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Locomotive MU systems

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Locomotive MU systems
Posted by Enzoamps on Tuesday, January 18, 2022 5:07 AM

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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Posted by Overmod on Tuesday, January 18, 2022 11:45 AM

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.

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Posted by blue streak 1 on Thursday, January 20, 2022 1:16 PM

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.

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Posted by Electroliner 1935 on Thursday, January 20, 2022 5:25 PM

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? 

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Posted by BaltACD on Thursday, January 20, 2022 5:52 PM

Electroliner 1935
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? 

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!

              

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Posted by Erik_Mag on Friday, January 21, 2022 12:42 AM

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

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Posted by Overmod on Friday, January 21, 2022 5:31 AM

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

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... Whistling

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.

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Posted by Notch 8 on Friday, January 21, 2022 8:24 PM
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
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Posted by Shadow the Cats owner on Friday, January 21, 2022 11:10 PM

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.  

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Posted by jeffhergert on Saturday, January 22, 2022 10:33 PM

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  

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Posted by Overmod on Saturday, January 22, 2022 11:27 PM

Shadow the Cats owner
The airbrake one is simplicity itself.  If there is no air pressure then the emergency brakes are automatically applied.

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...

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Posted by SD70Dude on Monday, January 24, 2022 1:52 PM

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.

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Posted by oltmannd on Tuesday, January 25, 2022 8:02 AM

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

 

-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/

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Posted by oltmannd on Tuesday, January 25, 2022 8:03 AM

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.

 

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/

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Posted by jeffhergert on Tuesday, January 25, 2022 2:45 PM

SD70Dude

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. 

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    

 

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Posted by blue streak 1 on Saturday, January 29, 2022 1:02 PM

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>?

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