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Missouri Pacific class P-69
United States | 1902 | 21 produced
Railway ans Locomotive Engineering, November 1904

While the first 4-6-2 locomotives still had a narrow firebox and did not bring much advantage over the 4-6-0, the later, classic Pacifics were characterized by a wide firebox above the trailing axle. This allowed a sufficiently large grate area to maintain high speeds with heavy trains, as had been the case with the Atlantic-type express locomotives a few years earlier. While the Pacific was used almost exclusively as express locomotive in Europe, there were also many engines in North America with slightly smaller coupled wheels, which were primarily intended for the heaviest, more medium-speed passenger trains.

The first model of this type were the 21 Missouri Pacific locomotives, which were built by ALCO-Brooks in 1902 and formed the basis for the name “Pacific”. They were lighter than other Pacifics that were built in the following years and had a coupled wheel diameter of only 69 inches. Together with the abbreviation "P" for “Pacific”, this led to the class designation P-69.

Since the locomotives were partly built directly for the Missouri Pacific and partly for their subsidiary St. Louis, Iron Mountain and Southern Railway, they were given separate number ranges between 1115 and 1123 and between 1616 and 1623. The Stephenson valve gear was later replaced on 20 engines by a Baker valve gear and on one engine by the Walschaerts valve gear. In 1916 the conversion to superheated steam took place, in which the cylinder diameter was increased by one inch. The last examples served in this form until 1953.

Variantas builtsuperheated
General
Built19021916
ManufacturerALCOMissouri Pacific
Axle config4-6-2 (Pacific) 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Wheelbase30 ft 5 in31 ft 8 in
Fixed wheelbase12 ft 4 in
Total wheelbase55 ft 1 1/2 in55 ft 2 in
Service weight173,000 lbs193,000 lbs
Adhesive weight120,000 lbs124,000 lbs
Total weight283,000 lbs341,400 lbs
Axle load40,000 lbs41,333 lbs
Water capacity5,000 us gal7,000 us gal
Fuel capacity20,000 lbs (coal)28,000 lbs (coal)
Power
Power sourcesteam
Estimated power1,500 hp (1,119 kW)
Optimal speed37 mph34 mph
Starting effort25,623 lbf28,250 lbf
Power Plant
Driver diameter69 in
Boiler pressure200 psi
Expansion typesimple
Cylinderstwo, 20 x 26 intwo, 21 x 26 in
Boiler
Grate area42.4 sq ft
Firebox area174 sq ft221 sq ft
Tube heating area2,779 sq ft2,101 sq ft
Evaporative heating area2,953 sq ft2,322 sq ft
Superheater area430 sq ft
Total heating area2,953 sq ft2,752 sq ft
Calculated Values
steam locomotive
express
last changed: 09/2022
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