Locomotive MU systems

Trains Magazine Locomotives
1

I must assume that today all makers of locomotives use compatible MU connections, so GE and EMD can work together. And even 60 years ago, I regularly saw EMD and Alco and even FM mixed together, presumably with no compromise. But seems to me in the dim origins, various makers had their own systems and you could not readily mix brands. I know nothing of the details of MU. But I am sure everyone recognized the value of inter-brand compatibility.

SO my question is this: in the early days, did EMD just “win” as the 300 pound gorilla in the room, other makers adapting to their system? (or EMD adopting some other.) Or was an industry committee formed to set up a standard? How long did incompatibilities linger before the industry got it all worked out? And has the modern system evolved? I mean would a 1955 F unit plug into a present day locomotive and proceed? Or are there limits to back-compatibility?

That’s enough questions.

2

There’s a reason the 8-notch system is standardized as ‘AAR’ (and there are reasons it persists long past tilting plates to implement binary relay logic).

Manufacturers have gone far beyond 8-notch engine governing in a number of respects; GE tried for some time to provide ‘intermediate notches’ by tinkering with excitation, for example, and at least some versions of DPU are proportional in servo.

It makes just as much sense to retain interworkable 8-notch (whether you call the notches ‘run’ positions as EMD did or not) as it did for Vail to implement the modern Bell system to be backward-compatible with older equipment and systems for so many years. A modern computer-controlled engine does not need to respond to notch commands, nor does a program like TO or Leader need to convert its commanded speeds into notch settings directly. But it helps if any engine has the ability to control any consist it ‘finds’ itself controlling in MU, and contrariwise can be controlled by anything if necessary.

3

at one time in Panama City Fl. The Bay line (A&SAB) had (or has) an Alcoa Road switcher in a park. The MU connector only had a 19(?) pin connector.

4

Since you are asking about MU cables, I have a question. When I was employed by the PRR in the late '50’s, Diesels had three or four hoses on each side of their pilot and their other end. I was told they were for MU purposes. But the units also had multipin cable connectors. Were the hoses for use with non-EMD units? Or older EMD units?

5

The hoses were for operation of various aspects of pneumatic operations in the MU hook ups. The Cable connections are for the electrical operations involved in the MU hook up - both are required.

6

Some of the really old-time diesels had pneumatic throttles.

7

Baldwin made quite an effort to establish their pneumatic system as better than 8-notch binary. Of course with the tugboat engines, there was enough horsepower at idle to get a light engine close to 30mph on level track… [:-^]

If you look at GG1s, which are straight electrics with transformer-tap throttle control, you will see the hoses involved in MU brake connections. We have discussed what these do in past threads.

A passenger engine would also need a connection of some kind for the conductor’s signal line. We had a thread years ago about a mystery hose from the nose of an early E unit that I think was such a connection.

I thought it would be easy to find ‘manual’ pictures of the connection arrangements for BLW power, or to locate some of Matthew Imbrogno’s comments on modernizing the system for shortline and special use. I am sorry to have failed in this so far. I am sure there are people here, or following the Classic Trains forums, who will know; someone might consult the nooks and crannies of the Bakdwin Diesel Zone site or a Wayback version of it to see what’s there.

8

Recently, while MUing locomotives, I had to explain a quirk of locomotive design to my very new Switchman. The angle cock, found on the brake pipe at both ends of every piece of rolling stock, is open when the lever is in-line with the brake pipe and closed when turned perpendicular to the brake pipe. Makes perfect sense, right? Conversely, and strangely, the valves on locomotive MU air connections, and on the air lines to each truck, are just the opposite – open when perpendicular and closed when in-line. Similarly backwards, the drain valves on the main reservoir air tanks and air dryers are usually, but, oddly, not always opened by turning the knob counterclockwise. Can anyone point to a reason for this arrangement?

