Talk:Duplex locomotive

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I Added link to austrian locomotive Duplex. It uses similar principes as here described locomotives, but 70 years before them. I dont know, how to add it to this article. --Postrach 09:25, 17 October 2006 (UTC)

A successful french duplexEdit

In France the duplex type was made famous by the ten 2-4-6-2 (151 A) compound locomotives built in 1932 for the Paris-Lyons-Marseilles company (PLM) to haul heavy goods-trains on the 1/125 gradient between Les Laumes and Dijon.The performance was so good the company wanted to order more engines but the nationalization of the railways (1938) stopped all projects. These duplex engines were fitted with Lentz-Dabeg rotary cam valve motion and soon with double exhaust. The LP cylinders drove the first coupled axle.

(Apologies, but: - Investigation on Google (try 'PLM 151A') will reveal photos. The front (LP) cyls drove on the 2nd coupled axle. For the record, the rear (HP) cyls drove on the 5th coupled axle.)Herbgarratt (talk) 23:50, 18 May 2009 (UTC)

The driving wheels had a diameter of 1.50m (4'11").The highest permissible speed was 53mph. In a test on December 19,1933, the engine developed slightly more than 3000HP at the drawbar for a distance of 37 miles at a speed of at least 46mph, and that without being overworked. In ordinary service the engines could, while hauling 1375 US tons, sustain a speed of 31mph at the summit of the 1/125 Blaisy gradient. The 151 A were withdrawn in 1956 and scrapped.Blaisy 12:11, 20 February 2007 (UTC) 10:36, 27 February 2007 (UTC) 11:34, 8 March 2007 (UTC)

The recent controversy regarding this locomotive -- which is indeed NOT a 'duplex' by Johnson's (or Emerson's) definition of the concept -- points up the importance of expanding the general subject of 'duplex locomotives' correctly. As a start, I suggest incorporating the following:

1) The introduction needs to cover some of the trends in locomotive design leading up to the introduction of the duplex concept. I would include (in United States practice) the brief use of three-cylinder simples for higher-speed freight power (notably at Alco) and Baldwin's short-lived experimentation with high-pressure and compounding (locomotive 60000 of 1926) to see why the concept of 'all outside cylinders' with no connection between 'engines' was what Johnson supported.

2) The discussion of balancing seems somewhat confused, perhaps indicating that its original author doesn't quite understand the difference between (for example) cross-balance and overbalance; hammer-blow is an almost-inevitable consequence of inertia of rods on quartered locomotives, and NOT just of a portion of the reciprocating mass as stated -- reciprocating imbalance contributes primarily to surging in the longitudinal plane, not vertical coupling through the suspension. Unless this distinction is made, the reason for dividing the drive rather than simply placing four outside cylinders on a coupled driver wheelbase won't be particularly clear.

3) A whole, important section on duplex design is omitted -- that being the discussion of 'conjugated duplexes' (of which the PLM 151A is a member). This discussion would begin with the Riley Deem proposals for mechanical conjugation of the units of a duplex locomotive, for example by hypoid gearboxes and a longitudinal conjugating shaft passing under the rear cylinder casting (this method chosen to avoid weakening the engine bed by making provision for inside conjugating rods/cranks). It might then continue with discussion of the Withuhn conjugated duplex of the early 1970s, as discussed in Trains v34 n8 (Jun 1974) pp36-47, and then (of course) with that concept's practical application in the ACE3000 locomotive proposal of the early 1980s. Some discussion of the 'pros and cons' of rigid conjugation vs. using a device such as a Ferguson clutch to permit the two 'engines' to work separately when one of them is not slipping could be incorporated in this section, as can the discussion of 'phasing' the two conjugated units at 45 degrees, rather than the 90 degrees of Withuhn's approach, to get better torque-peak characteristics per revolution at the cost of a certain (perhaps tolerable) amount of imbalance (cf. Kiefer's "A Practical Evaluation of Railroad Motive Power", New York, Steam Locomotive Research Institute, Inc., June 1947, p.8 for magnitude and speed involved)

4) Perhaps an accurate taxonomy concerning the term 'divided drive' ought to be made at some point. Divided drive with NO coupling between 'engine' units is a (required) characteristic of Johnson's and Emerson's original designs (the difference in phase between the two being intended to 'break' a tendency toward augment at very high speed). Divided drive conjugated OUT of phase (as on the PLM 151A and the Withuhn duplex) deserves its own name, but "duplex" by itself should not be that name. (Further consideration might be made regarding compound v. simple steam distribution, particularly where timing between HP and LP is considered important and/or the phase between HP and LP "engines" is fixed out of strict 180-degree opposition to improve power or dynamic reciprocating balance.) Proposals that put multiple cylinders on a coupled wheelbase, e.g. to reduce main-pin forces or (as on the last of the D&H high-pressure compounds) to facilitate multiple expansion with all outside cylinders, are not in the 'duplex' category at all.

This might be considered analogous to the taxonomy of articulated locomotives following the Mallet pattern. By definition, all "Mallets" are compound, because that was explicitly part of Mallet's intention and patent. A significant proportion of the engineering and railfan community therefore accepts the term "simple articulated" to describe a 'Mallet' locomotive using simple expansion; similar rigor could gainfully be employed here.

Wizlish (talk) 08:35, 20 May 2009 (UTC)

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Re the PLM 151AEdit

All 'Duplex's under this Wiki page, except the PLM 151A, have no mechanical/torsional coupling between the two power units, both of which are in the one rigid frame.

It appears implicit that the 'Duplex' concept, as innovated by Ralph P Johnson, excludes any such coupling between units. While there has been much debate as to whether or not such inter-coupling would have been advantageous, it was never included.

The PLM 151A is coupled throughout its 5 driving axles. The 2nd and 3rd coupled coupled axles are coupled by *internal* coupling rods, working on two quartered inside crankpins.

Thus, one suggests that the PLM 151A is a 'divided drive' 2-10-2, not a 'Duplex' 2-4-6-2? —Preceding unsigned comment added by Herbgarratt (talkcontribs) 13:39, 18 May 2009 (UTC)

Additional candidates for "Duplex" locomotives?Edit

Referencing this page:

there are three locomotives that are, or were, related to the Duplex Locomotives page.

As noted in the 'talk' discussion for 'locomotive duplex', the Haswell locomotive of 1862 is not a 'Duplex' in Johnson's terminology (and by reference to the graphic, we can see clearly why this is not so). It is a balanced design, with two outside cylinders working 180-degree-opposed cranks on each side (with the sides presumably 'quartered' 90 degrees relative to each other).

The James Toleman (1892) is a divided-drive locomotive that (imho) fails the 'duplex' test because

a) only two of its four cylinders are outside; and b) all four cylinders are ahead of the drivers (a very long piston rod being used to reach a rear-mounted crosshead (which I believe was used to allow all four main rods to be equal in length).

This design might be compared to the George Strong 4-4-2 of a decade earlier, which used a double crosshead to drive two separate main rods on otherwise-uncoupled drivers.

There is also a picture of the Petiet 441 for the Chemin de Fer du Nord (1862) -- see also

which is difficult to express in Whyte notation, and even in German style can be confusing; the design clearly passes the 'Duplex test' in that we have outside cylinders, unconjugated drivers, and a rigid frame. I don't think, however, that Johnson or anyone else would have envisioned putting even single carrying wheels INSIDE the effective driver wheelbase... let alone three of them (and if I understand correctly, these are three separate axles presumably with LOTS of lateral motion but no radial compensation).

Wizlish (talk) 00:58, 22 May 2009 (UTC)