AKA dragging equipment detectors. Quite possibly what alerted this crew. How many times are you going to reinvent the wheel?
tdmidgetAKA dragging equipment detectors. Quite possibly what alerted this crew. How many times are you going to reinvent the wheel?
If dragging equipment detectors alerted this crew, they did a piss-poor inadequate job of it. Are you suggesting that dragging equipment detectors of the usual types be placed every mile, or at the entrance to every curve, so an incipient HHFT derailment will be caught before it progresses to damage and fire? And then discriminate between actual dragging equipment and broken axles or derailed trucks? That technology isn't going to work well enough.
As Euclid indicates, an accident like this is a 'poster child' for actual derailment detectors, probably devices mounted on individual cars that can signal promptly when problems are detected. To some extent such a device can also check or track bearing problems better than wayside IR detectors.
Personally I think any of the money Sarah wants to spend on ECP ought to be put dollar for dollar into this technology instead, until all the HHFT and PIH cars have been instrumented and the added programming (to PTC) for alerting and information exchange with the devices has been done. I'd even go so far as to state implementation of these devices is a priority over the boondoggle that "PTC" has become at this point -- it certainly offers a much more positive and direct form of 'safety' provision.
A dragging equipment detector would detect a derailment, but it is a wayside stationary detector, whereas a true derailment detector is mounted on the rolling stock. It, of course is possible that a dragging equiment detector happened to alert the crew of the CSX train if there happened to be a dragging equipment detector between Middlesettlement Rd. and Old Mt. Tabor Road.
But derailment detectors on board are hardly reinventing the wheel, as you say. A derailment sensor on each truck finds a derailment the instant it happens. A dragging equipment detector has to wait for the derailment to arrive.
Wizlish As Euclid indicates, an accident like this is a 'poster child' for actual derailment detectors, probably devices mounted on individual cars that can signal promptly when problems are detected. To some extent such a device can also check or track bearing problems better than wayside IR detectors. Personally I think any of the money Sarah wants to spend on ECP ought to be put dollar for dollar into this technology instead, until all the HHFT and PIH cars have been instrumented and the added programming (to PTC) for alerting and information exchange with the devices has been done. I'd even go so far as to state implementation of these devices is a priority over the boondoggle that "PTC" has become at this point -- it certainly offers a much more positive and direct form of 'safety' provision.
So where does this detector get its power? How does it communicate to PTC? Via the locomotive? Fairly strong radio signal required and of course additional already scarce bandwidth.
Actually this would be inferior to IR detectors as IR detectors find impending failures, this detector would find failures unless you are proposing sensors on all eight bearings. How many hot box setouts are there without a derailment? The vast majority I would bet. Even better are the acustic bearing detectors that find bearing defects long before they become impending failures.
The industry did a cost benefit on on-board detectors a few years ago and found far more problems than benefits.
BuslistThe industry did a cost benefit on on-board detectors a few years ago and found far more problems than benefits.
Likely that was before the transport of oil surged. The avoidance of disastrous derailments of oil would change the outcome of that analysis now. And the industry has a duty to run safely, even if that cuts into profits. It's part of the cost of being in business responsibly.
C&NW, CA&E, MILW, CGW and IC fan
Not to criticize in any way your professional competence as one of the better-qualified and knowledgeable contributors here -- You say this and don't provide a source, citation, or link? Don't indicate what the 'problems' were, let alone with any sort of indication why they were greater than the equally unindicated) benefits cited? Please document, and at least synopsize the detail conclusions here. A discussion can't go forward just on use of older technology and unqualified appeals to authority.
None of this is technically 'showstopping' (as yet), although I really can't describe much of the technical detail without causing NDA problems. There is at least one critical issue involving methods of wireless communication, but I understand there is European OTS (or at least designed) equipment that already purports to do what would be needed in the necessary respects. (Yeah, I know, looks like crank science, but really isn't.)
Actually this would be inferior to IR detectors as IR detectors find impending failures ...
