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.
Almost all (at least 36) were later superheated to the same specifications; see Locobase 7094.
At some point, the Missouri Pacific 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.
| Specifications | ||
|---|---|---|
| Class | A-79 | A-79 - superheated |
| Locobase ID | 7093 | 7094 |
| Railroad | Missouri Pacific (MP) | Missouri Pacific (MP) |
| Whyte | 4-4-2 | 4-4-2 |
| Road Numbers | 5501-5540 | 5501-5540 |
| Gauge | Std | Std |
| Builder | Alco-Brooks | Alco-Brooks |
| Year | 1904 | |
| Valve Gear | Stephenson | Baker or Walschaert |
| Locomotive Length and Weight | ||
| Driver Wheelbase | 7.50' | 7.50' |
| Engine Wheelbase | 29.67' | 29.67' |
| Ratio of driving wheelbase to overall engine wheebase | 0.25 | 0.25 |
| Overall Wheelbase (engine & tender) | 55.71' | 55.71' |
| Axle Loading (Maximum Weight per Axle) | ||
| Weight on Drivers | 117000 lbs | 119800 lbs |
| Engine Weight | 194000 lbs | 191600 lbs |
| Tender Light Weight | 124000 lbs | 124000 lbs |
| Total Engine and Tender Weight | 318000 lbs | 315600 lbs |
| Tender Water Capacity | 9000 gals | 9000 gals |
| Tender Fuel Capacity (oil/coal) | 14 tons | 14 tons |
| Minimum weight per yard of rail on which locomotive could run | 98 lb rail | 100 lb rail |
| Geometry Relating to Tractive Effort | ||
| Driver Diameter | 79" | 79" |
| 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 |
| Heating Ability | ||
| Firebox Area | 187 sq. ft | 187 sq. ft |
| Grate Area | 44.80 sq. ft | 44.80 sq. ft |
| Evaporative Heating Surface | 3199 | 2538 |
| Superheating Surface | 504 | |
| Combined Heating Surface | 3199 | 3042 |
| Evaporative Heating Surface/Cylinder Volume | 306.92 | 243.50 |
| Computations Relating to Power Output (More Information) | ||
| Robert LeMassena's Power Computation | 8960 | 8960 |
| Same as above plus superheater percentage | 8960 | 10752 |
| Same as above but substitute firebox area for grate area | 37400 | 44880 |
| Power L1 | 10445 | 20235 |
| Power MT | 393.63 | 744.75 |
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