Overmod 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.
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.
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.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
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
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.
Greetings from Alberta
-an Articulate Malcontent
Shadow the Cats ownerThe airbrake one is simplicity itself. If there is no air pressure then the emergency brakes are automatically applied.
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
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.
Erik_MagSome of the really old-time diesels had pneumatic throttles.
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.
Some of the really old-time diesels had pneumatic throttles.
Electroliner 1935Since 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?
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.
Never too old to have a happy childhood!
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?
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.
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.
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