form of reheating steam. All four cylinders received steam through 15" (381 mm) piston valves.

Later the MCs (Mallet Consolidations) became AC (Articulated Consolidations) when they were simpled in the 1920s.

Specifications by Steve Llanso of Sweat House Media
ClassAC-1/AC-2/AC-3AC-3aMC-1MC-2/MC-4MC-6
Locobase ID9296 9295 329 3558 8724
RailroadSouthern Pacific (SP)Southern Pacific (SP)Southern Pacific (SP)Southern Pacific (SP)Southern Pacific (SP)
CountryUSAUSAUSAUSAUSA
Whyte2-8-8-22-8-8-22-8-8-22-8-8-22-8-8-2
Number in Class47122715
Road Numbers4000-404540414000-40014002-40284029-4043
GaugeStdStdStdStdStd
Number Built22715
BuilderSPSPBaldwinBaldwinBaldwin
Year19281927190919091912
Valve GearWalschaertWalschaertWalschaertWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase15'15'15'15'15'
Engine Wheelbase56.59'56.58'56.58'56.59'56.59'
Ratio of driving wheelbase to overall engine wheebase 0.27 0.27 0.27 0.27 0.27
Overall Wheelbase (engine & tender)90.33'90.33'83.50'90.33'90.33'
Axle Loading (Maximum Weight per Axle)50260 lbs51200 lbs
Weight on Drivers440800 lbs440800 lbs394145 lbs398000 lbs400700 lbs
Engine Weight481200 lbs481200 lbs425900 lbs433600 lbs435800 lbs
Tender Light Weight180200 lbs179400 lbs184660 lbs
Total Engine and Tender Weight481200 lbs481200 lbs606100 lbs613000 lbs620460 lbs
Tender Water Capacity10000 gals10000 gals10800 gals10000 gals10000 gals
Tender Fuel Capacity (oil/coal)3200 gals3200 gals3420 gals3200 gals3200 gals
Minimum weight of rail (calculated)92 lb/yard92 lb/yard82 lb/yard83 lb/yard83 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter57"57"57"57"57"
Boiler Pressure210 psi210 psi200 psi200 psi200 psi
High Pressure Cylinders (dia x stroke)22" x 30"22" x 30"26" x 30"26" x 30"26" x 30"
Low Pressure Cylinders (dia x stroke)40" x 30" (2)40" x 30" (2)40" x 30" (2)
Tractive Effort90941 lbs90941 lbs85039 lbs85039 lbs85039 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.85 4.85 4.63 4.68 4.71
Heating Ability
Firebox Area362 sq. ft240 sq. ft232 sq. ft240 sq. ft240 sq. ft
Grate Area68.40 sq. ft68.40 sq. ft68.40 sq. ft68.40 sq. ft68.40 sq. ft
Evaporative Heating Surface4876 sq. ft4417 sq. ft5173 sq. ft4941 sq. ft4177 sq. ft
Superheating Surface2150 sq. ft839 sq. ft655 sq. ft839 sq. ft
Combined Heating Surface7026 sq. ft5256 sq. ft5828 sq. ft4941 sq. ft5016 sq. ft
Evaporative Heating Surface/Cylinder Volume184.71167.32280.61268.02226.58
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation1436414364136801368013680
Same as above plus superheater percentage1881716662151851368016006
Same as above but substitute firebox area for grate area9958658464515044800056160
Power L1196769952532526745629
Power MT787.26398.19238.28118.50247.76

Photos

Reference


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