Bucyrus That said, I never thought I would have heard slack defended.
That said, I never thought I would have heard slack defended.
If you spent some time switching cars - you would learn an appreciation for slack.
It's been fun. But it isn't much fun anymore. Signing off for now.
The opinions expressed here represent my own and not those of my employer, any other railroad, company, or person.t fun any
I must clarify that my statement of perfected railroad practice was only a relative term of reference point. Nothing is perfect. That said, I never thought I would have heard slack defended.
Interestingly, I found this old thread where we hammered out all the pros and cons of slack back in June of 2008:
http://cs.trains.com/trn/f/111/t/129809.aspx?sort=ASC&pi332=1
In reading the thread, I see I still agree with myself on the subject.
Bucyrus I am just saying that slack is a necessary evil. It is necessary to make couplers work without having more complexity and cost. It is evil because it causes damage, injuries, and death. I emphasize the point because I get the impression that not everyone sees the downside of slack. Some might believe that slack is just one more element of perfected railroad practice like wheel flanges and air hoses. Indeed, I have seen references that say slack was invented for the purpose of starting trains one car at a time. I seem to recall dozens of articles and references in Trains over the years decrying slack as the one bad element from the pioneering era that was never gotten rid of. It was always portrayed as enemy number one. Today, better control of slack is one of the primary advantages championed for ECP brakes on the horizon.
I am just saying that slack is a necessary evil. It is necessary to make couplers work without having more complexity and cost. It is evil because it causes damage, injuries, and death.
I emphasize the point because I get the impression that not everyone sees the downside of slack. Some might believe that slack is just one more element of perfected railroad practice like wheel flanges and air hoses. Indeed, I have seen references that say slack was invented for the purpose of starting trains one car at a time.
I seem to recall dozens of articles and references in Trains over the years decrying slack as the one bad element from the pioneering era that was never gotten rid of. It was always portrayed as enemy number one. Today, better control of slack is one of the primary advantages championed for ECP brakes on the horizon.
That explains why the last time I switched a heavy cut of cars, a demon rose from the ground and told me if I continued to take slack then the gates of heaven will forever be out of my reach.
Trains also pick switches, run over derails, go through blocks, break wheels, stumble over brake rigging, stringline, drawbars fall out, and 56,000 other things that can go wrong. No technology is perfect. If you think airhoses and wheel flanges are, then it is obvious you have no railroad experience.
Bottom line: we are moving really big and really heavy things on little metal things. There is no free lunch. Despite what you think, slack is very much needed. Unless we are going to shrink train size down to unprofitable lengths.
I got a kick out of the term "perfected railroad practice" because I don't believe in it. There is "effective" railroad practice, there is "contemporary' or "modern day' railroad practice and there are many, many "here we do it this way' railroad practices. It varies from place to place, application to appication, railroad to railroad, region to region, equipment to equipment, seaons of the year, and year to year as track and cars and locomotion change or evolve. Like so many things in railroading, especially from a fans point of view, there is no one answer that fits all situations on all raliroads all the time or ever. It is part of the fun of being an enthusiast.
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zugmann Bucyrus It is easier to start trains with bunched slack. But other than that one silver lining, slack is the veritable Great Satan of loose car railroading. We would all be richer today had it not been for slack. I think I speak for many here when I say: huh?
Bucyrus It is easier to start trains with bunched slack. But other than that one silver lining, slack is the veritable Great Satan of loose car railroading. We would all be richer today had it not been for slack.
It is easier to start trains with bunched slack. But other than that one silver lining, slack is the veritable Great Satan of loose car railroading. We would all be richer today had it not been for slack.
When we start to talk about slack, it is always "slack" vs "no slack". Wouldn't it be a good thing if car makers started reducing slack from 12" to 8,6,or even 4". Of course slack is necessary, but cutting it in half would solve a lot of issues, right?
Bucyrus Here is an interesting look at Russian couplers. I would have to ponder that action a bit before it would completely sink in. http://www.youtube.com/watch?feature=endscreen&v=I1sGqg8A-_A&NR=1 Here is how those couplers operate. I believe this if five-foot-gage, if I am not mistaken. http://www.youtube.com/watch?v=l_I4G92CAco&feature=related
Here is an interesting look at Russian couplers. I would have to ponder that action a bit before it would completely sink in.
http://www.youtube.com/watch?feature=endscreen&v=I1sGqg8A-_A&NR=1
Here is how those couplers operate. I believe this if five-foot-gage, if I am not mistaken.
http://www.youtube.com/watch?v=l_I4G92CAco&feature=related
Model RR couplers grown into steel.
Never too old to have a happy childhood!
European cars are lighter, often shorter, and some ride on single axel bogies or ridged fixed side frames, so the buffers or bumpers help control the effects of slack and buff forces.
