Multiunit steam?

[DSchmitt]

One eary reconized advantage of electric and dieselelectric locos over steam is the ability to MU when properly equipped. Did anyone ever figure out a way to MU steam? If it is possible, who developed it? When? How?

[AltonFan]

Steam was MUed, with each steam locomotive having its own crew, and communicating by means of whistle signals. I never heard of multiple steam locomotives communicating by means of radio or telephone, which certainly would have been possible in later steam days. I don't think it was possible to operate multiple steam engines with only one crew.

The proposed ACE-3000 was supposed to be capable of MU-ing with diesels. I've also heard that some steam locomotives in excursion service have had equipment installed to at least facilitate steam and diesel operations. But the technology that makes this possible became available only after steam had been retired.

One wonders what could have been accomplished had steam locomotive builders had modern electronic, remote control, and monitoring equipment available. But then, it is easier and cheaper to apply all this stuff to a locomotive that runs on electricity.

I suppose one problem would have been the suspicion engineers and firemen have of not being able to directly monitor boiler water levels. I understand this issue hampered development of "automatic" steam locomotive control systems in the 1930s.

[Overmod]

Alton mentions steam MUing to diesels. This has, in fact, been done on a number of steamers, but consists of installing diesel-type controls in the locomotive cab. These aren't coordinated to the steam throttle, reverse, etc., and therefore (to me) don't constitute 'true' MU in the sense Frank Sprague intended...

A rather 'easy' method of doing MU, if there is only one steam engine in a consist and it is always leading, is to put an appropriate sensing system on the tender drawbar and use that to control the following diesels. It helps to add a speed signal from the steam locomotive -- NOT taken from the drivers! -- and a few other things like a detector for independent-brake actuation. IIRC there is some published discussion about this sort of thing.

Steam-electrics are inherently *capable* of MUing -- the original UP GE steam-electrics being a good example of the technologies required. The problem would be to develop controls that duplicate *diesel-electric* ones (Run 1 to 8, for example, for EMD 'compatibles', or whatever the early Alco air systems used). Steam motors have very different torque vs. load characteristics vs. diesels. This makes it comparatively easier to design generator and motor controls -- BUT also requires that MU signals to and from diesel locomotives are 'remapped' appropriately. In the good old analog days of the '40s and '50s this would involve substantial hardware and tinkering. Cheaper just to buy more diesels, especially if financed via equipment trust...

Ordinary steam locomotives are a much worse proposition. Their engine controls are radically different from diesel-electrics, and require much more power (and mechanical travel) to move. Consider how slip recovery would be made on a trailing steam locomotive. Again, remember what compatibility with early diesel controls would involve.

The really big issue here, for me, is legal and political liability for the firing and feedwater considerations. Unattended firing on a large conventional firetube boiler *in locomotive service*was an invitation to disaster even before September 11th. Yes, I know automatic water controls have been in use on boilers of comparable size and steam-generation rate for many years, and yes, I know they can be easily adapted to changing grade profiles that shift the apparent water level. No, I wouldn't trust them to be 100% successful at keeping water over the crownsheet. (I omit a discussion of maintenance and operating practices -- particularly traditional ones -- here, leaving these solutions for the reader ;-})

The comparable risk of explosion for a diesel of comparable horsepower rating is...???

To me, this implies you'd want a crewmember on each trailing steam 'unit' (unit using a conventional boiler, that is) to keep an eye on the automatic systems and the state of the firing. Might be a useful way to make 'three-man crews' less odious to railroads, provided the BLE, UTU et al. could be induced to accept it...