Only if you're using the word 'impending' to describe catastrophic consequences. Anything an IR detector finds is likely already a massive, complete failure as regards bearing or even wheel integrity. And -- comparable to the situation at Marysville -- it's a crapshoot whether such a problem that has progressed to such an extent fails before or after it happens to pass by a wayside detector and generates enough warning to stop the train. If I recall correctly this is one of the reasons for increasing the number of detectors, and I'm not questioning that idea in the least...
... this detector would [not] find failures unless you are proposing sensors on all eight bearings. How many hot box setouts are there without a derailment? The vast majority I would bet.
Not really all that difficult, technically -- although remember we're talking about derailment detectors, not hotbox detectors, at this particular moment. I for one prefer the idea of a device that detects bearing failure more directly, finds and alerts on broken axles with appropriate immediacy, and can do some correlation or sensor fusion with other sources of information.
This does presuppose something 'more' than the reported Spanish detectors (which, however, could be 'improved' at least imho by incorporating a few simple things like recognition of sideframe/bolster vertical angle and rate-of-change information on truck rotation and skew).
Even better are the acoustic [note sp. if not a typo] bearing detectors that find bearing defects long before they become impending failures.
Yes, but there apparently have been problems in isolating some of the acoustic components of the signal from other noise a wayside acoustic detector would pick up. I wholeheartedly affirm that acoustic detectors ought to be placed at least as densely as IR detectors -- that is to say, ultimately at short enough intervals (at least where HHFT trains and their outsize public 'concern' run) to provide at least political assurance that a developing 'derailment cause' will be caught before it is likely to cause an actual derailment. In fact I think it makes sense to have both IR and acoustic wayside detectors even in situations where some form of 'derailment detector' is provided on individual cars.
The problem that Euclid has identified, to recap briefly, is that there really is, and I agree in some ways with him that there can't be, any way to make a HHRT tank car particularly physically safe in a derailment as things currently stand. That means that the industry must concentrate on things that reduce the likelihood of derailments, even when the causes of derailments occur quickly or unexpectedly. (It would be nice if derailments could be prevented with 'perfect' attention to equipment maintenance, wheel grinding, axle or wheel NDT (and why not?) and the like, but I think there is still a significant constellation of derailment causes that happen even if the train's equipment and the track pass their testing. And I think those, too, need to be detected -- certainly while there is any chance of preventing an actual derailment. If there is an actual derailment event, I think there would be clear advantage in passing knowledge of it to the crew as promptly as possible, even if there is no cost-effective way to assure 'automatic stop' in minimum time or distance in that particular instance.
The 'other half' of the problem with Bakken/Eagle Ford HHFT traffic is the undocumented volatile content. I'm certainly no expert, but I think that mandatory degassing before shipment (or whatever that's properly called) will go a very long way to addressing the 'real' public problem, the incidence of fireballs and catastrophic sequential thermal breaching in oil-train accidents (even those that seem to be comparatively slight). THAT is where the Federal agency people and politicians ought to concentrate attention, particularly now that it seems railroading is losing much of the 'cash cow' traffic that would fund mandates like Feinberg's proposed ECP instantiation.
WizlishOnly if you're using the word 'impending' to describe catastrophic consequences. Anything an IR detector finds is likely already a massive, complete failure as regards bearing or even wheel integrity.
Well not really. Modern IR hot bearing detectors are set up in the back office so the deteector tracks the temps of the individual axles. If one axle is trending hotter over several detectors, it will alert and that car can be set out. A significant number of "hotbox" alarms are false positives.
And -- comparable to the situation at Marysville -- it's a crapshoot whether such a problem that has progressed to such an extent fails before or after it happens to pass by a wayside detector and generates enough warning to stop the train.
Its my understanding that the recent derailment was an axle failure (not a journal failure). There are no detectors for axle failure (it is an incredibly rare failure) and the detection is usually after failure when it hits the ground or puts the train in emergency.