Car construction is also a factor, we use heavy center sills to transmit the forces, a lot of European cars use the frame of the car, the bumpers are spring loaded, almost like a cushioned center sill, so you still have slack, it is just taken up by the buffers or bumpers….
If I remember correctly, a lot of European roads use a form of the link and pin, and one was mentioned in an article in Trains where they actually have a screw together type coupler, not sure what country, the Swiss folks maybe?
And Janey couplers can be “tight coupled” on passenger trains, if you look at photos you can see a heavy rubber rectangular bumper on the ends of the cars directly above the coupler, this keeps the cars from slamming into each other, but also allows some small slack action and sideways movement in curves.
Not all that sure I grasp the last statement about slack being the great Satan of loose car railroading, I know of no single locomotive which could start a 90,000 trailing ton train if the cars were in a “solid” block with no slack, the tractive effort would have to be phenomenal.
An MU’ed pair of SD 70s, or SD90AC might, but not a single, and the force during braking would be out of the world…keep in mind air brakes set up from the from towards the rear, with no slack, the moment the front few cars brakes applied, the trailing cars mass and weight would slide the wheels on the leading cars, one after another as their brakes set until the majority of the train had brakes applied….as it works now, the slack allows the following cars to bunch up slowly, while the brakes are applying rearward, the force of the slack running helps slow the following cars.
European trains are by design and operation a lot shorter and lighter than ours, the forces are less.
23 17 46 11
I think I speak for many here when I say: huh?
samfp1943Appolgise for the earlier post in which I had thought that the Ellicott City derailment had not gotte into this Thread. The effects of 'slack action' as mentioned here is a necessary function that seems to facilitate train handling in North America's longer trains.
The effects of 'slack action' as mentioned here is a necessary function that seems to facilitate train handling in North America's longer trains.
No problem with bringing up that accident. It was only mentioned briefly, and it seems to be highly related to the discussion about emergency applications causing wrecks. We don’t know yet what actually caused that wreck, but we do know it was a UDE. I read that the NTSB is investigating it, so I am sure we will learn all about the cause some day in the distant future. The context of what happened with those two girls is rather haunting if you read the details.
Regarding slack. Certainly, I would not say that the effects of slack action is a necessary function that seems to facilitate train handling in North America's longer trains.
I really don’t know if the railroads today could start trains in every case without bunched slack. With steam, it was routine to start trains with the aid of bunched slack, but steam fundamentally lacked starting tractive effort compared diesels. Steam is like being in high gear all the time. I have read claims that the aid to starting trains was the purpose of designing slack into couplers. That is not true.
edblysard But I flat switch, so no air....and you can really launch a couple of cars with the cushion draft help!
But I flat switch, so no air....and you can really launch a couple of cars with the cushion draft help!
I used to do a lot of switching on a grade with no air. Stop train, slack runs in, lift pin, slack runs out, car goes bye-bye down the grade. Rinse and repeat.
If the slack didn't run in, you could shove the slack in, wait a second to let the slack run out, then the train would recoil, bunching in the slack again. Then pull the pin. Usually wasn't advisable to pull the pin when shoving the slack unless the coupling was pretty close. Sometimes you had to if they didn't want to roll.
Heh... miss those days.
zugmann edblysard And yeah, a nice cut of those old SP cushioned boxcars can have almost a half car of more of “slack “although most of it is simply the cushion action, it behaves the same as coupler slack. Yeah, not the same as slack, but close enough. Plus that can cause UDEs, as well: when the airhose trolley line gets snagged on those cushions.
edblysard And yeah, a nice cut of those old SP cushioned boxcars can have almost a half car of more of “slack “although most of it is simply the cushion action, it behaves the same as coupler slack.
And yeah, a nice cut of those old SP cushioned boxcars can have almost a half car of more of “slack “although most of it is simply the cushion action, it behaves the same as coupler slack.
Yeah, not the same as slack, but close enough. Plus that can cause UDEs, as well: when the airhose trolley line gets snagged on those cushions.
Appolgise for the earlier post in which I had thought that the Ellicott City derailment had not gotte into this Thread.
Thanks, Balt ACD for your information, and insight. And to Ed B and Zug for their particular insights. The discussion about the slack action in trains is really interesting, but It leads me to ask another couple of questions, in the line of train handling.
In Europe, and the UK they utilize Buffers on their equipment. I have seen videos of the their coupling process where they push the Buffers to get slack to couple (tight couple?) their cars and power together. Would Buffers work in a North American environment, or do the Janey couplers preclude a need for Buffers? Additionally, would the use of Janey Couplers be a better system that that currently used in Europe, and the UK?
