Northern Pacific 4-8-4 "Northern" Type Locomotives

Class A (Locobase 272)

Valve motion had limited cutoff

http://www.nprr.org/Steam%20Diagrams/Forms/AllItems.aspx (7 Feb 2004) has locomotive diagrams from 1949 that supply the data.

Class A-1 (Locobase 930)

This engine demonstrated Timken's roller bearings while bearing the number 1111. (Its nickname was "The Four Aces.") Alexander (American Locomotives, 1950, p. 178) describes its tour of 88,992 miles on fourteen railroads including turns on elite passenger varnish such as the New Haven's Merchants Limited and the C&O's Sportsman. "On the Pennsylvania it handled twelve passenger cars up the Allegheny mountain grade without a helper and even saved three minutes on the standard schedule."

The NP's number for this engine was 2626. Ironically, Drury (1993), the Northern Pacific wasn't particularly persuaded by the tests because the 1111's firebox wasn't designed to burn the railroad's low-grade coal. It stayed on the NP largely because it had suffered crown sheet damage while on the railroad (the last of the 14 to trial it) and Timken didn't want it back. After repairs, the NP found 1111/2626 "durable and inexpensive to operate."

Class A-2 (Locobase 273)

Similar to the earlier Alco-built 4-8-4s with the important addition of roller bearings on the axles. The prototype was given the number 1111 and known as the "4 Aces." She was later taken into NP service as the 2626. The A-2 and A-3 series were ordered from Baldwin in 1934 (2650-2659; introduced disc driving wheels) and 1938 (2660-2667). See A-5 for later engines in the class.

Class A-3 (Locobase 932)

Virtually identical to the A-2s except for slightly larger flues and a few more tubes.

Class A-4 (Locobase 933)

This octet continued the basic Northern Pacific Northern line with a slight adjustment in heating surface area due to an increase in the number of both tubes and flues and a further enlargement of the flue diameter. Firebox heating surface, which is not shown on the 1949 diagram from which the data are taken, included 99.5 sq ft in 6 circulators.

Like the others, this set had Timken roller bearings. Unlike the earlier engines, though, the A-4s (and A-5s) had vestibule cabs that offered more protection against Northern Tier winters.

Class A-5 (Locobase 274)

Firebox heating surface included 99.7 sq ft in circulators (6) and arch tubes. Heavier engines with larger cylinders and higher drivers. The low-calorie "Rosebud" coal must have streamed through the stoker at a prodigious rate, considering that the grate demand factor is nearly as high as other engines burning higher-grade coal. These engines had a very high adhesive weight. These were booked to run 999 miles without an engine change, a record for a coal-burning locomotive.

Specifications
ClassAA-1A-2A-3A-4A-5
Locobase ID272930273932933274
RailroadNorthern Pacific (NP)Northern Pacific (NP)Northern Pacific (NP)Northern Pacific (NP)Northern Pacific (NP)Northern Pacific (NP)
Whyte4-8-44-8-44-8-44-8-44-8-44-8-4
Road Numbers2601-261226262650-26592660-26672670-26772680-2689
GaugeStdStdStdStdStdStd
BuilderAlco-SchenectadyAlcoBaldwinBaldwinBaldwinBaldwin
Year192619301934193819411943
Valve GearWalschaertWalschaertWalschaertWalschaertWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase20.25'19.25'20.66'20.66'20.67'20.66'
Engine Wheelbase47.17'45.83'48.42'48.58'45.58'48.58'
Ratio of driving wheelbase to overall engine wheebase 0.43 0.42 0.43 0.43 0.45 0.43
Overall Wheelbase (engine & tender)90'97.50'
Axle Loading (Maximum Weight per Axle)63000 lbs73800 lbs74000 lbs
Weight on Drivers251000 lbs244900 lbs294000 lbs294000 lbs294000 lbs295000 lbs
Engine Weight418000 lbs399200 lbs489400 lbs491800 lbs502500 lbs508500 lbs
Tender Light Weight313000 lbs301000 lbs387600 lbs386050 lbs443300 lbs443500 lbs
Total Engine and Tender Weight731000 lbs700200 lbs877000 lbs877850 lbs945800 lbs952000 lbs
Tender Water Capacity15000 gals14550 gals20000 gals25000 gals25000 gals
Tender Fuel Capacity (oil/coal)24 tons21 tons tons27 tons27 tons27 tons
Minimum weight per yard of rail on which locomotive could run104.58 lb rail102.04 lb rail122.50 lb rail122.50 lb rail122.50 lb rail122.92 lb rail
Geometry Relating to Tractive Effort
Driver Diameter73"73"77"77"77"77"
Boiler Pressure210 psi250 psi250 psi260 psi260 psi260 psi
Cylinders (dia x stroke)28" x 30"27" x 30"28" x 31"28" x 31"28" x 31"28" x 31"
Tractive Effort57511 lbs63663 lbs67073 lbs69756 lbs69756 lbs69756 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.36 3.85 4.38 4.21 4.21 4.23
Heating Ability
Firebox Area485 sq. ft490 sq. ft589.70 sq. ft589.70 sq. ft
Grate Area115 sq. ft88.30 sq. ft115 sq. ft115 sq. ft115 sq. ft115 sq. ft
Evaporative Heating Surface488450614964470346734672
Superheating Surface199221572035209519301930
Combined Heating Surface687672186999679866036602
Evaporative Heating Surface/Cylinder Volume228.43254.57224.69212.87211.52211.47
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation241502207528750299002990029900
Same as above plus superheater percentage31146.3428671.8137109.2339114.5538639.5138640.84
Same as above but substitute firebox area for grate area131356.2800166661.99198136.70198143.49
Power L130158.880039279.4937744.2937742.78
Power MT1059.58001178.181132.131128.25

Reference

Credits

Introduction and specifications provided by Steve Llanso of Sweat House Media.