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Mid DPUs and slack between them and the car in front of them

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Mid DPUs and slack between them and the car in front of them
Posted by Perry Babin on Tuesday, March 28, 2023 2:21 PM

How does a mid DPU always keep tight against the car in front of it if the DPU and the lead locomotive are running in the same notch/speed?

It would see that small differences in speed due to load or terrain would cause there to be repeated instances were the DPU would lose solid contact with the car in front of it.

Can you run a combination of AC and DC locomotives when using DPUs in the same train?

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Posted by timz on Tuesday, March 28, 2023 4:02 PM

You mean, is the midtrain engine always pushing the car in front of it? Sounds unlikely.

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Posted by YoHo1975 on Thursday, March 30, 2023 12:26 PM

I regularly see UP running mid train units in a GE-AC (GEVO or AC4400) + SD70M AC-DC pair. So yeah, you can do it.

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Posted by BigJim on Thursday, March 30, 2023 12:35 PM

It depends on how much power is on the head end and the amount of tonnage ahead of and behind the DPU units.

.

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Posted by BaltACD on Thursday, March 30, 2023 4:08 PM

The Engineer's primary job is to control the slack within the trains to prevent it from tearing the train apart using the tools that the Engineer is provided.  Those tools are Head End locomotives, DPU locomotives where ever they may be placed within the train and the air brakes of the train.

Manipulating those tools and getting the train from Origin to Destination over territory with various kinds of grades, both long and short, as well as degrees of curvature that can be traversed at maximum track speed one down to much slower speeds.  

The 'train' can be anything from Light Power to 18K feet in length.  

Simple Job [/sarcasm]

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Posted by Perry Babin on Friday, March 31, 2023 9:22 AM

Is it a common failure to have the coupler in front of the mid DPU to break?

I would think the slack would be hard on the couplers but I don't really see any breaking there. 

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Posted by BaltACD on Friday, March 31, 2023 1:16 PM

Perry Babin
Is it a common failure to have the coupler in front of the mid DPU to break?

I would think the slack would be hard on the couplers but I don't really see any breaking there. 

Slack moves throughout the train as it traverses the territory it operates over.  Depending upon the territory its is possible for one part of the train to be experiencing Draft forces, another part of the train to be experiencing Buff forces and a third part of the train to be adjusting between Draft and Buff forces. Think of a train climbing one side of a grade and then descending down the other side, or a train operating over multiple undulating hills and valleys within the length of the train. 

Engineers may/can control DPU power independent of the lead engine consist as they have a electronic fence that permits the DPU to be operated in a different manner than the lead consist.  At the Engineers control all engine consists on a train may operate in a sychronized manner.

 

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Posted by Perry Babin on Friday, March 31, 2023 6:44 PM

I've seen only one video (I have no access to locomotives) that had a variable control in a lead locomotive for the speed of a DPU but they seemed to say that type of control was very rare and possibly a thing of the past. 

It would seem that a constant/slight push by the DPU would be easier on the couplers but if they're not breaking, it may not be important. 

Thanks for the replies. 

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Posted by Pneudyne on Friday, April 14, 2023 5:10 PM
This book may provide the answers to your questions:
 
The Only Game in Town – The Locotrol Story, by Fergus Moffat
Ingram-Spark, La Vergne, TN, USA, 2021
ISBN 978-0-6485290-1-9
 
 
It includes charts and equations relative to the in-train placing of mid-train locomotives.  The optimum placement apparently varies situationally.  But broadly what was said was that in undulating territory, the mid-train units are paced around two thirds of the way back, so that they both push and pull, with the nodal point floating somewhat ahead of them.  On the other hand, for continuous uphill running, mid-train placement could be used, with the nodal point just ahead of the mid-train units.
 
The book as a whole is a good read, being a partly anecdotal history of Locotrol, with chapters on specific railroad applications, much attention being given to the CP case.
 
 
Cheers,
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Posted by blue streak 1 on Saturday, April 22, 2023 10:00 PM

CSX  certainly did not read the book oprating on the A&WP sub.  Here the DPU is usually on the 1st quarter of the train running Max power to maintain track speed. (50 MPH ).  Front unit anywhere from idle to whaever to maintain track speed.  Lately the few short trains with DPU on rear has rear unit doing all the work.  Dynamics rerely used except for stop signals . Unable to tell how dynamics are used.

These methods all changed to this maybe a week after NS at east palestine.  Not claiming any correlations. 

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Posted by Perry Babin on Sunday, April 23, 2023 2:20 PM

blue streak 1

CSX  certainly did no dead the book on the A&WP sub.  Here the DPU is usually on the 1st quarter of the train running Max power to maintain track speed. (50 MPH ).  Front unit anywhere from idle to whaever to maintain track speed.  

This answers a couple of questions (here and on another thread I posted). I didn't understand that the DPUs would be run at significantly higher power (notch) than the leading locomotives. 

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Posted by jeffhergert on Sunday, April 23, 2023 3:23 PM

blue streak 1

CSX  certainly did no dead the book on the A&WP sub.  Here the DPU is usually on the 1st quarter of the train running Max power to maintain track speed. (50 MPH ).  Front unit anywhere from idle to whaever to maintain track speed.  Lately the few short trains with DPU on rear has rear unit doing all the work.  Dynamics rerely used except for stop signals . Unable to tell how dynamics are used.

These methods all changed to this maybe a week after NS at east palestine.  Not claiming any correlations. 

 

The auto throttle Energy Management Systems love running the Mid and/or rear DP consists higher than the head end, making more tht.rottle adjustments on the lead consist.  Sometimes there is merit in that.  Most of the times doing that results in slack action.  Something that we are to avoid.  It comes, I believe on the part of some, that it's always better to have the slack bunched as much as possible.  Most of us believe the opposite.  It's better stretched out in most cases.

