Oregon-Washington RR & Navigation / San Pedro, Los Angeles & Salt Lake / Union Pacific 4-4-2 "Atlantic" Locomotives of the USA

Class Details by Steve Llanso of Sweat House Media

Class A-2 (Locobase 8876)

These were Harriman Common Standard engines; see the description of the basic design at Locobase 5340. See also data from"Report of Committe on Power-Chicago, Rock Island & Pacific Railway-Descriptions of Standard Types of Locomotives," American Engineer and Railroad Journal, Volume 79 ( March 1905), pp. 84-86. Works numbers were 23289-90, 23298-99, 23333-34, 23349-50, 23358, 23368 in December 1903 and 27383-27387, 27404, 27423-27426 in February 1906.

Locobase 4406 shows the locomotives delivered to the Oregon Short Line and the Oregon-Washington Railroad & Navigation Company subsidiaries.

The present examples have an entry to themselves because of their original road numbers. Clearly, marking a set of express passenger engines 1-20 suggests great expectations. Baldwin supplied the first group in December 1903 (to be followed by the OSL Atlantics) and picked up the work 2 years later in February 1906.

Like the other HCS Atlantics, these A-2s failed to meet those expectations, proving both slippery and underweight. They were withdrawn in the 1920s.

Class A-2/A-4 - OSL & OWR&N (Locobase 4406)

Like the A-3s of the Southern Pacific, these were Harriman Common Standard engines; see the description of the basic design at Locobase 5340. See also DeGolyer, Volume 37, p. 23. (Thanks to Chris Hohl for his 26 October 2016 email pointing out the original boiler pressure.) Built by Alco's Brooks works in 1908 (works number 45035-45038 in March 1908) and Baldwin (works numbers 23561, 23572, 23589-23590, 23615, 23624-23645 in January 1904, 23675 in February), 36068-36076, 36113-36118 in February 1911) .

The 1904 and 1908 batches went to Oregon Short Line (3400-3411) while the 1911 Baldwins went to Oregon-Washington River & Navigation as their 88-102. Like other Harrimans, these Atlantics had 12" (305 mm)-diameter piston valves. Their tenders were the cylindrical Vanderbilt design.

The Harriman Atlantics weren't entirely satisfactory, often being double-headed because of their slipperiness. Most OSLs were retired in the 1920s while the ex-OWR&N engines retired in 1928 (3506-3508 in January, 3509 in May, 3500 in June), 1929 (3512, 3514 in August), and the rest in December 1933.

Class A-3 (Locobase 5381)

Data confirmed by July 1908 table in American Engineer and Railroad Journal. See also "Atlantic Type Balanced Compound", Railway Master Mechanic, Vol XXX, #7 (July 1906), p. 336. Works numbers were 28336 in June 1906; 28616, 28625, 28639, 28655-28657, 28679-80 in July; and 28689, 28740-28743, 28929 in August.

These were the Vauclain compound version of the Harriman Common Standard engines. The design entered production 4 months after the last simple-expansion A-2s had left Baldwin's factory floor (see Locobase 8876).

An unusual component of the design were the slotted main rods coming from the inside LP cylinders and embracing the leading axle as they drove the rear axle. Like the simple Atlantics, they proved too slippery to last long on the Union Pacific. Moreover, their LP cylinders were out of proportion to the HP cylinders, yielding a ratio too high for the LP cans to be satisfactory in sharing the power load.

They were retired in 1921 and 1923 without being simpled or superheated.

Class A-81 - superheated (Locobase 7825)

These Harriman Common Standard engines (see Locobase 4406) were mostly scrapped in the 1920s. A few received a bit of a makeover that included a superheater and raising the boiler pressure to 200 psi. If they were slippery before, Locobase would suppose that increasing the tractive effort would worsen the condition. But the 4.55 factor of adhesion suggests otherwise.

By 1933, all of the OWRR&N Atlantics were out of service.

Class CT 70 / A-1 (Locobase 7260)

Data from SPLA&SL Locomotive Diagram book (the Salt Lake Route) supplied in May 2005 by Allen Stanley from his extensive Raildata collection.