Allan

9

The airbrake one is simplicity itself. If there is no air pressure then the emergency brakes are automatically applied. No with the mu hoses it could be that they’re reversed just incase someone mistakenly somehow got one of them hooked up to the main air line of the train. Don’t laugh it more than likely has happened. Well by having the mu and other signal lines the opposite of the air brakes are you prevent any mistakes when coupling up cars or locomotives together.

10

The glad hands on the brake pipe hose and the MU hoses are different sizes. I don’t think it’s possible to cross the brake pipe with one of the MU hoses. You can cross MU hoses, I’ve seen it happen. (Coming off the diesel ramp, no less.)

There’s probably a reason why the different orientations was used. I’ve never heard why, though.

Jeff

11

Were this so, there would have been no disaster at Lac Megantic. The complication – desirable for other operating reasons – is that sharp enough reduction in air pressure automatically applies the emergency brake; low air pressure proportionally applies the service brakes… but as they bleed off, there is no air to resupply them and, more importantly, no air to dump to toggle the emergency application…

12

You can get the MR and trainline gladhands to go together, but you have to twist one hose around 180 degrees, and even then I don’t think the gladhands will ‘lock’ together properly.

I’ve always guessed that the different gladhand orientation was a deliberate choice to prevent 140 PSI MR air pressure from being introduced to things like brake valves that were not designed to handle that amount of pressure.

Every now and then the shops will put the wrong type of angle cock on the brake pipe or one of the MU air lines. So I got in the habit of feeling for the little raised line on the handle that indicates which position is open, I suppose someone could rebuild the angle cock and mount the handle wrong but I haven’t encountered that yet.

13

With some exceptions, all the builders used Woodward governors to control (or help control) diesel engine speed and load. Fundamentally, this created 8 notches and the ability to shut down the diesel engines from the lead locomotive. The MU connector and what pins did what were left to the builders and the roads to negotiate. The railroads often specified what they wanted to the builders, specifically.

The RRs eventaully standardized on the 27 pin MU system, with specifically designated pin assignments. Many of the pins were unassigned or flexibly assigned for future use. (Conrail’s Select-a-Power system, for example)

Sometimes these unassigned pins could create problems. Early in Conrail, they needed to have special jumper cables for EL locomotives because EL used some pins for sanding control that PC (and the others) didn’t.

A good explainer of pin assignments is here: http://www.railway-technical.com/trains/rolling-stock-index-l/diesel-locomotives/us-locomotive-mu-control.html

14

As long as the Woodward flyball governor is back there on the engine, you’ll have 8 engine speeds (and one or two low idle speeds)… and a load regulator to protect the diesel engine from overloading.

15

Our local mechanical trouble shooters have rigged up a hose that has a gladhand that fits the brake pipe on one end, the other end’s gladhand will fit the main reservoir hose. They did this so they could recharge the MR on a dead DP equipped with the air start system. This way they don’t have to get a live engine next to the dead one to restart it.

It comes in quite handy when the mid-train DP has the auto stop shut down, but then doesn’t automatically restart and then the MR bleeds down. That happened to me once. I figured we would have to set over half the train to the other main track to get the head end next to the dead DP. The mechanical guy came out, applied the compromise hose and was able to get enough pressure in the main and the auxilary air start reservoir to restart it.

The bad habit of DPs shutting themselves down, but not starting up again when needed is why I don’t care for the Auto Engine Stop/Start systems. At one time, engines in DP mode weren’t supposed to have the AESS systems active because of that problem. It doesn’t happen everyday, but way more often than it should.

Jeff

16

What about the “MU” cables for what is called train control? Does it use the same identical connectors? Does anyone know how the pins are assigned>?

17

I can’t say that I have ever found a clear-cut statement as to the origin of the AAR 8-throttle notch control and its associated MU system.

The fairly well-known “Trains” 1968 December article (1) stated that the 8-notch control was of GE origin, developed during the 1930s.

