Articulated Steam Locomotives of North America

There's a good film here about the Big Boys, made in the 1960s. There is a discussion, starting about 6min in, of the development of larger locos in the US which, after explaining about Mallet's being articulated and compounds, includes the line (about the Challengers) "Unlike the Mallet, the Challengers use only high pressure steam" - i.e. explicitly distinguishing them from Mallets, despite the articulation.

(Also, starting about 8'35, a view of a 9000 engine, in which for a few seconds round about 9'04 you can make out the combination lever of the Gresley valve gear, which runs unprotected across the front of the loco).



Tom

 

I've posted this picture elsewhere but this is the similar arrangement on the preserved NSWGR Class 57 4-8-2 at Valley Heights, NSW



Despite the problems of three cylinder locos starting a heavy train these locos were built as slow speed sloggers primarily to lift heavy coal and other freight on the 1 in 30 grades over the Blue Mountains west of Sydney.

Peter

 

Bill Withuhn also gives an explanation of why all high speed articulated locomotives had to be simple expansion. Without a train or downhill with one, the Y5s (and Y6s) ran easily at 50 mph, blistering for a Mallet. Their 58 inch diameter drivers, however, were sized for piston speeds and steam flow to give maximum horsepower at 20-25 mph on the three tough eastbound grades to the summits at Bluefield, Christianburg and Blue Ridge. The A class, on the other hand, was intended for highest horsepower at 30-60 mph - with emphasis on the latter speed. To run that fast at maximum power, compound steam locomotives with three or more cylinders needed all valves and cylinders to cycle in perfect concert on one set of inter-connected driving wheels so thaat valve timing for all cylinders could be synchronised. In a Mallet, pressure in the receiver (from high-pressure exhaust to low-pressure inlet) could vary in unpredictable ways, since the two engine units were independent. For the four-cylinder articulated arrangement, high-speed steam utilisation was effective only with simple expansion.

 

English, without a doubt!

 

Alfred Bruce (who was a design engineer at ALCO) in his 1952 book "The Steam Locomotive in America" says on p.78 "The term Mallet should be used only to designate articulated compound locomotives." Locomotive Cyclopedia tends to use "Mallet Compound Articulated Locomotive" and "Single Expansion Articulated Locomotive" to describe the two types. The attached page from Locomotive Cyclopedia (1930 edition) gives some justification for the simple version although as LC was written largely by manufacturers, it tends to be a bit self-serving.

 

Very agricultural, but I guess the slow speed and massive construction reduced the flexing/whip which seems to have been a problem for the LNER locos.

 

Quite correct! But I am using the nomenclature that is used by the book which tends to lump simple and compounds together, particularly as the book also covers Shays, Fairlies, Climaxes, Heislers, and the odd Garrett.
Anatole Mallet himself was a little put out by the fact that the Americans tended to prefer simple "Mallets" and there is also the problem that if one was to use the term Articutated Locomotive that doesn't identify which!
It was only the N&W that really persevered with the compound principle managing to overcome the imbalance in power produced at rail by each engine by designing a valve that allowed the driver to introduce some unexpanded steam into the front "simple" cylinder.
As the compounds and samples are pretty much identical in looks (apart from cylinder sizes) I can see why the term has been used in a lazy form. (Simple Mallet - bit of a mouthful)
In addition many American companies converted compound Mallets to simples without changing the engine layout so sorry I will continue to be lazy!



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I don't think that you will find too many Mallets that were converted to simple expansion. For a start, a much bigger boiler would have been required for which there wouldn't have been space. For instance the boiler used on the N&W Y6 was actually smaller than that used on the N&W J.

Mallets were usually used for heavy, slow-running freights; normally, with the exception of the Y6s, they weren't suitable for running at faster than 30mph because of balancing problems caused by their large LP pistons and the fact that they had separate unsynchronised power units. Simple articulated locomotives were used for higher speeds. The former were more economical for slower freights and the latter were the only articulates capable of high speed running. So unless there was a change in requirement, there was little or no incentive to convert from compound to simple expansion.

