MU Operating

[Anonymous]

I'm sure there's information galore out there concerning operating multiple diesel units.

When a train is operating with multiple locomotives, are all of the MU hoses connected between the lead and secondary (and so on...) locomotives?

What functions are controlled on the secondary locomotives? I'm sure that speed control of the prime mover is foremost, but what other functions? Do railroads use the secondary locomotive's prime mover to generate electricity for the lead locomotives motors, or is that strictly for the secondary locomotive's motors?

I've got probably a million questions, but since I can't climb into the cab to ask the crews......besides, here I know I'll get a wealth of information from you.

Thanks!

[jchnhtfd]

I'm sure some of the old heads will get on this in detail, Joe, but very quickly: yes, all the hoses or cables are connected. The trailing locomotives are controlled by the engineer in the lead locomotive, through the cables, and almost all of their controls are active, just remoted. In newer set-ups, all or most of the various alarms are remoted back to the lead engine. The only thing which is slightly different is the air brake setup on the trailing units, which is altered by the brake valve on the trailing unit so that the lead unit can control both the train and independent air...

[CShaveRR]

Actually, you have a duplicate set of hoses on each side of the coupler, and only one of those sets needs be connected. So you have those three or four hoses, one standard M.U. cable, and the train line to connect, and you're all set.
It's probably more standardized now than it was even a few years ago. CNW used to have an electric gong instead of the standard bell, and that was trainlined...ring the gong in the lead unit and the whole lashup would sound off. But if you tried ringing the gong with a foreign unit in the consist (Chessie units are the ones I remember), the results--though I can't remember exactly what happened--were disastrous!

[Anonymous]

You also have to walk through the consist and set-up each unit appropriately. Your choices are:

trailing
leading, short-hood forward
leading, long-hood forward
isolated

Back in the dark ages of field-loop dynamic braking, you had to set that up, too. But I haven't seen that in over 30 years.

Units can not supply electricity for traction to each other except in a few specific instances where they are so wired. "Slug" units are units with traction motors but no prime mover, and take their electricity from a mother unit via heavy cables.

Everything you need to make the trailing unit do work is available from the lead unit: power, dynamic braking, sanding.

[wabash1]

The way you set up a lash of engines to be mu' ed is simple enough. first thing is take the chains from each unit and hook them up. ( these are the chains on the walk way between loco so you wont fall) then you go down to the dirty part between engines first thing i do is hook up the mu cable.( this is also known as the train line) then i will reach down and get the brake hose ( this is what most call the train line) and hook that up. then there are 3 little hoses that need hooking up. the inside one is the main resevoir hose ( and as a engineer i cant remeber the names i just do it. and know what they do) the next one i think is call act ( actuating hose for applying the engine brakes only) and then the A&P hose ( apply and release) this is for bailing the engine brakes when only using the automatic brake . the sand hose is no longer used it is done thru the mu cable electicly. after all these are hooked up and cut in you go into the cab set the unit up in trail and auto brake cut out. flip all stand switches to open. ( this is to make sure we can kill the consist from lead unit otherwise they would just keep running no matter what) and then we would set the headlight switch to desiered position. if this was a middle unit turn it to single or itermidate. of it was the rear unit turn it to long hood or short hood trail ( ge units only) or controlled from other unit coupled at either end ( emd only ) if it is a lead unit it would be long hood lead or short hood lead ( ge units only ) or it would say contolling unit couple at long hood or controlling unit couple at short hood end ( emd) this set up is only for headlight operation. and is not nessesary to do if you dont care if you have headlights on rear unit. then you go back to the head end and do a brake test independant and automatic. with each of there functions. this is it. a load test is optional and is done in differant ways i wont get into.

Now the way they operate is done by the lead unit what ever the lead unit is doing the rear units will do. No matter what the conditions are. if i have 7 units and lets say the 1st 5th and 7th units are good engines the rest are dead in tow. as long as the jumper cable is hooked up the signal will make it back to the 7th unit and will do what the lead unit is doing. each loco generates its own power to operate . the engine trailing are fully functional engines only controlled from another unit everything works just like if someone was on it operating it.

I hope i answered your questions.

