The AERJ report noted that these engines were headed for both regular service and pusher duty on the Chicago, Milwaukee & Puget Sound Lines. Seventeen burned coal while eight more were oil burners dedicated to the Idaho Forest Reserve segment of the Milwaukee's road. Because they were produced in the face of imminent conversion to delivering superheated boilers by most builders, they had the largest evaporative heating surface area of any 2-6-6-2 produced.
The AERJ commented that the most novel feature of this design was the provision of a separate exhaust pipe from each of the low-pressure cylinders. "It has been found that with the ordinary single exhaust pipe on Mallet locomotives, wherein the passages come together in the cylinder casting before entering the flexible pipe, there is a noticeable back pressure created by the exhaust from one cylinder backing up into the exhaust cavity of the other. Therefore in this case the exhaust is carried through entirely separate passages, and includes even separate tips."
Doubtless familiar with the resistance to needless complexity inherent in American master mechanics, the AERJ added: "While this increases the number of flexible joints, since there are two flexible exhaust pipes from the low pressure cylinders, it is believed that the reduction in back pressure will offset this disadvantage"
At this point in its compounding history, Alco typically used the Mellin compounding system. AERJ reminded its readers: "There is a separate exhaust lead from the intercepting valve chamber in the high pressure cylinder to the front end, so that when working simple the exhaust from the high pressure cylinder does not enter the receiver pipe." It too was kept separate from the other two exhausts.
For some reason, even though the N-2 (Locobase 15053) was delivered as a superheated locomotive, only the N-1s were used as the basis for the rebuilding program that created the simple N-3 (Locobase 298).
Directly derived from the N1 class shown in Locobase 15054, the N2s were superheated from the start. This large boiler had a generous combustion chamber that added some amount of heating surface to the direct heating surface area.
9601-9602 and 9606 were renumbered 90-92 in June 1938. The others had all been scrapped in 1931.
The class was later simpled; see Locobase 298.
Firebox had combustion chamber and 105.5 sq ft (9.8 sq m) of thermic syphons, boiler had feedwater heater. All cylinders were HP; engine was oil-fired.
A middle-era articulated with simple expansion all around,, this class consisted entirely of rebuilt N1 mallets (Locobase 15054). They were superheated and simpled beginning in January 1929 and ending in December 1931.
Previous number Number as N-3
The entire N3 class was renumbered yet again in 1938 to the 50-66 range.
Like its predecessors, the N3 had low drivers, but their firebox heating surface area was considerable as was the superheat area as a percentage of combined heating surface. Jim Scribbins (in Drury, 1993) notes that these engines had the highest tractive effort of any Milwaukee Road (by then the Chicago, Milwaukee, St. Paul, & Pacific) class.
|Specifications by Steve Llanso of Sweat House Media|
|Railroad||Milwaukee Road (CMStP&P)||Milwaukee Road (CMStP&P)||Milwaukee Road (CMStP&P)|
|Number in Class||25||11||17|
|Road Numbers||5000-5024/9500-9524||1650-1654, 5025-5029, 9105-9110||9300-9316 / 50-66|
|Locomotive Length and Weight|
|Ratio of driving wheelbase to overall engine wheebase||0.21||0.21||0.21|
|Overall Wheelbase (engine & tender)||79.69'||80.23'||80.23'|
|Axle Loading (Maximum Weight per Axle)|
|Weight on Drivers||323500 lbs||327500 lbs||323800 lbs|
|Engine Weight||390000 lbs||396000 lbs||390300 lbs|
|Tender Light Weight||165700 lbs||166900 lbs||349300 lbs|
|Total Engine and Tender Weight||555700 lbs||562900 lbs||739600 lbs|
|Tender Water Capacity||9000 gals||9000 gals||18000 gals|
|Tender Fuel Capacity (oil/coal)||14 tons||14 tons||7300 gals|
|Minimum weight of rail (calculated)||90 lb/yard||91 lb/yard||90 lb/yard|
|Geometry Relating to Tractive Effort|
|Boiler Pressure||200 psi||200 psi||200 psi|
|High Pressure Cylinders (dia x stroke)||23.5" x 30"||23.5" x 30"||21.5" x 30"|
|Low Pressure Cylinders (dia x stroke)||37" x 30" (2)||37" x 30" (2)|
|Tractive Effort||70418 lbs||70418 lbs||82718 lbs|
|Factor of Adhesion (Weight on Drivers/Tractive Effort)||4.59||4.65||3.91|
|Firebox Area||372.60 sq. ft||342 sq. ft||451.50 sq. ft|
|Grate Area||72.20 sq. ft||72.20 sq. ft||72 sq. ft|
|Evaporative Heating Surface||6555 sq. ft||5240 sq. ft||4849 sq. ft|
|Superheating Surface||1030 sq. ft||1193 sq. ft|
|Combined Heating Surface||6555 sq. ft||6270 sq. ft||6042 sq. ft|
|Evaporative Heating Surface/Cylinder Volume||435.25||347.94||192.33|
|Computations Relating to Power Output (More Information)|
|Robert LeMassena's Power Computation||14440||14440||14400|
|Same as above plus superheater percentage||14440||16750||17280|
|Same as above but substitute firebox area for grate area||74520||79344||108360|