 

As I have said before I am working from memory typing the last comment whilst waiting for 14 tonnes of Flaked Maize at Henry Bell's Mills
But Compound Mallets were certainly converted but how much was involved the book does not say. But, sic " by converting its worn out articulateds to single expansion, the railroad produced a locomotive adapted to service over the non-electrified mainline between Aver, Idaho and Othello....." ( 9300-9316 2-6+6-2 Chicago, Milwaukee and Puget Sound)

Great Northern Nos. 1950 - 1984 2-6+8-0 Baldwins : sic "All rebuilt to single expansion type 1926 - 27"

Oregon Railroad and Navigation Co. sic. "Beginning in 1936 the Union Pacific inaugurated a program of converting its 2-8+8-0s to single expansion; and, in that same year, those of its subsidiary were similarly rebuilt".

Southern Pacific sic "1927, when the SP's shops commenced a 12 year program of rebuilding all of its articulated engines, converting them from compound - expansion to single - expansion".

Other examples of other RRs converting are noted in the tome!

Its apparent that the North American Railroads had taken the Mallet to their hearts and were willing to spend time and money, particularly on earlier incarnations, trying to perfect the beast!

 

Watching one of these slogging upgrade through the Lithgow Rat Holes must have been something!

 

Suddenly remembered I have a print of a painting by Artist Phil Belpin. " Down Amongst the Rat Holes"
Not sure I am allowed to post the image so have posted a link.

https://infobluemountains.net.au/review/book/fsam.htm

 

It's very confusing using (incorrectly) the term Mallet to describe a simple articulated locomotive because you don't know whether it's compound or simple expansion, unless stated. The misuse of the word by the Americans, including Bill Withuhn, doesn't make it correct.

 

At least you've got a 50/50 chance, much less confusing than just using 'articulated' You get even closer if you just use 'simple Mallet'. Is there actually a term coined to describe a locomotive articulated in Mallet's style, but using the steam in simple expansion? If not, what's wrong with 'simple Mallet'? 'Kitson-Meyer' seems to be accepted as a term to describe a type that is an evolution of the original 'Meyer' principal.

Anyway, I had a question relating to the original post for those more knowledgeable. Assuming you've got a boiler that can provide an ample supply of steam and the power to overcome the mechanical drag and air resistance, what is the limit to the top speed of a conventional steam locomotive? Does there just come a natural point where the velocities of the reciprocating masses mean that there is physically not enough time in a valve event to admit steam to the cylinders in the required quantities, or just the stopping before the valve gear or connecting rods blow themselves apart?

 

I believe that both Alco and UP described Challengers and Big Boys as simple articulateds and not simple Mallets. If that is what the builder and the owner called them that surely is the correct terminology.

Peter

 

It depends on the locomotive. A Mallet would be limited by the reciprocating masses of the LP pistons and that the HP and LP units weren't synchronised. For others, valve event timing shouldn't be the limiting factor because, with increasing speed, there would be more valve events per unit time. However, the air resistance will increase with the square of the velocity. Valve movement will also be limited by the inertial forces involved; above a certain limit, failure will occur. Lubrication may also fail at high speed.

 

Good question but why do there have to be reciprocating masses? The answer might lie in a steam turbine drive, a la Turbomotive.
Some sources have quoted it was quite well thought of but suffered from the application of new (for rail traction) technology and subsequently war.

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I could stir things up by saying "who cares"?
It is a bit like how non railway enthusiasts call a locomotive a "train". We know that's wrong but live with it because life is just too short. (And don't want to appear anoraks)
Now ducks to avoid the flak

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Not really. Just look at the relative size of the bally cylinders!

 

You are probably right but if someone just wants a speed record it is one way to go.
Different type of turbine but Leyland in the 1960s (and others) looked at utilising gas turbines in Lorries. The final drive was through a gear box to reduce the speed of the output shaft - approx 30000 RPM, to something more manageable at the wheels.
And didn't several railways run gas turbine Locomotives ? And the N&W produced a steam turbine/electric Locomotive the "Jawn Henry".

https://en.wikipedia.org/wiki/Norfolk_and_Western_2300

Seems the C&O were at it as well. If diesel technology had not taken hold so readily who knows what could have transpired?