The Alco DL-531 was mentioned early in this thread, and was evidently part of an expanded export range announced in 1956 October.
In a general sense, it could be said to have been comparable to the EMD G8 and the GE U9B/C, thus falling into the category of a light road locomotive of compact dimensions and of around 900 hp. In the EMD and GE cases, their respective models were simply their next larger sizes of around 1200 to 1300 hp, the G12 and U12B/C, fitted with less powerful, lower-cylinder-count engines. So they may have been a bit longer and heavier than strictly necessary for the role, but the commonality no doubt helped keep production costs down.
Alco was in a different position, in that it did not have a “next-size-up” locomotive because at that time it did not have an engine intermediate between its 6-251 and 12-251 models. Thus of necessity its 900 hp export model was essentially a standalone design. That being the case, it appears to have made this a virtue by producing a locomotive that was a bit shorter, and a bit lighter than its American competitors.
The DL531 was 42’0” over end-frames, as compared with 43’0” for the EMD G8 and 46’4½” for the GE U9B/C.
I haven’t seen a definitive baseline weight number, but 150 000 lb for the CM-gauge C-C version is my best estimate. The CM-gauge A1A-A1A version of the EMD G8 (there was not a C-C option) started at 156 000 lb (back-calculated from the quoted minimum axle loading), and the GE U9C at 170 000 lb.
In profile, the DL531 was essentially the same as the GE Universals, namely 12 ft high and 9 ft wide, although specific railroad variants were sometimes higher and/or wider. The EMD G8 and G12 were 12’2” high and 9’2” wide.
The DL531 powerplant was the established Alco 6-251 engine and GT584 main generator that had previously been used in Alco domestic market switchers and a couple of GE models including the White Pass & Yukon shovel-nose units. The GT584 was fitted with a belt-driven auxiliary generator-exciter combination. There has been some discussion of the relative merits of gear-driven vs. belt-driven auxiliaries in the GE Export thread; the empirical evidence is that whilst the former was preferred for higher output road locomotives that operated at habitually high load factors, the latter was acceptable for switching and lower-powered general-purpose locomotives. Lower first cost, lower weight, and easier (if not more frequent) maintenance and repair may have been factors.
So established practice was weighted in favour of retaining belt-drive for the DL531. Space considerations might have been a factor as well. The DL531 as laid out did not appear to have had room to accommodate a main generator with gear-driven and overhung auxiliaries, although that is not to say that a different positioning of equipment could not have been used. Presumably Alco would have had access to the GT599 main generator, with gear-driven auxiliaries, that GE had developed for its own U9B/C. Developing a variant to mate with the Alco engine should not have been a problem. The inference is that on balance, Alco did not consider the extra complication justified for a locomotive in this class. As well as with the standard GE761, the DL531 was also available with GE764 motors for three foot gauge applications.
In the late 1950s, there was a market for this kind of locomotive, and the DL531 sold quite well in that period. The EMD G8 also sold reasonably well, but was noticeably outsold by the more powerful G12. The GE U9B/C had minimal sales, whilst the U12B/C did very well. So the "next size up" was perhaps an even more important market sector.
So it is not surprising that, as recorded by Steinbrenner (page 405), Alco saw its lack of an intermediate power export locomotive as a problem that needed a solution, hence the DL535, released late in 1961. Given that Alco did not then have an eight-cylinder version of the 251 engine, its only recourse was to uprate its 6-251, to 1350/1200 hp. It would be a few years before the same higher per-cylinder output was applied to the 12- and 16-cylinder variants, so it was something of a bold step. On the other hand, it was a lowish risk move, since arguably the bottom end at least of in-line six was less stressed at a given per-cylinder output than were the vee versions.
The DL535 had a longer frame than the DL531, at 45’4” as compared with 42’0”. This made it just a foot shorter than the GE U12B/C, which had become the U13B/C by the time that the DL535 was released. In part this extra length was required to accommodate a larger cooling group for the higher output engine. The higher power required a larger main generator than the GT584 used on the DL531, and Alco chose the GT581, which is also what GE had used for its U12B/C. However, Alco elected to retain belt-driven auxiliaries as had been used for the DL531, and this necessitated the development of a special version of the GT581, as hitherto that had been built only with gear-driven auxiliaries, and was used by Alco in that form for its larger locomotives. In isolation that could be seen as a retrograde step, but Alco evidently chose the arrangement that it saw as being best for this class of locomotive, even if it meant introducing a new part. Base weight was 158 000 lb, quite a bit lighter than the 177 000 lb that GE quoted for the U13C (1420/1300 hp) and the 190 000 lb for the EMD GR12 (1425/1310 hp).
Indian Railways (IR) was the first customer for the DL535, and to some extent that model might have been designed around the IR requirements for a light metre-gauge locomotive. In particular its restricted overall height of 11’1” looks to have been of IR origin. And presumably IR had wanted something more conventional than the rather odd EMD GA12 acquired previously. The DL535 was the IR YDM4 class, initially supplied by Alco and MLW, but later home-built by DLW Varansi, with quite a few exported to places such as Tanzania and Vietnam.
Returning to the DL531, here is an equipment layout diagram:
Alco DL531 Layout.gif
And this diagram shows the dimensional differences for the Australian version built by licensee Goodwin. These differences were mentioned earlier in this thread.
Goodwin-Alco DL531.gif
There were some dimensionally different DL535 variants/derivatives, about which more next year.
Happy New Year!