[Mookie]

clear up a point for me. If you chain or rope tow a car, you can put the car in neutral and don't have to turn it on (at least this was back a few years on the older cars) If you have 7 engines, are all of them running even if 3 of them are dead in tow? For simplification, do they run in neutral, so they aren't "working" with the others? ( I figure they have to be "on" since the power has to run through them to the others.)

[ValleyX]

No, units do not have to be running, the power is transmitted through them via the MU cable and go on to the following units in the consist.

On Norfolk Southern, rules require that the independent be set up so that it will operate only on the three leading units when any one of those units is a six axle. The independent is not to work on any trailing units beyond those three. Of course, they didn't really bother to tell us how to make this work, only to not do it, and it's sometimes a challenge to get them set up right.

[zardoz]

The following refers only to SD40-2 and earlier CNW locos.

Mookie, et.al.

The CNW installed a "power saver" switch on many of it's pre-1990 locos. What this switch did was allow the locomotive to remain on-line (thereby preserving wheel-slip and other alarm indications), but the loco remained in the first-notch position at all times.

When a loco is "isolated", it is taken out of the electrical loop (although the mu signals pass thru), and no alarms will sound in the lead unit. So the engineer would have no idea if the wheels locked up, fell off, or the engine blew up.

"Dead-in-tow" means the unit is shut down completely. Isolated means the unit is running, but not functioning in any way that affects operations.

[daveklepper]

don't use the analogy with a towed car having its transmission in neutral. because these are diesel ELECTRICS. Each diesel electric is a mineature power plant with controls and electric motors added. Since the transmission between diesel and wheels is electric, if a particular unit is either isolated or cold, there won't be any current reaching the motors, whether the diesel is running in idle (isolated) or cold. Just the pass through electric control signals in the control cables (but not electric power for the motors in these cables) and the variations in air pressure in the brake trainline. Dave

[jchnhtfd]

Just to add to the confusion -- and perhaps a bit of clarification as well? -- there are four ways a locomotive in tow can be configured: running, 'power saver', isolated, and dead in tow. If it is running, it is going to be following the lead of the lead engine in all respects, and will contribute its share to pulling the train, braking, and whatever. If it is in power saver, it won't be helping much, but all the alarms will be turned on. It is isolated, the prime mover is running -- idling -- but other than that it is just a large heavy box car. It is is dead in tow, the prime mover isn't running and it is just a large heavy box car. The MU cables are run (usually!) between all the units, so that any unit which is running or in power saver can talk to the lead engine. That help any?

[Mookie]

QUOTE: Originally posted by daveklepper

don't use the analogy with a towed car having its transmission in neutral. because these are diesel ELECTRICS. Each diesel electric is a mineature power plant with controls and electric motors added. Since the transmission between diesel and wheels is electric, if a particular unit is either isolated or cold, there won't be any current reaching the motors, whether the diesel is running in idle (isolated) or cold. Just the pass through electric control signals in the control cables (but not electric power for the motors in these cables) and the variations in air pressure in the brake trainline. Dave

Yes sir - I won't do that again...

I have read this 4 times and still not sure what it says - but I will go at it from a different angle. Are all diesel locomotives diesel electrics? I am going to assume that they are, because of the ? traction motors?

After that - you lost me.

Our imaginary set-up of 7 engines with 3 dead in tow - the power will pass thru them, but not reach the motors in the electrical parts, ie traction motors or control signals. They are dead in tow and have no motors running. They are isolated and have some power, but they stay in run 1? Am I even close?

[dharmon]

I know it rare for me to actually post on a train topic...but I was actually reading about this last night....please correct me if I'm wrong...

As I understand it, some first generation deisels could not be MU'd. Baldwin Sharknoses apparently were used as helpers alot, but had incompatible MU systems with EMDs, so had to be used in ABA sets alone. I imagine that there were other non compatible units..

I also read that some railroads run the lowest HP loco as the lead of a consist to prevent overloading it...the example I saw was an F3 leading a F7 then a GP18. If either the F7 or GP was master it could overload the F3.......is this still done?