The other day I had an empty grain train, 2x1 everything on line.  (We've had instructions since about the time of the latest STB grilling to have all usable units on-line.)  EMS kicked us in the seat every few minutes, sometimes really noticeable has it waffled on the head end between power and dynamics while not changing or worse, increasing the throttle on the DP.  Didn't matter where the train was topography wise.

I told the conductor I want to spend 8 hours with the programmers and those in the glass palace that think these things are so much better.  I want to stand behind them and every few minutes grab the back of their chair and give it a hard jerk.

Upon tie up I left the comment for EMS use and said a fireman in training on his first trip, first time in the seat and without any advice from his training engineer could do a better job of handling the train than their vaunted EMS.

Jeff  

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Posted by timz on Sunday, April 23, 2023 3:31 PM

jeffhergert
... could do a better job of handling the train than their vaunted EMS.

Do they actually vaunt it? What advantage does the RR claim -- it's supposed to burn less fuel than the hamhanded engineers?

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Posted by jeffhergert on Sunday, April 23, 2023 7:35 PM

timz

 

 
jeffhergert
... could do a better job of handling the train than their vaunted EMS.

 

Do they actually vaunt it? What advantage does the RR claim -- it's supposed to burn less fuel than the hamhanded engineers?

 

 

It's the doorway to complete automation.

The EMS can do no wrong.  When it does, it's of no consequence.  My Local Chairman in preparation for an investigation for train handling violations, asked for collected data on train separations caused by EMS operation.

The railroad doesn't have any.  It's not that EMS doesn't tear trains up, it's that they only compile data on human caused incidents.  

Jeff      

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Posted by BaltACD on Sunday, April 23, 2023 8:08 PM

timz
 
jeffhergert
... could do a better job of handling the train than their vaunted EMS. 

Do they actually vaunt it? What advantage does the RR claim -- it's supposed to burn less fuel than the hamhanded engineers?

Carriers get a 'plot line' and stick with it - without regard to any conflicting data.

Most all operating divisions on a railroad have their Chief Dispatchers keep some kind of 'log' about the 'unusual activities' that happen on the particular territory over the course of a day so that Division Officials can be 'kept up to speed' about what is happening on the territory they are responsible for.  For the most part these logs are reviewed and then the official moves on to the next day.

It is amazing what data correlations can be ascertained when the data from these logs are 'mined' over time.

Curmudgeon that I was, I mined the data and then made issues of some of the repetitive happenings - that were infrequent enough to be confused as a 'freak' happenings, but weren't.  Got a number of things 'fixed' over the years.

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Posted by blue streak 1 on Saturday, April 29, 2023 11:02 PM

This post does not follow this thred exactly. 

I have to wonder if slack action is a product of the number of couplers in a train + any cushoined cars.  a 9000 foot iron ore train might have as many couplers as a 16,000 foot grain train.  Then if the RR has a loaded 15,000 foot intermodal train with just 3 and 5 packers that train might have fewer couplers than a mixed 5000 foot train.  That train would probably need DPUs espcially in mountain areas. 

The next question then becomes what is the derailment rate of IMs v. regular trains.

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Posted by BaltACD on Sunday, April 30, 2023 11:19 AM

blue streak 1
This post does not follow this thred exactly. 

I have to wonder if slack action is a product of the number of couplers in a train + any cushoined cars.  a 9000 foot iron ore train might have as many couplers as a 16,000 foot grain train.  Then if the RR has a loaded 15,000 foot intermodal train with just 3 and 5 packers that train might have fewer couplers than a mixed 5000 foot train.  That train would probably need DPUs espcially in mountain areas. 

The next question then becomes what is the derailment rate of IMs v. regular trains.

Slack action is more related to the territory over which a train operates than it is to the number of couplings that are in a train.

Most all territories that trains operate over have some level of grade - the 'flat earthers' have never really looked at the Earth - it is far from flat.  Rivers, streams and creeks all create valleys that are lower than the surrounding area - that is why rainwater drains to these waterways.  Since these waterways flow it means that there is a difference in their elevation along the course of their flow.

Rich railroads, as they built their lines attempted to smooth out these undulations; poor railroads laid their tracks on top of the ground and its every change in elevation.

Longer trains move the train over more ground undulations at the same time than do shorter trains.  The undulations create draft forces on the upgrade and buff forces on the downgrade.  A long train can be stretched across multiple peaks and valleys at the same time - controlling the slack in such trains in such territory is where the skills of the Engineer get highlighted.

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Posted by Overmod on Tuesday, May 2, 2023 9:57 AM

One of the fun 'timeless topics' in autonomous-train design has been the prospective use of ECP for modulated in-train braking of blocks or individual cars to control in-train slack beyond what simple power modulation can do.  Without short-term ability to do graduated release without respect to recharge, an attempt to do that with 'midtrain modules' might be near-suicidal in a variety of dismally predictable ways... and attempting to implement it as an overlay for TO or Leader is very, very little better.  It also presumes very good 'computer control' of small applications and releases of the car brakes, without affecting the systems that produce emergency application (which I understand cannot be released while the train is still physically moving) -- you would need a display from on-car accelerometers and strain gages for a 'human' engineer to keep track of all the little in-train forces and how to adjust them, even if there weren't dangerous lags and latencies involved.

This also presumes a high level of continuous location accuracy (including GPS integrity) and reasonably up-to-date GIS integration plus PTC 'civil'.  With any error or miscalculation potentially becoming 'written in blood'.

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