The Atlantics that the MP bought were all built to the same basic design and delivered by the same builder. 5501-5510 came in 1904, 5511-5516 in the same year, and the balance - 5516-5540 in 1907. Most were delivered with Stephenson gear, although some of the last batch arrived fitted with Walschaerts gear operating outboard piston valves.
All were superheated in the late 'teens to the same specifications; see Locobase 7094.
A little more than a decade after the Atlantics entered service on the Missouri Pacific (Locobase 7093), the railroad decided to superheat virtually its entire Atlantic holding. It was a pretty straightforward substitution of flues for tubes and little else was changed except the valve gear. About half eventually used Walschaert gear, the other half Baker.
By 1919, only four of the 40 remained to be converted and these were completed by 1924.
A 1926 accounting shows that 38 of the engines burned coal, 2 had been converted to oil-burning. By 1929, twelve were converted to oil burning. Their tenders carried 8,000 US gallons (30,280 litres) of water and 4,250 gallons (16,087 litres) of oil fuel and weighed 148,000 lb (67,132 kg) loaded.
All of these engines and one of the coal burners were fitted with boosters that generated 9,700 lb (4,400 kg) of starting tractive effort. (Two--5513 and 5538-- later rolled on 73" drivers and used 11,020 lb (4,999 kg) boosters. The boosted locomotives weighed 212,000 lb (96,162 kg) in service.
Sixteen 4-4-2s remained on the roster in 1947, but seven were discarded in the next year, and all were gone by 1951.
Still later, the MP added 52 sq ft (4.85 sq m) of thermic syphons to the firebox heating surface area.
|Specifications by Steve Llanso of Sweat House Media|
|Class||A-79||A-79 - superheated|
|Railroad||Missouri Pacific (MP)||Missouri Pacific (MP)|
|Number in Class||10||40|
|Valve Gear||Stephenson||Baker or Walschaert|
|Locomotive Length and Weight|
|Ratio of driving wheelbase to overall engine wheebase||0.25||0.27|
|Overall Wheelbase (engine & tender)||55.71'||59.71'|
|Axle Loading (Maximum Weight per Axle)|
|Weight on Drivers||117000 lbs||119800 lbs|
|Engine Weight||194000 lbs||198600 lbs|
|Tender Light Weight||124000 lbs||124000 lbs|
|Total Engine and Tender Weight||318000 lbs||322600 lbs|
|Tender Water Capacity||9000 gals||9000 gals|
|Tender Fuel Capacity (oil/coal)||14 tons||14 tons|
|Minimum weight of rail (calculated)||98 lb/yard||100 lb/yard|
|Geometry Relating to Tractive Effort|
|Boiler Pressure||200 psi||200 psi|
|Cylinders (dia x stroke)||21" x 26"||21" x 26"|
|Tractive Effort||24674 lbs||24674 lbs|
|Factor of Adhesion (Weight on Drivers/Tractive Effort)||4.74||4.86|
|Firebox Area||187 sq. ft||238 sq. ft|
|Grate Area||44.80 sq. ft||44.90 sq. ft|
|Evaporative Heating Surface||3199 sq. ft||2548 sq. ft|
|Superheating Surface||504 sq. ft|
|Combined Heating Surface||3199 sq. ft||3052 sq. ft|
|Evaporative Heating Surface/Cylinder Volume||306.92||244.46|
|Computations Relating to Power Output (More Information)|
|Robert LeMassena's Power Computation||8960||8980|
|Same as above plus superheater percentage||8960||10507|
|Same as above but substitute firebox area for grate area||37400||55692|