In a 1947 AIEE paper by GE (2), in discussing the then-new Amplidyne control system, it was said:

“Standard practice for several years by most manufacturers of diesel-electric road locomotives has established the use of eight throttle handle notches for obtaining eight different engine operating speeds on units which are operated in multiple. The amplidyne excitation control circuits therefore were designed on this same basis in anticipation of probable requests by ultimate customers to operate in multiple with existing locomotives.”

That comes across as more of a “following the crowd” exercise, with no claim to having pioneered the system. It could also be interpreted as recognition that by then it was too late to change, even were such technically desirable.

Be that as it may, the 8-position remote control, which could be obtained using three binary actuators and so three control wires, probably appealed as a reasonable trade-off between functionality and complexity, and was found elsewhere in the world at about the same time.

In some respects, Woodward may have been more of a follower than an initiator. Early locomotive applications of the Woodward governors, including the SI and UG8 models, had speed control units that were external to the governors themselves, and so could be configured as the locomotive builder required. Load control pilot valves and floating levers, where used, were also external. Both EMD and GE had such speed control devices, of the electropneumatic type, although I have yet to find diagrams of their internal workings. A GE device of that type was used on the small Export Universal models fitted with Caterpillar engines, which in those applications had Caterpillar governors.

The change to internal speed control, and an internal load control pilot valve, came with the Woodward “New SI” model circa 1945, which I think may have made its debut on the EMD F3 (although I am not sure). This could be fitted with either electric-hydraulic or pneumatic-hydraulic speed control. The electric-hydraulic version could provide up to 15 engine speeds, using four speed control solenoids. However, the modal speed configuration was 8 evenly spaced speeds, also using the four solenoids, in the same pattern as has been established for the existing external speed controllers used by EMD and GE. To do this, the fourth, or D solenoid did double-duty as both a speed decrement solenoid and a shutdown solenoid. This speed control mechanism was described in patent US2496284 of 1950 February 07, filed 1945 May 03. The same speed control options were carried over to the ubiquitous Woodward PG governor of the late 1940s. I don’t know if there were any Woodward governor applications that used all 15 speeds, but there were some (non-US builders) examples that used 14, and also 10 and 6.

(1) Trains Magazine, 1968 December, p.44ff: “Lash ‘em Up – How to Mate Miscellaneous Makes and Models”, by Jerry Pinkepank.

(2) AIEE paper 47-37, 1947 January: “Developments in Diesel-Electric Traction-Generator Excitation Control Systems”, by C.A. Brancke and G.M. Adams.

Cheers,

18

Hey, thanks.

19

It was Herman Lemp at GE that developed the control system for GE’s early gas-electrics that was eventually used in diesel-electric:

https://www.asme.org/wwwasmeorg/media/resourcefiles/aboutasme/who%20we%20are/engineering%20history/landmarks/229-great-northern-2313-montana-western-31-gas.pdf

Frank Sprauge invented MU, dynamic braking, axle hung motors, and more for the rail industry:

https://lemelson.mit.edu/resources/frank-sprague

20

The diesel MU case probably deserves an in-depth historical and technical treatment by someone in or with close connections to the industry. As an outside observer I still have more questions than answers after several decades of looking at it.

As well as the central issues of origins and the steps towards a common standard, some other aspects worthy of consideration are:

AAR involvement in what was originally probably a locomotive builder matter.

Air brake compatibility issues (resolved in principle with the arrival of the 26L brake, in particular with its universal version.)

Dynamic braking – EMD field loop vs. GE potential wire – somewhat resolved with dual systems in the mid-1950s, probably led by railroad initiatives more than the locomotive builders, then finally addressed by EMD’s adoption of potential wire control in 1961, with retrofits available for older units. Incidentally, this was never a problem in export markets, as EMD adopted potential wire control for export models from the start. There compatibility did not seem to have been the primary driver; rather the field loop control was found to be functionally less suitable for the export models.

The inclusion of supplementary functions, such as the humping control, which – in some export applications anyway, where low adhesive weight-to-power output ratios obtained - was also used to obtain finely graduated control during starting and initial acceleration.

The various engine governors, engine speed controls and load control systems that were/are used.