[Mookie]

QUOTE: Originally posted by jchnhtfd

Just to add to the confusion -- and perhaps a bit of clarification as well? -- there are four ways a locomotive in tow can be configured: running, 'power saver', isolated, and dead in tow. If it is running, it is going to be following the lead of the lead engine in all respects, and will contribute its share to pulling the train, braking, and whatever. If it is in power saver, it won't be helping much, but all the alarms will be turned on. It is isolated, the prime mover is running -- idling -- but other than that it is just a large heavy box car. It is is dead in tow, the prime mover isn't running and it is just a large heavy box car. The MU cables are run (usually!) between all the units, so that any unit which is running or in power saver can talk to the lead engine. That help any?

Yes Jamie - that is great - makes a whole lot of sense, now!

Thank you!

[kenneo]

Mookie

---- your 7 units with 4 live and 3 otherwise. If the unit is broken and the motor won't run, it goes DIT (Dead-In-Tow).

If for any one of several reasons, the unit is operable but must (or should) not be used for power, it is "isolated", all of the controlls are hooked up as described above, but the diesel motor simply idles and generates no electricity for the traction motors.

I put "Isolated" in quotes because it can mean any one of several setups also described above - such as PowerSaver. Since and engine at idle burns fuel and does no productive work, there must be a reason that the penny pinching railroad would do such a numbskul thing, and that reason is - with the engine running the unit provides wheel slip protection. About the only thing that is worse than flat wheels on a locomotive is a derailed locomotive.

[dehusman]

You leave the engine running to provide wheel slip protection and in cold weather to keep it from freezing up. When the temperature is below freezing and you shut down the locomotive completely, you have to drain it to keep it from freezing. Once you drain it, you can't start it until you fill it back up with water. So in cold weather unless the unit is mechaincally bad, you will leave it running when its being moved as surplus.
The really numbskull thing would be to shut it down and not drain it, causing freeze damage to the engine.

Dave H.

[Mookie]

Thanks guys -

[Anonymous]

QUOTE: Originally posted by dehusman

The really numbskull thing would be to shut it down and not drain it, causing freeze damage to the engine.

Dave H.

I saw a 16-645 come over Donner summit in Jan. and the only thing holding the engine together were the carbody doors.

[daveklepper]

Nearly all diesel locomotives on North American railroads are diesel electrics. The Kraus Maffai (spelling?) diesel mechanical, which were supposedly built to mu with USA diesel electrics but seldom did, were exceptions 9didn't last long) and so are some small industrial switch engines that don't have any mu capability. The Budd RDC and the new Colorado Railcar are also diesel mechanicals and can mu with like equpment only. For these few exceptions only, the analogies with an automobile have some validity. Don't ask me how they arranged to have the Kraus Maffai mu with diesel electrics, the complexity of the control circuits to do that would be way beyond my pressent understanding of normal diesel electric control circuits which are familiar to me and which are basically similar and compatible for EMD, Alco, Fairbanks Morse, GE, and most Baldwins, allowing all these locomotives to lashed up together and pretty much share the load properly. Even then, any engineer would probably agree that best performance is always obtained with all power being similar because of different characteristcs: power/weight ratio and thus factor of adhesion, nature of wheel slip protection, throttle response time and generator loading time, resistance of armatures and field coils and back-emf characteristics of the motors, short time permissable overload characteristcs, and then all this over again for dynamic brakes and whether the locomotive has them or not! Oh yes, transition speeds at various degrees of load, almost forgot that! (Transition: motors connected in series and then in series parallel or even to full parallel, to help the generator operate at high efficiency at different track speeds, adding field shunting for maximum speed.) Dave Klepper

[wabash1]

QUOTE: Originally posted by ValleyX

No, units do not have to be running, the power is transmitted through them via the MU cable and go on to the following units in the consist.

On Norfolk Southern, rules require that the independent be set up so that it will operate only on the three leading units when any one of those units is a six axle. The independent is not to work on any trailing units beyond those three. Of course, they didn't really bother to tell us how to make this work, only to not do it, and it's sometimes a challenge to get them set up right.

this is not totally true. the independant brake has to operate on all engines the only exception on this is when the engine is a noncomplying engine. and then it deals with the number of axels and type of wheel if i remeber correctly. the way you cut the engine out is to cut out the brake on the trucks ( look close there is a axel c/o **** on each engine for this and only for that truck ) but dont forget to cut this back in. just because a engine is dead in tow doesnt make it non complying.

