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
Class	A	A-1	A-2	A-3	A-4	A-5
Locobase ID	272	930	273	932	933	274
Railroad	Northern Pacific (NP)	Northern Pacific (NP)	Northern Pacific (NP)	Northern Pacific (NP)	Northern Pacific (NP)	Northern Pacific (NP)
Whyte	4-8-4	4-8-4	4-8-4	4-8-4	4-8-4	4-8-4
Road Numbers	2601-2612	2626	2650-2659	2660-2667	2670-2677	2680-2689
Gauge	Std	Std	Std	Std	Std	Std
Builder	Alco-Schenectady	Alco	Baldwin	Baldwin	Baldwin	Baldwin
Year	1926	1930	1934	1938	1941	1943
Valve Gear	Walschaert	Walschaert	Walschaert	Walschaert	Walschaert	Walschaert
	Locomotive Length and Weight
Driver Wheelbase	20.25'	19.25'	20.66'	20.66'	20.67'	20.66'
Engine Wheelbase	47.17'	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 lbs		73800 lbs			74000 lbs
Weight on Drivers	251000 lbs	244900 lbs	294000 lbs	294000 lbs	294000 lbs	295000 lbs
Engine Weight	418000 lbs	399200 lbs	489400 lbs	491800 lbs	502500 lbs	508500 lbs
Tender Light Weight	313000 lbs	301000 lbs	387600 lbs	386050 lbs	443300 lbs	443500 lbs
Total Engine and Tender Weight	731000 lbs	700200 lbs	877000 lbs	877850 lbs	945800 lbs	952000 lbs
Tender Water Capacity	15000 gals	14550 gals		20000 gals	25000 gals	25000 gals
Tender Fuel Capacity (oil/coal)	24 tons	21 tons	tons	27 tons	27 tons	27 tons
Minimum weight per yard of rail on which locomotive could run	104.58 lb rail	102.04 lb rail	122.50 lb rail	122.50 lb rail	122.50 lb rail	122.92 lb rail
	Geometry Relating to Tractive Effort
Driver Diameter	73"	73"	77"	77"	77"	77"
Boiler Pressure	210 psi	250 psi	250 psi	260 psi	260 psi	260 psi
Cylinders (dia x stroke)	28" x 30"	27" x 30"	28" x 31"	28" x 31"	28" x 31"	28" x 31"
Tractive Effort	57511 lbs	63663 lbs	67073 lbs	69756 lbs	69756 lbs	69756 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort)	4.36	3.85	4.38	4.21	4.21	4.23
	Heating Ability
Firebox Area	485 sq. ft			490 sq. ft	589.70 sq. ft	589.70 sq. ft
Grate Area	115 sq. ft	88.30 sq. ft	115 sq. ft	115 sq. ft	115 sq. ft	115 sq. ft
Evaporative Heating Surface	4884	5061	4964	4703	4673	4672
Superheating Surface	1992	2157	2035	2095	1930	1930
Combined Heating Surface	6876	7218	6999	6798	6603	6602
Evaporative Heating Surface/Cylinder Volume	228.43	254.57	224.69	212.87	211.52	211.47
	Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation	24150	22075	28750	29900	29900	29900
Same as above plus superheater percentage	31146.34	28671.81	37109.23	39114.55	38639.51	38640.84
Same as above but substitute firebox area for grate area	131356.28	0	0	166661.99	198136.70	198143.49
Power L1	30158.88	0	0	39279.49	37744.29	37742.78
Power MT	1059.58	0	0	1178.18	1132.13	1128.25