If I recall correctly this is one of the reasons for increasing the number of detectors, and I'm not questioning that idea in the least...
If you put a hot box and dragging equipment detector every mile (IR or acoustic) it wouldn't have detected an axle failure prior to failure (nor would it have detected a center beam failure, a side sheet failure, a draft gear failure or any one of a hundred other possible component failures).
Dave H. Painted side goes up. My website : wnbranch.com
dehusman Wizlish Only if you're using the word 'impending' to describe catastrophic consequences. Anything an IR detector finds is likely already a massive, complete failure as regards bearing or even wheel integrity. Well not really. Modern IR hot bearing detectors are set up in the back office so the deteector tracks the temps of the individual axles. If one axle is trending hotter over several detectors, it will alert and that car can be set out. A significant number of "hotbox" alarms are false positives.
Wizlish Only if you're using the word 'impending' to describe catastrophic consequences. Anything an IR detector finds is likely already a massive, complete failure as regards bearing or even wheel integrity.
What I meant was 'by the time something like a bearing problem has become visible to an IR detector, it will have been suffering consequences of failure long enough to be running hot, and as you accurately note, probably in the context of progressing to heating up enough to trigger the detector during the time from the last wayside detector check.' (EDIT -- I missed one of the points here, which (as will be subsequently discussed in more detail) the detector system notes increased heat-trace trends per axle, even when well below 'failure' threshold, and this is likely what both buslist and Dave were discussing. Consider that point made as stated, and if we assume that the train is correctly stopped and an inspection made each time such a temperature trend is detected, my comments regarding that aspect of the IR system are incorrect.)
I don't want this part of the discussion to turn into the pros and cons of thermal detection of bearing failure, which isn't the topic at this point (even if it is one cause of possible derailments). What I'm looking at is continuous detection of derailment 'signatures' and appropriate notification action (which, again, is NOT 'automatically putting the train in emergency every time a possible derailment state is detected).
And -- comparable to the situation at Marysville -- it's a crapshoot whether such a problem that has progressed to such an extent fails before or after it happens to pass by a wayside detector and generates enough warning to stop the train Its my understanding that the recent derailment was an axle failure (not a journal failure). There are no detectors for axle failure (it is an incredibly rare failure) and the detection is usually after failure when it hits the ground or puts the train in emergency.
And -- comparable to the situation at Marysville -- it's a crapshoot whether such a problem that has progressed to such an extent fails before or after it happens to pass by a wayside detector and generates enough warning to stop the train
Again, 'comparable' only in the specific sense that a wayside installation -- here, the dragging-equipment detector tdmidget mentioned -- would not likely have helped the situation, unless it 'just so happened' that the broken equipment passed over it before the failure progressed to an accident. However, an onboard detector would have caught this almost immediately. I do think it is fair to say that it is 'comparable' to note this both for the Marysville incident (as supposedly detectible/preventable by dragging equipment detectors) and for other causes of derailment as they might be detected solely by wayside installations.
If I recall correctly this is one of the reasons for increasing the number of detectors, and I'm not questioning that idea in the least... If you put a hot box and dragging equipment detector every mile (IR or acoustic) it wouldn't have detected an axle failure prior to failure (nor would it have detected a center beam failure, a side sheet failure, a draft gear failure or any one of a hundred other possible component failures).
I've had to stop many times to do bearing checks requested by the "back office" Dave speaks of. Both as a conductor doing the actual inspection and as an engineer, just stopping to allow the conductor to go back. The requests from the hot-bearing desk come, like Dave has said, because a specific bearing(s) has/have been hotter than the rest of the train over consecutive detectors. That doesn't mean the bearings set off any of the detectors, the heat difference wasn't enough to do so. That's why they request a field check before it gets bad enough to se off the detector.
Often, the check of the car doesn't find a failing bearing, but a hand brake not fully released, an air brake that doesn't fully release due to defect or a retainer some how set to a retaining position. If those conditions are corrected, the car is good to go.
