MU'd Locomotive question

[Overmod]

Former Car Maintainer

It's important to know that this thread seems to only talk about diesel electric to diesel electric, using the 27 pin multiple unit connectors. There are other forms of MU such as steam locomotive with diesel electric locomotive assist, and commuter transit electric rail cars with 100 pin train lines...

Practical control of steam locomotives (as opposed to firing control, an immensely different but 'not unrelated' subject) was demonstrated very early in the 1920s, I think spurred in part by the promised progressive introduction of mandatory automatic train control.

While proper ATS requires only centering the valve gear and optionally closing the throttle or interrupting the flow of steam to the valves, the introduction of ATC and running speed control requires most of what's needed to work an engine remotely; inherent in the automatic cutoff controls demonstrated by 1922 was the ability to adjust a power reverse proportional to back pressure, and even with 1920s technology it would not be difficult to make a proportional system that could appropriately 'repeater' the head-end throttle and reverse correctly for different types of trailing engine(s), including proper indicators for the firemen in the consist.

Control of trailing diesels is much more complicated if they use the notch system (which is digital control of engine speed and loading and only peripherally relates to steam-locomotive control.  To my knowledge only one system lends itself to easy proportional 8-notch control: Franklin type D (which makes ingenious use of wiredrawing for control of an engine with rotary cam poppet valves).

There have been a number of more or less complicated ways to MU trailing steam with diesels over the years, including on several designs of steam-turbine-electric where the effects of load regulation can be precisely repeatered in a setup with continuous throttle (like the Baldwin air throttle).  Getting a proportional load-regulator signal (or, more properly, deriving and then correcting one) poses an interesting technical exercise 'over the years' as technology robust enough to survive in a railroad environment has changed.

[CSSHEGEWISCH]

Steam to diesel control has existed only since the fantrip era began, probably with Clinchfield 1.  It is basically the addition of a diesel locomotive throttle or hostler control next to the steam locomotive throttle.  It is not so much MU as remote control of the diesel.

[Former Car Maintainer]

It's important to know that this thread seems to only talk about diesel electric to diesel electric, using the 27 pin multiple unit connectors. There are other forms of MU such as steam locomotive with diesel electric locomotive assist, and commuter transit electric rail cars with 100 pin train lines...

 

[daveklepper]

If two units are always facing forward on a specific freight operation, one explanation is that somewhere along the line there is a junction and/or crew point and from that point forward there two separate trains. Not necesarily two different lines either, one section (prelbocked) might run nonstop to the terminal point and the rear portion operate as a peddler or junk train with pick-ups and set-outs.

[ValleyX]

It might be common to leave the fuel pump and engine run buttons up on trailing units but it isn't company policy and if a road foreman shows up and goes through your power, you'd best have a good reason why you didn't take time to put them down.

The theory is that if you need to shut the power down in a hurry, pulling out on the throttle enables you to shut down all the power in the consist at once but this only works if the trailing power is set up correctly, i. e., with the control buttons down.

I've never known of a MU cable to come disconnected by itself, it's not like an airhose, it's up much higher. The only ones I've known to come disconnected is if the consist separated and if that happens, then you've got far bigger problems.

[harpwolf]

If you uncouple trailing units, you suddenly have two trains. Both in emergency, because the brake pipe got vented when they uncoupled.

[wccobb]

Haven't read much recently about gear wear. Time was when this was important, running a gear driven loco (diesel electric, shay, etc.) always in one direction wore only one side of the gear teeth. Running them in both directions wore both sides of the teeth - half as fast = @ double the milage between new gears.

[edblysard]

AJ answered your question about the way the locomotives face...it saves having to turn them around, although they work just as well, no matter which way they face.
Some railroads have aggrements with the local union that require the lead locomotive to always face forward, so MUing them rear to rear makes even more sense, either one can be used as a lead, depending on which direction you are going.
As for what happens if, by some twist of fate, the locomotives un-couple, either from each other, or the train consist, the emergency brakes apply on the entire train.
Light locomotive, with no train, all the locomotives will again go into emergency.

Ed

[arbfbe]

goatherder:

If the train comes apart between the units then the airhoses become uncoupled, the train goes into emergency and the train comes to a stop. Just the same as if the train parted between a couple of cars in the train except the safety chains between the units likely will ben the handrails outward.

Alan

[ajmiller]

QUOTE: Originally posted by BigDarrin

I have a sort of related, but newbie question. Is there a particular reason for alternating the direction that the locos are facing? I've seen various combinations and wondered if it made just as much sense to have all facing the same direction as it does to have them front back front back.

Back to your regularly scheduled program....