This quartet of Atlantics had relatively small drivers, which suited the rail line over which they operated. Still, the design wasn't very satisfactory -- perhaps the small firebox limited steam-making -- and the class was retired in 1921.

See http://www.wemweb.com/arduous-road/build_railroad.html (accessed 5 Dec 2005) for details on constructing this railroad. The SP, LA & SL began building its line from Salt Lake City to Los Angeles via Las Vegas in 1901. In 1902, the UP acquired half of the stock from Utah Senator Williams Andrew Clark. Having shortened its name to the Los Angeles & Salt Lake (LASL) in 1916, Senator Clark sold the rest of its stock to the UP in 1921.

The LASL initials appeared on many UP-owned locomotives and rail cars for decades after.

Specifications by Steve Llanso of Sweat House Media
ClassA-2A-2/A-4 - OSL & OWR&NA-3A-81 - superheatedCT 70 / A-1
Locobase ID8876 4406 5381 7825 7260
RailroadUnion Pacific (UP)Union Pacific (UP)Union Pacific (UP)Oregon-Washington RR & Navigation (UP)San Pedro, Los Angeles & Salt Lake (UP)
Number in Class20271544
Road Numbers1-20 / 3300-3319850-861, 88-102/3400-3411, 3500-351421-35 / 3320-33343503, 3505, 3510, 35133100-3103 / 3376-3379
Number Built2027154
BuilderBurnham, Williams & CoseveralBurnham, Williams & CoshopsAlco
Valve GearStephensonStephensonWalschaertStephensonWalschaert
Locomotive Length and Weight
Driver Wheelbase7'7'7'7' 7.50'
Engine Wheelbase27.58'27.58'27.83'27.58'26.17'
Ratio of driving wheelbase to overall engine wheebase 0.25 0.25 0.25 0.25 0.29
Overall Wheelbase (engine & tender)58.17'57.31'58.72'59.46'59.08'
Axle Loading (Maximum Weight per Axle)53500 lbs56000 lbs53450 lbs
Weight on Drivers107000 lbs105000 lbs110000 lbs106900 lbs107000 lbs
Engine Weight197000 lbs196000 lbs209000 lbs199726 lbs167000 lbs
Tender Light Weight133050 lbs138070 lbs133050 lbs147776 lbs106635 lbs
Total Engine and Tender Weight330050 lbs334070 lbs342050 lbs347502 lbs273635 lbs
Tender Water Capacity7000 gals7000 gals7000 gals5500 gals
Tender Fuel Capacity (oil/coal)14 tons2940 gals14 tons tons1748 gals
Minimum weight of rail (calculated)89 lb/yard88 lb/yard92 lb/yard89 lb/yard89 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter81"81"81"81"70"
Boiler Pressure190 psi200 psi200 psi200 psi200 psi
High Pressure Cylinders (dia x stroke)20" x 28"20" x 28"16" x 28"20" x 28"19" x 26"
Low Pressure Cylinders (dia x stroke)27" x 28" (2)
Tractive Effort22331 lbs23506 lbs22268 lbs23506 lbs22795 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.79 4.47 4.94 4.55 4.69
Heating Ability
Firebox Area180 sq. ft174 sq. ft180 sq. ft174 sq. ft135 sq. ft
Grate Area49.50 sq. ft49.50 sq. ft49.50 sq. ft49.50 sq. ft42.20 sq. ft
Evaporative Heating Surface2655 sq. ft2649 sq. ft2655 sq. ft2196 sq. ft2852 sq. ft
Superheating Surface328 sq. ft
Combined Heating Surface2655 sq. ft2649 sq. ft2655 sq. ft2524 sq. ft2852 sq. ft
Evaporative Heating Surface/Cylinder Volume260.78260.19407.47215.69334.27
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation94059900990099008440
Same as above plus superheater percentage940599009900111878440
Same as above but substitute firebox area for grate area3420034800360003932427000
Power L1895693325173159609646
Power MT369.06391.88207.35658.29397.49


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