Class N1 (Locobase 15054)
Data from "Powerful Locomotives of the 2-6-6-2 Type", American Engineer and Railroad Journal, Vol 85, No 3 (March 1911), pp. 90-91. Works numbers were 48838-48854 in December 1910, 48855-48862 in January 1911.
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).
Class N2-s (Locobase 15053)
Data from Roy V Wright (Ed.) 1912 Locomotive Cyclopedia of American Practice, Third Edition (New York: Simmons-Boardman Publishing Company, 1912), p. 189 and 240. See also MILWRD 1930ca Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. Works numbers were 51057-51066, 52124-52129.
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.
Class N3-s (Locobase 298)
Data from tables in 1930 Locomotive Cyclopedia and MILWRD 1930ca and 1945 locomotive diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange collection. See also See also Jim Scribbins, "Chicago, Milwaukee, St Paul & Pacific (Milwaukee Road)" in George H Drury, Guide to North American Steam Locomotives, Revised Edition (Waukesha, WI: Kalmbach Books, 2015), p. 134. (Thanks to Chris Hohl for 13 December 2020 querying the original tender's fuel capacity. )
A middle-era articulated with simple expansion all around,, this class consisted entirely of rebuilt N1 compound mallets (Locobase 15054). Their road use consisted primarily of helper service in the Milwaukee Road's mountain sections.
Firebox had combustion chamber and 105.5 sq ft (9.8 sq m) of thermic syphons, boiler had feedwater heater. All cylinders were HP and used 10" (254 mm) piston valves. Coffin feed water heaters were attached as a distinctive "horse collar" to the face of the smokebox.
The original tender carried 9,000 US gallons (34,065 litres) of water, but key sources show different information for the original fuel. Chris Hohl noted the 1930 Locomotive Cyclopedia's data, which showed an oil-fired engine trailing a tender carryng 3,965 US gallons (15,008 litres) of oil and weighed 165,700 lbs (75,160 kg). Jim Scribbins's commentary in George Drury's guide says that later tenders had double the oil capacity of the original, implying that the engines were oil-fired. But Milwaukee Road's own diagram book shows a tender carrying 14 tons (12.7 metric tons) of coal in a tender of the same weight.
They were superheated and simpled beginning in January 1929 and ending in December 1931.
Previous number Number as N-3
9504 9300
9520 9301
9500 9302
9503 9303
9521 9304
9519 9305
9524 9306
9511 9307
9515 9308
9508 9309
9513 9310
9516 9311
9505 9312
9517 9313
9514 9314
9502 9315
9523 9316
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 confirmed that these engines had the highest tractive effort of any Milwaukee Road (by then the Chicago, Milwaukee, St. Paul, & Pacific) class.
55 (ex-9305) left the road first, retiring in January 1950. 64 went last in May 1954.
