Compound engines

Who knows what was the last main class of compound steam engines on American rails?
I know, that B&O ordered the last compound articulated after the II.WW but it was an exception.
(Compound means high and low pressure cylinders in a single locomotive).
I guess this technology was obsoleted sometimes around 1920.

Not the B&O-- it was the C&O that got 10? compound 2-6+6-2s around 1949. The last compounds built in the US were 30 N&W 2-8+8-2s in... 1950?

So, maybe Mallet articulateds are a special case. When was the last compound locomotive built for U.S. service that WASN'T an articulated. (I don't know the answer. Certainly Baldwin 60000, the 4-10-2 demonstrator now in the Fr4anklin Institute in Philadelphia, was late in the U.S. history of compound steam.)

I wouldn't say the technology was obsolete. Countries more interested in efficiency than the U.S. -- France, for example, with much poorer coal reserves -- continued to build compound steam locomotives even after WW II. Many people would say that the high-point in steam locomotive technological development was the 242A1, a 3-cylinder compound 4-8-4 designed byAndré Chapelon and built post-war.

There was a trade-off. Compounds were more efficient, but needed more maintenance attention. In a country with more fuel than it knew what to do with but relatively high wages, compounds would be replaced by big but crude brutes of locomotives. In a country with lower wages but less coal... In France, the last steam locomotives in mainline service tended to be simples: I don't have statistics at hand to ce sure, but I'd be willing to bet that French wages for skilled blue-color workers increased dramatically between the end of the war and the end of steam.

Thank you for the answers.


ad Timz. I read somewhere and the the B&O machine was the last articulated compound (based on design from 1920-s)

In the museum in Baltimore.

ad Allen

I wouldn't say the technology was obsolete.

That is correct, in my starting question I had only USA on mind. Here in Europe, as you also wrote, where many compound constructions till the end of steam era.

Last non-Mallet compound built in the US: got to be either the NYC 4-8-4 or the D&H 4-8-0? Both around 1930.

The three D&H compounds, the BLW 4-10-2, the NYC 4-8-4-- all experimental one-offs. What were the last non-Mallet compounds built in the US that actually got used in regular service for some years? Probably the SFe 3500-class 4-6-2s from about 1914 (35 engines-- all converted to simple by 1923? or so).

The C&O (*) mallet was the last compound built for an American railroad by a "commercial" locomotive builder (Baldwin): Norfolk & Western's later Y6b 2-8-8-2 Mallets were "homebuilt" (in the railway company's Roanoke shops). The N&W locomotives were in once sense a new design-- they incorporated features not introduced until after WW II-- but in another sense not: they were the result of a gradual evolution and refinement by the N&W of 2-8-8-2 designs that started before WW I.

--

Not even B&O/C&O: the merger came later. I don't remember the exact date of C&O's purchase of a controlling interest in the B&O, but few if any steam locomotives would have been in service by the time it took place. (Grin!)

I wouldn't say compound articulateds were a special case. They were the only kind of compound that was really successful in America.

The last N&W 2-8-8-2s were built in 1952.

In the mid-1920s, many roads started converting their compound articulateds to simple; this was about the same time as the first simple articulateds were built new. The main reason was to allow faster freights. This is the same reason the 2-10-0 and 2-10-2 stopped being built. Most railroads already had more drag freight power than they could now use.

The compound Mallet was good for its purpose: long, slow drags. I can figure why most US articulateds were Mallets: an articulated has to have 4 cylinders anyway, so the simple doesn't have the advantage of simplicity in this case.

The roads to order new compound Mallets after 1930 were the coal roads (N&W, C&O) and logging lines. I believe the last working articulated, and compound, in the US was the last Rayonier 2-6-6-2 in 1968.

Checked out my HO gauge model of a PRR Y-6b compound articulated, a true Mallet. The lead engine's cylinders are considerably larger than the following engine's cylinders. Typical characteristic of a compound artiulated Mallet.