Mookie a engine that is isolated is just that isolated it running but doing nothing. the brakes will work but that is it. it wont be in notch 1 it is idling and providing air for the train. if i have your 7 engines ( this may get complicated just bare with me) and for simplicity lets just pair them up ..

1st engine - dash 9 refered to as engine 1
2nd - dash 9
3rd- dash 9
4th- sd40
5th sd40
6th- sd70
7th-sd60

all engines are 6 axel units. but due to type of wheel engine 1,2,3,6,7 are high adheshion units and are considered as being equivalent to 8 axel ( dont try and figure it out just take my word for it. but if you must know on high adhesion axels they are considered 1 1/3 per axel so 1 1/3 x 6 = 8 ) now on trains you are not allowed to have more than 24 powered axels on line( ns anyways) and no more than 18 axels in dynamic ( bulk comodity trains being 30 power and 24 dynamic) so with are power lash up the 1st 4th 7th engines are working engines no problems this gives us 22 axels of power and dynamic cut out on the 4th is 16 dynamic. ( 1st engine equivilant to 8 and also the 7th is 8 but a sd 40 is not high adhesion so it is a standard 6axel so regular math 8+8+6 =22) now why not the other engines engne 2 is fra dead cant be used just idling going for the ride. engine 3 has a crank case overpressure problem dead and drained. engine 5 fra dead engine 6 trips ground relay and is dead in tow. all engines are in complyance except for number3.

now with the jumpers connected between all units the rear unit #7 knows what the engineer wants it to do if i get a notch it gets a notch. all other units know this to but being they are isolated they dont care they just going for the ride. the usable engines dont haft to be together to use ( all three together) they can be seperated by others but must be jumpered together. another anology that might help in how a isolated engine works would be a window fan the blade being the wheel spin it with your hand this is how it is going down the track isolated just spinning free, but turn it on ( put it on line as we say) and it provides traction to move the train.

I sure hope this helped....and didnt confuse you more.

[Anonymous]

Holy Crap! And I thought mu just meant "multiple unit".

Wabash, the amount of technical information you have about runnin trains is utterly amazing! [bow][bow]

I have learned more in this one short thread about the operations I see and take for granted almost every day, it gives me a great deal more understanding and appreciation for what you all do!! And that's just getting the damn things hooked together!!!

Thanks for the insight.

Jeff

[tree68]

Wabash - Great explanation. Learned something useful today!

[WDGF]

What causes wheel slip on an isolated unit? Brakes dragging? Friction in the traction motors?

[Anonymous]

HOW DOES THE TRAILING UNIT KNOW WHICH WAY IS FORWARD? IS THERE A CONTROL TO SET TO DENOTE WHICH END OF THE ENGINE IS THE FRONT FOR THE PARTICULAR LASH UP?

Dave

[kenneo]

QUOTE: Originally posted by daveklepper

Nearly all diesel locomotives on North American railroads are diesel electrics. The Kraus Maffai (spelling?) diesel mechanical, which were supposedly built to mu with USA diesel electrics but seldom did, Dave Klepper

KM's were Diesel-Hydrolics and MUed quite well with US units. Standard procedure was a KM and an F7 to operate as a unit.

[kenneo]

QUOTE: Originally posted by bristolian

HOW DOES THE TRAILING UNIT KNOW WHICH WAY IS FORWARD? IS THERE A CONTROL TO SET TO DENOTE WHICH END OF THE ENGINE IS THE FRONT FOR THE PARTICULAR LASH UP?

Dave

Yes, Sir, there is a control - it's called the headlight switch. Also, for intermediate units there is the polarity of the reverser circuit.

[kenneo]

QUOTE: Originally posted by WDGF

What causes wheel slip on an isolated unit? Brakes dragging? Friction in the traction motors?

Wheel slip comes in several varieties. You have named two of them and they are the ones responsible for wheel slip for units DIC.

[Anonymous]

What is the "polarity of the reverser ciricuit" for we railfans who can tell you the difference between a K-4 and K-3 from 2 miles away but couldn't tell a PA from a DASH-9 if it were right in front of us?

-Daniel

[Anonymous]

Wheel slip in an isolated unit would almost always be a very bad thing.