Well, it would make sense to have the first locomotive facing forward and the last facing backward so they have a cab on each end of the consist. That way they could more easily operate consist without having to turn any of the units. The direction of the units in the middle of the consist really wouldn't matter at all. If the consists you've seen have alternating orientations, maybe they were assembled from pairs of locomotives that were already coupled back to back. I've seen consists where all the locomotives were facing forward, and I've seen them when only the lead engine is facing forward. I'm not sure I've seen in person any main line trains where the lead engine was facing backward, but it probably happens from time to time. There aren't very many places to turn locomotives, and I guess they like to have some facing each way so that they can change direction easily.

Last April I followed a coal train from Tyrone PA to Lock Haven PA and it was lead by 3 SD40-2's. The first two were facing forward and the last one was facing backward. When the train got to Lock Haven, it stopped in the yard there and the front two locomotives decoupled and they replaced the middle locomotive with another SD40-2 that was sitting in the yard. The replacement was facing backward, so I assumed that they dropped the forward facing unit in Lock Haven to haul a small train toward Harrisburg PA. The backward facing unit would have been facing the wrong way for a move from Lock Haven to Harrisburg. There's no longer a wye in Lock Haven so a train that rates only a single locomotive would have to be facing the right way ahead of time.

[Anonymous]

I have a sort of related, but newbie question. Is there a particular reason for alternating the direction that the locos are facing? I've seen various combinations and wondered if it made just as much sense to have all facing the same direction as it does to have them front back front back.

Back to your regularly scheduled program....

[Anonymous]

ok what about if you uncouple same scenario? train stops or continues on rolling?

[edblysard]

Yes, they become real heavy boxcars..
Seriously, they already have the reverser in netural, and the throttle is in idle, so they just become dead weight...the brakes will work, but thats about it.
The headlights will not work, unless the switch on the cab wall is set for one or the other ends....

Ed

[arbfbe]

If the console switches are all set correctly the units behind the dropped MU cable will shut down. However it is common that the Engine Run and the Control & Fuel Pump switches get left in the on position on trailing units and so the locomotives just drop to idle.

[Anonymous]

Here's a question: Say that your going down the road and for some unkown reason an MU cable is disconnected somewhere in the consist, will the rest of the trailing units continue on or will they shut down into idle and nuetral?

[csxengineer98]

QUOTE: Originally posted by CHIPSTRAINS

AFTER READING EVERYONES EXPLANATION OF MU'ING, I HAVE A HEADACHE AND AM GOING TO LAY DOWN. WHEN I GET UP AND GOING AGAIN, I WILL PROBABLY ACCEPT THE SWITCH ON THE BACK WALL EXPLANATION. AM I RIGHT?? C'MON GUYS, DISPENSE WITH ALL THE TECHNICAL MUMBO-JUMBO, WE'RE RAILFANS, NOT ELECTRICAL-ENGINERING STUDENTS. "CHIP"

listen to the ones that work with the eqipment..such as valleyx and myself..we are railroaders.... the explinations about the "switch" have been explained by valleyx and myself... a few people are trying to over explain it... its not hard.... making 4 units act as 1 is a matter of pluggin in the jumper cable and setting up the air brakes..... its not rocket science...its railroad 101.....
csx engineer

[daveklepper]

Read all the posts again. If you still don't get it write me at

[e-mail]

and I will scan a diagram for you and send it as an attachment to the reply to your contact.

[ValleyX]

No, the switch on the back wall is strictly for the headlight control, allowing the engineer to control the headlight on the leading as well as the trailing engine. The MU cable, sometimes referred to in some parts of the railroad world as a "jumper cable", connects the locomotives electrically, permitting the engineer to control the direction and power source from the controlling engine. The MU2A valve permits the engineer to control the brakes (other than dynamic) on the consist from the lead engine.

[CHIPSTRAINS]

AFTER READING EVERYONES EXPLANATION OF MU'ING, I HAVE A HEADACHE AND AM GOING TO LAY DOWN. WHEN I GET UP AND GOING AGAIN, I WILL PROBABLY ACCEPT THE SWITCH ON THE BACK WALL EXPLANATION. AM I RIGHT?? C'MON GUYS, DISPENSE WITH ALL THE TECHNICAL MUMBO-JUMBO, WE'RE RAILFANS, NOT ELECTRICAL-ENGINERING STUDENTS. "CHIP"

[BigJim]

Boy am I glad that is over with. Reading some of the early posts made me want to scream.

[wccobb]

They was a persistant rumor that the guys at ALCO didn't figure out the "pin #8 & pin #9" automatic directional reversing on the early SR-1s. They HAD to be coupled "elephant style" to go in the same direction.