The last time I remember having to stop to check a car, we had to interupt the dispatcher for a moment. We were about to clear a detector and get the exit message. It was "no defects" and then the dispatcher told us to stop and inspect a car. The conductor found a slight hand brake.
Jeff
How are "axle problems" detected currently?
schlimmHow are "axle problems" detected currently?
Mostly, as he said, by the method in the old engineering chestnut "Don't exceed maximum loading" -- what's that? "Oops, it broke"
I'm sure at least some sections of axles are NDT tested when a wheelset is taken out of the truck for some reason, perhaps each time the wheels are turned. As noted, there's presently no good way to perform 'direct' testing with the axle in the train, and a visual inspection is probably not likely to show anything in many of the areas where axles are likely to break.
I recall seeing at least one paper that talks about vibration signatures in the wheelset that can indicate incipient axle failure from progressive crack propagation. I don't have the reference but I suspect buslist would know. My suspicion is that in the practical world, the situation is normally taken care of by good quality control and by taking wheelsets out of service before axle cracking can start (or at least become critical).
Whether or not there are nonlinear causes of stress raising in HAL wheelsets, I don't know, but would be interested to find out about them if so.
EuclidThis has gotten me interested in broken axles, and it raises some questions that have been mentioned in the comments above by Wizlish. It seems that broken axles are uncommon, but are often cited as the cause of derailments. First of all, I would like to ask if the term “broken axle” include axles with ends burned off due to bearing failure. If it does, how frequently do axles break due to that cause versus just snapping cold? Other than bearing failures, what causes an axle to break? What can be done to prevent it? If an axle breaks, are there any indications ahead of time? What are the axle failure modes besides bearing failure? Other than overloading, is there anything in operation that can damage an axle? Can rough track cause overloading of axles?Axles
Axles are, I believe, heavily overdesigned precisely because they see such high and relatively unpredictable stresses in service, and because the result of many failure modes can be essentially (or quickly) catastrophic
Following are my opinions. Don't trust 'em without more evidence, proof, and actual experts' opinions..
I would think that there's a difference between an axle end burning off due to bearing failure, and a wheelset seizing and sliding (with substantial heating of the axle but without the axle actually separating) due to bearing failure. So yes, I'd rank a burned-off axle failure as an axle failure (and in part this is because the consequences of this, in an accident, are those of axle failure rather than, say, a frozen bearing causing a wheelset axle end to kick out of the sideframe.) But it's not up to me, it's up to whoever compiles the statistics (in the United States, the FRA).
EDIT -- they consider journal failure from bearing overheating its own failure code E53C; note that for 2014 there was no corresponding E53L reported for locomotives) and provide it smack-dab in the middle of other axle failures in the coding and in the reports from the very useful tool schlimm provides below.
I'd find the risk of an axle in otherwise good condition 'snapping' under any load applicable either in service or an accident to be relatively low. Most of the failures will result from some form of crack propagation, probably associated with the reversing stress in parts of the axle as it rotates under load. There are various factors that would make cracking start, and others that would make cracks propagate dangerously. Various kinds of lateral and vertical road shock might, for example, be contributing factors. Personally I think the likeliest source will be repetitive shock from wheeltread damage -- and I expect the current emphasis on keeping wheels in heavy service turned and well-profiled will have a great deal to do with limiting axle cracking.
Someone in the industry can discuss relative approaches concerning corrosion, particularly in the outside and inside of the 'fit' between the axle and a wheel. You will notice the careful radius/fillet that is provided in good wheelset designs precisely to limit cracking in these regions.
It's possible that there are some 'levered' loads due to lateral flange force or impact. Again, you'll want an expert to explain precisely what the magnitude of peak force here is, and how it propagates up through the wheel; I can't do it for you. I can only note that it was observed a while back that the recorded peak shock force in g recorded on tested Amtrak wheelsets could be in the 180g range, which even if of relatively short duration seemed surprising to some of the better heads on this forum.