Sticking brakes: ordinarily, unless the units are running light in a yard, the locomotive air-brakes are not used (they're "bailed off" in an automatic reduction), so would have no opportunity to stick. Sticking brakes on a car are a result of no release or an overcharge, and I don't know how you'd get either condition on a locomotive without really doing something wrong.

Traction motors: that's not friction per se causing wheel slip, it's a seized motor bearing or locked pinion. Either is very bad and will lead to a derailment if ignored for not very long.

Most common of all: a set hand-brake that was not released. Yes, this happens. A unit picked up en route or swapped between consists en route may very likely have had its hand-brake set. If it's not released, that axle will drag and since it is not slipping, per se, may not show as a wheel slip. I saw $35,000 damage done to an AC4400CW in about 30 minutes one night because a crew forgot to release a hand-brake after a unit swap.

Traction motor leads connected backwards. This happens too, but normally it's discovered the first time the locomotive is moved under power in the engine terminal. It may also not show up as a wheel slip. If it does it for very long the wheelset will develop an outside flange.

An outside flange will probably cause a derailment at the first switch it comes to. Since the train is probably moving at a good clip to have ground the wheel this way, and the locomotive is probably close to the head of the train, an enormous pile-up will ensue. I can recall one of these, too, on BN in Colorado Springs, Colo.

[M636C]

I am tempted to relate an anecdote about an electric locomotive assembled by the New South Wales Railways in the early 1950s. It was built to train drivers before the first "production" locomotives ordered from England arrived. It was standard gauge, 1500 volts overhead, 2700HP and weighed 108 tons on six motored axles. It was initially numbered 4501, and later 7100.

To get it out quickly, the control equipment from three commuter cars (each normally with two motors) was used. So effectively, this unit ended up as three two motor units in multiple unit, complete to having three line breakers mounted on the roof.

The operators reported that it was very sluggish after return from maintenance, so a couple of junior engineers were sent out to the electric car sheds where it was kept , early on a cold and wet morning.

One of the engineers was standing beside the unit as it was started up and moved off for some tests. To his amazement, the wheels slipped, four rotating in one direction and two in the other! Fairly quickly, he had the unit stopped, the pantographs dropped, and he went in and swapped over the reverser switch on the set of control equipment that was set the wrong way, and they returned happily to their warm office.

(Swapped traction motor cables would have the same effect)

Peter

[edblysard]

Heres another odd way to put nice flat spots on a locomotives wheels.

Last week, we had a BNSF crew drag a train into our receiving yard, but, just as the last car cleared the south switch on the main, they hit the hours of service law.
They had one of their taxis waiting for them on the north end, so they just tied the train down, motors and all, and left.

Later that afternoon, we were sent to drag the train out, and switch it.

Everyone, yardmaster, train master and us, assumed the BN crew had cut the motors away before tieing them down, which is standard practice and common courtesy.

Our car dept had closed the angle **** at the motors, bled off the air, and then failed to mention to anyone the fact that the train was still intact, locomotives and all.

So, we get against the south end of the train, and start pulling.

First 150, 200 yards, no sweat, than suddenly, the train got very, very heavy, to the point we started to slip the wheels on our 3000 hp mu.

First guess was that the carmen had left the hand brakes set on the north end, but that wouldnt create so much drag that we would stall.

So I walked on down, and surprise, we have two SD40-2s on the rear of the cut, brakes all nice and set.

All the BN crew did was isloate the motors, they didnt even bother to set the handbrakes.
The engineer had used the train brake to stop the train, hadnt even set the independent.

So, when the locomotives started to move, the wheel rev counter started also, and then the alerter/deadman switch did what it was designed to do, after the required time with no control surface being moved, it set the locomotives brakes.

Had we had another 1500hp on our end, we would have drug them all the way through the yard with the wheels locked.

As it was, I got to ride them out, and every time the alerter went off, I would either bail off the independent, or rev the motor up, to keep the deadman circut from doing it's thing again.

Nice ride back into the yard though, beats the heck out of hanging on the side of a hopper for a mile or two...
And I got to have a little fun with my engineer, every once in a while, I would get a light reduction, just enough to bunch the slack up, and send a little bump back to him, as a friendly reminder of how much fun it is to eat slack action.
Ed