Talk:Mallet locomotive

Untitled
The diagram of the Mallet locomotive articulation is wrong. The front engine (not strictly speaking, a bogie) must translate laterally, otherwise it will derail on a curve. The wheels must describe an arc. It does not simply pivot on the locomotive centreline at the front engine centre as indicated. It must be allowed sideways play, provided by a pivot a long way from the centre, or by a bar linkage, or a pin, sprung to centre in a slot. In Baldwin Mallets, the pivot was usually near the rear, high pressure, cylinders on the fixed engine. The two carrying bogies on the diagram are irrelevant to the Mallet design: the rear one as drawn is incorrectly pivoted for the same reason as above; the front one is broadly correct. Two four-wheel engines would be sufficient to illustrate the concept.

The diagram also needs rails and some labels; a non-technical viewer cannot be expected to understand what is shown, because it does not say it is the underside of a locomotive on a curve, and the curved rails are not shown.

Verifiable references: Robins J G, 1973, World Steam Locomotives, Bartholomew ISBN 0851529232 illustrated the original 1887 Mallet articulated 0440 http://www.ironhorse129.com/prototype/Mallet/Baldwin65/Design.htm (last accessed 12/3/06) illustrated Baldwin's comparison to the Fairlie with illustrations from Baldwin Record 65

kind regards

Andrew Starr, Manchester UK


 * The diagram has been replaced with one that is more accurate. Hellbus 15:15, 30 September 2007 (UTC)

Purists claims
I have seen references in US publications to compound mallets being described as "Mallets" and simple mallets being described as "articulateds" (as if there were no others), with a clear distinction between the two. If I come across a source I will add it. Otherwise it is not a particularly important point. --Michael Johnson (talk) 02:00, 13 February 2008 (UTC)

According to "Those Amazing Cab Forwards" by George H. Harlan, Southern Pacific was careful and rigorous about the use of the terms "Mallet" and "Simple Articulated". Mallet, for them, was a compound locomotive, with a set of high pressure cylinders and a set of low pressure cylinders powered by the exhaust of the high pressures. In a simple articulated, all cylinders received the same steam pressure. They'd found that at the limit of power and traction, only the high pressure cylinders were really providing much tractive effort, so they switched. They were fairly strict about nomenclature: early articulateds were MC-1 through MC-6,standing for "Mallet Consolidation", or 2-8-8-2, and later locos were AC-1 through AC-12, for "Articulated Consolidation". AC-4 and later were actually 4-8-8-2. All Mallets were either scrapped or rebuilt as simple articulateds. — Preceding unsigned comment added by Hans42 (talk • contribs) 06:39, 17 April 2011 (UTC)


 * Of course their care about the distincton was due to patent liabilities; Mallet insisted on his patented designs being compound, so if you buiilt a simple expansion locomotivve and didn't call it a "Mallet" you could avoid paying him royalties. Afterbrunel (talk) 14:05, 13 August 2012 (UTC)
 * Well, that, and the SP didn't have any articulated engines that weren't Mallet style articulation, so it made sense for them to call them Mallet and simple; there was no risk of confusion with other types of simple articulated engines (the SP did have a Shay, I think, but in US practice those are not usually considered articulated, LeMassena notwithstanding).

Dubious
I'm a bit dubious about the claim for the Virginian engines. Can we find a reference that is actually accessible on which to base this? Mangoe (talk) 19:53, 13 August 2012 (UTC)


 * Well, I cited the reference, of which I have a copy here. All it says is that three locomotives pushed a big train. It doesn't even state a gradient. Is that so implausible? Afterbrunel (talk) 08:56, 14 August 2012 (UTC)


 * Looks like Reed got that one wrong. Far as anyone else knows VGN got the 2-10+10-2s for the 2% climb out of Elmore; Rwy Age for 7 June 1924 says they ran 5500-ton trains up there with the two 2-10+10-2s shoving, then 2-8+8-2s handled the trains Princeton to Roanoke. Doesn't says anything about east of Roanoke, but I'm guessing no reason to run 2-10+10-2s on the 0.2% grade there. (And I'm guessing Reed wasn't talking about after the 1925 electrification.)Tim Zukas (talk) 17:36, 23 August 2012 (UTC)

Bissel Truck
I'm dubious about referring to the front engine as a "Bissell truck". While conceptually you could call any set of wheels and frames which pivots at one end a Bissell, the term is usually used to refer to two wheel leading trucks (pony trucks) and two or four wheel trailing trucks of the Cole or Delta type (as opposed to the center pivoted type sometimes used on tank engines). None of the references I have, either steam era or modern, call the front engine of a Mallet a Bissell. I'd suggest the article should be amended to more clearly describe how the front engine pivots on the rear, and eliminate reference to a Bissell truck.