The “other” systems that were abandoned as the 8-notch system became the modal type and then the standard. These included the Baldwin pneumatic throttle, the Fairbanks-Morse pneumatic throttle (different to the Baldwin), and the Alco-GE three-solenoid, eight-speed control used on early switchers. It may also be noted that the GE 70-tonner, when MU equipped, had a four solenoid, seven-speed control. Some export derivatives of the 70-tonner had pneumatic seven-speed control, as I think did the US Gypsum 54-ton model.

The situations where the standard system was interfaced with control/MU systems that were somewhat different or quite different. Some examples:

The Milwaukee “Wylie Throttle” that allowed leading DC electrics to control trailing diesel-electrics. Good information on this is available.

The UP system that allowed leading GTELs to control trailing diesel-electrics. There seems to be no detailed information available as to how this was done.

The EMD system used on the FL9 that allowed 8-notch throttle handle control of the 28-step DC electric side. Reasonable information on this is available.

The GE 16-notch system. Only partial information seems to be available.

The SP diesel-hydraulic case. Finding the details is a work-in-progress, see: Krauss-Maffei Diesel Hydraulic Locomotives - Trains Magazine - Trains News Wire, Railroad News, Railroad Industry News, Web Cams, and Forms.

There were some export situations of this nature, as well. Two examples: circa 1965, EMD developed for New Zealand Railways a two-way interface between the AAR control and the English Electric 110-volt, 10-notch protocol. And in the early 1970s, for Queensland Railways Australia, Locotrol developed a one-way interface from AAR to the English Electric 110-volt, pneumatic protocol that allowed Locotrol receiver cars to be coupled to either Clyde-GM (AAR) or English Electric mid-train units.

Returning to AAR involvement, in the Trains 1968 December article, Pinkepank made a couple of observations. Firstly: “By far the most prevalent jumper is the 27-wire type first standardized by GM in the 1940’s. The 27-point receptacle succeeded the 17-point jumper originally used for FT units and the 16-point jumper still used by some roads for E units. It is now the Association of American Railroads recommended standard, but since locomotives are not interchange equipment, the AAR standard is not binding.”

And secondly: *“*The AAR has tried for the past 12 years to settle on a standard 27-point receptacle for adoption by all railroads, but the recommended standard has been changed so often that any road which attempted to keep up with it would have spent a fortune by now in electrician man-hours.”

From that we may deduce that the AAR had been involved at least since 1956, and that by 1968 it had standardized the on the type of jumper connection (27-pin), but not the pinout sequence thereof. Presumably that came later.

Apparently, the applicable AAR standard today is S-512, although I have not yet found a copy. But I have found APTA (American Public Transportation Association) RP-E-019-99, Recommended Practice for 27-Point Control and Communication Trainlines for Locomotives and Locomotive-Hauled Equipment. This was edited 2004 March 22; I do not know if it is the latest issue.

This shows four cases for the 27-point connector:

System for Diesel-Electric Locomotives (black colour-coded receptacle) [presumably the same as the AAR standard]

MU System for Cab Car Compatible to Diesel-Electric Locomotive (black colour-coded receptacle)

MU System for Electric Locomotives (white colour-coded receptacle)

MU System for Electric Locomotive Equipped for Diesel Logic Cab Car Control (black colour-coded receptacle)

The use of diesel logic for electric locomotive control effectively goes back to the FL9, but I imagine that it was much easier to do once suitable electronics became available, to the extent that it was more-or-less routine. The description of the available control systems for the EMD GM6C electric locomotive (Railway Age, 1975 May 12, p.10) suggest this: *“*Availability of five different types of throttle control, including the typical constant-horsepower diesel-electric type with eight throttle steps (this to facilitate m-u operation with diesels) ; constant-tractive effort controls which result in the throttle’s controlling the actual tractive effort regardless of speed: and various combinations of the diesel-electric type and the constant-tractive-effort type, whatever best suits the railroad’s train-handling. ”

Cheers,

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