I'm going to sit back and watch as more experts flesh this subtopic out.
http://safetydata.fra.dot.gov/OfficeofSafety/publicsite/Query/inccaus.aspx
FRA, all causes of various rail accidents, 4/2014 to 4/2015:
Very few (4-7) caused by axle problems. More from bearing failures (26). Human errors of many types are the largest cause (736), the worst being switches not properly lined (101). Track problems are fewer in number, but caused greater dollar damage ($92 mil. out of a total of $300+ mil.).
WizlishI would think that there's a difference between an axle end burning off due to bearing failure, and a wheelset seizing and sliding (with substantial heating of the axle but without the axle actually separating) due to bearing failure. So yes, I'd rank a burned-off axle failure as an axle failure (and in part this is because the consequences of this, in an accident, are those of axle failure rather than, say, a frozen bearing causing a wheelset axle end to kick out of the sideframe.)
An axle failure is when the axle itself breaks.
The end of the axle burning off due to a failed journal is something else, that's a journal failure.
Two completely different things.
A frozen bearing does normally cause the axle end to "kick out of the side frame" (not sure what that would even be). If the bearing freezes then it still turns in the side frame until the friction with teh side frame burns through the bearing race, then it burns through the axle end until to side frame drops. That's how a bearing burns off. Nothing "kicks out".
dehusmanThe end of the axle burning off due to a failed journal is something else, that's a journal failure. Two completely different things
Keep reading one more sentence - I edited some of that this morning after checking the link schlimm provided about how the statistics were tabulated.
A frozen bearing does not normally cause the axle end to "kick out of the side frame" (not sure what that would even be).
Neither am I, come to think about it.
I thought there were incidents where a seizing bearing would cause the wheel to slide, or 'flat' it enough that the vibration would cock the piece between the bearing and sideframe or actually knock the axle out of the seats; that's unlikely, for reasons you indicate.
EuclidWhen dynamic brakes are applied, is the application developed in stages of progressively increasing retardation?
Yes. I expect a number of people here can and will provide you with detailed information on the right use of dynamic brakes, links to manuals and other information, the history of this form of braking, etc.
In general, you would want to apply dynamic slowly at first, to get the slack bunched properly, then with proper modulation to prevent wheelslide.
Is it possible to apply them to the full intended force instantly?
Obviously not 'instantly': there will be some time constant while the magnetic field builds up. Obviously not nearly instantly; the magnitude both of the peak current and of the effective risetime should be controlled (to prevent damage to the equipment). Obviously not so quickly as to produce even momentary wheelslide. Dynamic (or regenerative) is not an emergency brake, and to my knowledge even where it is a component of blended braking, it would be applied relatively slowly compared to the pneumatic brake.
If it is possible, is there any reason why this should not be done?
There is EVERY reason why that should not be done. The potential gains from a couple of seconds' worth of high counter EMF would not justify the safety issues, or the wear and tear on the equipment, or the very real likelihood that something in the dynamic/regenerative brake would fail or degrade unespectedly and remove its contribution to safe stopping just at the moment you would put especial reliance on it.
This made me think of one of the responses that was tried during the wreck of the Federal at the time of Eisenhower's inaugural. A rather obvious thing to do in the absence of air braking would be to try applying motor power 'in reverse' (Dave Klepper will explain why GG1s did not use regeneration for braking). All that happened was that the overload breakers tripped as soon as any power was applied.
Can dynamic brakes be fully released from their maximum application by simply opening the circuit so the brakes instantly release as if turning off a light switch?
I gently suggest that you read up on magnetic induction before you hypothesize about this any further. The answer to your question about 'opening a switch' is pretty much NO. That's as in "HELL, NO!" I could be considerably more emphatic, but will use restraint instead.
When you have a large current being developed through magnetic interaction, interrupting that current also involves interrupting the outrush current developed by collapse of the magnetic fields -- the time constant of which is remarkably short. That will put very high momentary current across your switch contacts while they are still close enough together to develop an arc. That would be very poor engineering.