Also, in the section on simple locomotives, it says the high pressure steam pipe "passes thru the truck pivot pin". This is wrong, both in that the steam pipe obviously does not pass thru the pin (on locomotives using this routing the pipe passes above the pin - incidently the same routing was used on the C&O compound locomotives), and in that many simple locomotives did not route the high pressure steam forward from the pivot pin, but instead used a direct routing (more or less - two swivels and a sliding section isn't exactly direct) from the smokebox to the front cylinders. Suggest either this be expanded to correctly describe the routing, or simply remove the misleading comment. — Preceding unsigned comment added by 2001:558:6030:44:1B6:90A5:EC7A:E5A6 (talk) 23:06, 19 June 2014 (UTC)
 * Of course it's not a Bissel truck. The characteristic of a Bissel truck is a single axle, with a single pivot offset axially from this. The Mallet bogie is similar, in that it's a single pivot with an axial offset, but it's not a single axle and that's defining for the Bissel truck. Andy Dingley (talk) 21:17, 2 November 2019 (UTC)

Assessment comment
Substituted at 22:55, 29 April 2016 (UTC)

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Disadvantages.
Can some info be added to the article about why compounding was not used very much? Other articles I've seen about engines often have a "disadvantages" section. ColinClark (talk) 19:02, 30 May 2018 (UTC)
 * The article structure isn't too bad, but it's (as always on WP) a bit trainspottery and short on actual explanatory narrative.
 * The Mallet began in Europe, as compounded tank locomotives. This was Mallet's original concept and worked as he'd planned. The first of them were for Decauville systems, quite small, but needing flexibility to handle tight corners and poorly laid track. As they grew larger in Europe, some countries started to use tender Mallet designs. These lost some of the adhesion advantages, but kept the compounding.
 * In the USA, they grew huge. The limitations of the Mallet design started to become evident. The front overhang was unworkable, but slow US freight speeds managed despite. The lack of adhesion for these super-power locos produced things like the Triplex Mallet, to keep up adhesive weight. Even then, the axle load was becoming poorly distributed and the central HP group was doing much more of the work, both from its power and also because the others were prone to slip.  Finally the limits of compounding were reached and they started to become simples - either (no-one can agree) the LP cylinders were too big to fit, or else the long, convoluted steam passages to them became too restrictive.
 * The US hung onto the Mallet too long and made them bigger than the range for which Mallet's system worked. Europe had gone in other directions, such as the du Bousquet and returning to the Meyer. Manchester had invented the Garratt, twenty years after the Mallet, and developed this for the large examples in Africa and Australasia. For the locomotive sizes being built in the US, these would have been a much better design. Although Garratts were pretty much never compounded, for simplicity, larger ones could easily have been three or four cylinder compounds on each unit, without piping problems.
 * I don't see compounding as being too related to disadvantages. Disadvantages for the Mallet were many, but mostly related to the excessive size of the later US ones. Anything that involves articulating a boiler barrel has grown too big. Andy Dingley (talk) 12:39, 31 May 2018 (UTC)

Were the low-pressure cylinders & drivers always in front of the high-pressure counterparts?
Were the low-pressure cylinders & drivers always in front of the high-pressure counterparts? Put another way, were the low pressure components always at the opposite end of the Mallet from the firebox? (I do not know.) Let's answer this, in at least a sentence in the article. Acwilson9 (talk) 22:03, 27 February 2021 (UTC)

Big Boy is (not) a Mallet
Some people like Grachester believe that the Big Boy is a Mallet, but this is false. Anatole Mallet's articulated locomotive used compound expansion (high and low pressure cylinders). The Big Boys are simple articulated and used simple expansion (the same pressure in all four cylinders) and therefore they are not Mallets. (NOT MY OPINION) Aitraintheeditorandgamer (talk) 20:50, 5 June 2023 (UTC)