[Randy Stahl]

QUOTE: Originally posted by zardoz

QUOTE: Originally posted by Randy Stahl

QUOTE: Originally posted by arbfbe

Quite simply, all units in the consist will move in the direction the reverser in the lead unit is placed. Trailing units behave as if the lead reverser was installed in that unit. There are NO switches specifying the trailing unit orientation to the lead unit EXCEPT for RCU consists.

Most of the answers posted here are just absolutely wrong.

Perhaps I can simplify it a bit, seems like alot of people are over complicating things. A locomotive isn't that smart, it is A very simple machine. Each locomotive has a RER (reverse) relay and an FOR (forward) relay. If you have a single unit and you throw the reverse handle in forward, the FOR relay will energize and pick up. When this relay picks up the reversers will move to the correct position, the power contactors will pickup,and the locomotive will begin to load. At the same time a parellell wire . 8T will also become positve 74 VDC. remember that the pinouts are different from front to rear. Pin 9 will be positve on the front, pin 8 on the rear. You will see that no matter which direction the locomotives are facing the correct relay will pickup .
Randy

Unless, of course, you happen to be using a 27-point jumper that had got pinched somewhere and had a few wired crunched together; then one unit might want to go a different direction than the other unit(s). Quite exciting when it happens. Sometimes the units want to seperate, sometimes the want to collide.

Yea, lost a good friend at Western Ave. that way. Myself, I have seen the MU recepticle cover come apart and short out pins. Really scary when locomotives get a mind of thier own.
Randy

[zardoz]

QUOTE: Originally posted by Randy Stahl

QUOTE: Originally posted by arbfbe

Quite simply, all units in the consist will move in the direction the reverser in the lead unit is placed. Trailing units behave as if the lead reverser was installed in that unit. There are NO switches specifying the trailing unit orientation to the lead unit EXCEPT for RCU consists.

Most of the answers posted here are just absolutely wrong.

Perhaps I can simplify it a bit, seems like alot of people are over complicating things. A locomotive isn't that smart, it is A very simple machine. Each locomotive has a RER (reverse) relay and an FOR (forward) relay. If you have a single unit and you throw the reverse handle in forward, the FOR relay will energize and pick up. When this relay picks up the reversers will move to the correct position, the power contactors will pickup,and the locomotive will begin to load. At the same time a parellell wire . 8T will also become positve 74 VDC. remember that the pinouts are different from front to rear. Pin 9 will be positve on the front, pin 8 on the rear. You will see that no matter which direction the locomotives are facing the correct relay will pickup .
Randy

Unless, of course, you happen to be using a 27-point jumper that had got pinched somewhere and had a few wired crunched together; then one unit might want to go a different direction than the other unit(s). Quite exciting when it happens. Sometimes the units want to seperate, sometimes the want to collide.

[chad thomas]

Didn't I say that already ???[:D][8D][:D][8D][:D][8D][;)]

[daveklepper]

Again, this works because pin 9 on the front is pin 8 on the rear and visa versa.

[Anonymous]

On my MRC throttle, I pu***he switch to Rev and the engines move backwards. Regardless of the way they are facing in the consist or whether they are Atlas, Athearn, or Kato.

With the AHM's its different. But then again, they are european.

[Randy Stahl]

QUOTE: Originally posted by arbfbe

Quite simply, all units in the consist will move in the direction the reverser in the lead unit is placed. Trailing units behave as if the lead reverser was installed in that unit. There are NO switches specifying the trailing unit orientation to the lead unit EXCEPT for RCU consists.

Most of the answers posted here are just absolutely wrong.

Perhaps I can simplify it a bit, seems like alot of people are over complicating things. A locomotive isn't that smart, it is A very simple machine. Each locomotive has a RER (reverse) relay and an FOR (forward) relay. If you have a single unit and you throw the reverse handle in forward, the FOR relay will energize and pick up. When this relay picks up the reversers will move to the correct position, the power contactors will pickup,and the locomotive will begin to load. At the same time a parellell wire . 8T will also become positve 74 VDC. remember that the pinouts are different from front to rear. Pin 9 will be positve on the front, pin 8 on the rear. You will see that no matter which direction the locomotives are facing the correct relay will pickup .
Randy

[arbfbe]

Quite simply, all units in the consist will move in the direction the reverser in the lead unit is placed. Trailing units behave as if the lead reverser was installed in that unit. There are NO switches specifying the trailing unit orientation to the lead unit EXCEPT for RCU consists.

Most of the answers posted here are just absolutely wrong.

[K. P. Harrier]

For simplification’s sake, don’t MU’ed units sense WHICH WAY a direct current signal initially travels through a unit, and, irregardless of which way any unit is physically facing, will automatically move in directional unison with the other units in the consist? Wouldn’t the only way to get a trailing unit to work opposite other units would be to have a 100-foot MU cable and connect it to the opposite far end of a unit?