With respect to the other question: Even if the dynamic came off "instantaneously", you would not see a rebound effect in the draft gear, whether or not the 'braking' locomotive were ahead of or behind the node. The cars have tremendous inertia, and there is inherent damping and friction in the draft gear, so there is no 'recoil action' that will cause any kind of 'violent' runout. I would expect other effects, wind and grade in particular, to be exerting more force tending to bunch or separate cars than draft-gear runout. (Other opinions, of course, welcome, provided they are based on science or experience.)
EuclidWhen dynamic brakes are applied, is the application developed in stages of progressively increasing retardation? Is it possible to apply them to the full intended force instantly? If it is possible, is there any reason why this should not be done?
Dynamic brake handles have notches, just like the throttles. You could probably hack the computer to get full instant dynamic braking, but you cannot do it from the control stand in normal operation. There simply is no reason for it, as trains begin to descend hills gradually and not all at once.
EuclidSimilarly, what is the method of releasing the dynamic brakes? Can dynamic brakes be fully released from their maximum application by simply opening the circuit so the brakes instantly release as if turning off a light switch?
Once again, the engineer must notch the dynamic brake handle/combined power handle to reduce braking. There is no need to immediatly stop braking.
The dynamic brake handle has positions, but not fixed notches like the throttle.
Getting into dynamics too fast can cause a car to "pop" out under the right ( or maybe more correctly, the wrong) situations. Getting out of dynamics too fast, or even at all on some heavy grades can cause the headend to run out and break a knuckle. Or pull out a draw bar.
jeffhergert The dynamic brake handle has positions, but not fixed notches like the throttle. Getting into dynamics too fast can cause a car to "pop" out under the right ( or maybe more correctly, the wrong) situations. Getting out of dynamics too fast, or even at all on some heavy grades can cause the headend to run out and break a knuckle. Or pull out a draw bar. Jeff
That is exactly what I wanted to know about release dynamics too fast. What exactly would cause the knuckle to break? When you mention this happening when using dynamics on a heavy grade, what does the heavy grade have to do with the possibility of breaking a knuckle when releasing dynamics?
I should also clarify that my questions are based on the effect of releasing dynamics when no air braking is applied. If knuckle breaking from releasing dynamics can result, what causes the run-out that would break the knuckle?
Wow, still going? [crawl back under my rock]
Yup, ever heard the term 'beating a dead horse'? (I've gotta find a bigger rock)
Euclid jeffhergert The dynamic brake handle has positions, but not fixed notches like the throttle. Getting into dynamics too fast can cause a car to "pop" out under the right ( or maybe more correctly, the wrong) situations. Getting out of dynamics too fast, or even at all on some heavy grades can cause the headend to run out and break a knuckle. Or pull out a draw bar. Jeff Thanks Jeff, That is exactly what I wanted to know about release dynamics too fast. What exactly would cause the knuckle to break? When you mention this happening when using dynamics on a heavy grade, what does the heavy grade have to do with the possibility of breaking a knuckle when releasing dynamics? I should also clarify that my questions are based on the effect of releasing dynamics when no air braking is applied. If knuckle breaking from releasing dynamics can result, what causes the run-out that would break the knuckle?
Thanks Jeff,
Gravity. The head end picks up speed. If there is no air set, any heavy cars start to pick up speed, too. The slack that was bunched starts coming out. Even with air set, sometimes the weight of the engines can be enough to break something. When the faster moving portion finds the right spot where it meets the slower moving portion, snap goes the train.
Granted it may not happen every time, but the possiblity is there. You have to remember there can be a lot of variables. Grades aren't always uniform down a hill. Subtle changes can affect the way cars roll. Cars don't all roll the same. Curves can slow the train. Loads and empties will pick up speed differently. Knuckles and draft gear can have defects or the beginning of defects. (They always ask for a broken knuckle, the percentage of old/new break and where the remnants are located. A good conductor will say 50% old break, you can tell by how shiny the jagged steel is. Then he'll do something to make all the shiny steel of your 100% new break look rusty. Actually, everyone talks about it but I don't know that anyone has ever done this. Anyone want to guess what this process is?) A knuckle that has already began the failure process needs less of a jolt to break completely.
If Im going to get out of dynamics on fairly good grade, I like to do it when the headend is going through a curve. The curvature helps to keep things from picking up too fast. Or when the head end bottoms out and is starting back up in a sag. I take into account the grade, curvature and what kind of train I have as to when and where to get out of them. Not just loads and empties, but type of cars. I watch for the position of cars in my train with cushioned/extended travel draw bars. Today I might do something that I won't do tomorrow, it just depends.
I also take into account the kind of engines I have. The newer AC engines can brake to a stop in most places with dynamics. They are easier, unless they aren't working right, to ease out of dynamics. (You can still get run out with AC.) DC engines seem to be harder to ease out of dynamic. (Some are also harder to ease into dynos. You have to move the lever farther in to get them to respond. UP's SD70m units are a good example. When new they were able to ease in and out of dynos. Now it's like they are all or nothing to begin and reach a point when easing out where they just drop out.)
There have been times when I gave away speed because I didn't think it prudent to get completely out of dynamics until conditions changed. I would rather be a little slower than filling out a break in two form.
Getting broken knuckles and/or pulled out drawbars normally end up being caused by the engineers inability to control slack within the train. Slack run in and slack run out can easily generate stresses that are far beyond the designed strength of knuckles, couplers, coupler shanks and draft gear, especially when the slack situation instantly changes from one state to the other. As trains get longer and longer - there is more free running slack in trains.
I am amazed that today's engineers can move such 'oversized' (10000 to 12000 feet and 15-20 thousand ton) trains over territories that were surveyed and built in the 19th Century by Civil Engineers that at the start had next to no knowledge of what a railroad was, and in later decades figured 20 cars of 20 to 30 feet long and 600/700 tons was large train and taxed the abilities of the motive power of the age.
Never too old to have a happy childhood!
Euclid I assume that the runout of slack is due to the sudden releasing of buff force on the car draft gear units. This release allows the draft gear to rebound from its compressed or buff position, and return to the neutral position. Since this return to neutral of the draft gear would be so abrupt, the draft gear would continue rebounding past the neutral and into the stretched or draft position. Then this abrupt stretch can break a knuckle or pull a drawbar.
No. The only things that can give you runout culminating in a shock will be momentum and gravity. Any force developed by the draft=gear springs extending is going to be a relatively slow push, achieving little acceleration by the time 'neutral' extension is reached. And there is quite a bit of damping in the draft-gear mechanism, too, to prevent loose run-out and run-in (of the type, for example, experienced in trains of British four-wheel waggons separated by relatively long-travel springy buffers). Any 'rebound stretch' beyond the neutral point will have to overcome the substantial inertia of the cars on either side before acceleration could build up to a snatch or shock that would break metal.
Slack run-out if the front end is accelerating with respect to the 'rest' of the train, will be propagating down a long line of cars, each one being made to accelerate a little faster as the draft gear is pulled out with All The Momentum of the part of the train that is accelerating. This is constant acceleration over much greater time and much greater distance than a few little springs and rubber blocks could possibly provide.
Note very carefully what the proper implications of 'keeping the dynamic applied' are -- for example in terms of avoiding too fast a release when the head end can start accelerating unbraked or substantially so.
There have been a few instances where running gear has been given undamped, or severely underdamped, control. One significant example was a Reading locomotive, I remember the story as involving a 2-10-0, on which a clever master mechanic had provided two reasonably stiff coil rprings acting on the yaw of the engine truck. The farther they went, the more critical oscillating frequencies of the spring system they began to discover. After about 70 miles, probably the majority of which involved track-wrecking lateral banging, someone was called out with a torch, who selved the spring arrangement tightly then and there. Note that the key word involved here is resonance -- something that may not be seen between large masses at small travel between hard mechanical stops.
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