I know European, as well as trains in the UK are generally no where near the size (length) of trains over here. How does a lack of slack on the European, and UK trains have any effects on their train handling?
How does an Emergency Brake application effect their trains?
Do they suffer spontaneous derailments after a severe braking action?
Do they suffer 'stringline style derailments
Thanks
Zug beat me to it…even on the flat swamp of the PTRA, slack is necessary with the loaded coal and coke trains and the unit grain trains, not to mention the 100 car plus yard to yard transfers we run.
Unless you severely overpower the train you still “work the slack” the same as with the steam locomotive mentioned, get the first one moving, it helps starts the second one, so forth and so on.
Time it right, and you can do some really cool switching with them, but your engineer will hate you for it!
Bucyrus Link and pin couplers had considerable more slack than today’s couplers, and they also had a tendency to override each other vertically with a severe run-in. They needed more slack because there was less standardization in the coupler dimensions in that era of coupler manufacturing. Link and pin hardware would not necessarily even mate. In the steam era, slack had a benefit of enabling an engine to start a train one car at a time. But that has never been the core purpose of slack. Moreover, that one advantage of slack is not needed in this era.
Link and pin couplers had considerable more slack than today’s couplers, and they also had a tendency to override each other vertically with a severe run-in. They needed more slack because there was less standardization in the coupler dimensions in that era of coupler manufacturing. Link and pin hardware would not necessarily even mate.
In the steam era, slack had a benefit of enabling an engine to start a train one car at a time. But that has never been the core purpose of slack. Moreover, that one advantage of slack is not needed in this era.
Slack is not needed, you say... hmmmm.... I'll have to disagree with you there. Today's engines are good, but there are still many times you need to take slack to get moving.
And as far as slack today, ever see the slack on a long cut of cushioned-drawbar boxes?
schlimmIs there any thought about reducing the slack between coupled cars in the US?
Yes, there has been a passionate desire to eliminate slack, especially in this diesel era of the longest trains. Slack is a natural occurrence with couplers. They have to close to the point where the pin drops. To make sure the coupler gets to that point, it has to go past that point somewhat. That extra travel to make sure the pin drops is the slack.
That coupler slack amounts to 1” per coupler or 2” per coupled joint.
Once you introduce that coupler slack, it runs in and out as the train travels over the line. That run-in and run-out creates rolling shock waves that travel from one end of the train to the other. The run-out waves can accumulate a tension force to the point of breaking a knuckle or pulling a drawbar right out of a car. Run-in waves can build compression force to the point of buckling the train or a car frame. Both run-in and run-out can cause a derailment in addition to damaging rolling stock and causing loads to shift.
Because of these shockwaves resulting from coupler slack, a cushioning system is needed to help absorb the force before it can build to the point of causing damage. This is accomplished by adding spring mountings of the coupler drawbar to the car center sill.
This spring mounting adds another 5” of slack per coupler, or 10” per coupled joint.
Slack could be eliminated by a feature at each end of a car that would push against a corresponding feature on the adjoining car after the couplers mated. I am not knowledgeable about European coupler systems, but I believe some, if not all, use this method of eliminating slack. Whatever slack-elimination system is used, it requires more complex coupler systems. However, the added hardware would be offset somewhat by the ability to eliminate the spring cushioning of the drawbar to the car center sill.
Why? It is there to make the whole less rigid and able to take curves, roller coaster rides, and for locomtives to be able to start long trains easier..one multi ton car at a time. Remove slack and you remove maneuverability...
Is there any thought about reducing the slack between coupled cars in the US?
C&NW, CA&E, MILW, CGW and IC fan
Semper Vaporo Bucyrus I wondered how the severity of slack could have any effect. I assume the answer is: the greater the severity, the greater the slack distance between each car, and therefore the greater the potential to rotate the glad hands. The slack between cars is the same no matter how many cars there are. And it makes no difference how much a whole train stretches or compresses, the distance between cars is uniform of about 1 ft variation. I suppose the more cars the more glad hands that might have a problem, so the chances of a problem is increased.
Bucyrus I wondered how the severity of slack could have any effect. I assume the answer is: the greater the severity, the greater the slack distance between each car, and therefore the greater the potential to rotate the glad hands.
I wondered how the severity of slack could have any effect. I assume the answer is: the greater the severity, the greater the slack distance between each car, and therefore the greater the potential to rotate the glad hands.
The slack between cars is the same no matter how many cars there are. And it makes no difference how much a whole train stretches or compresses, the distance between cars is uniform of about 1 ft variation.
I suppose the more cars the more glad hands that might have a problem, so the chances of a problem is increased.
The distance between cars varies from moment to moment which is slack action. Draft gear in the coupler shank are sprung so that couplers and cars don't just slam against each other. I think there is about a 12 inch draft at each coupler so that when bunched there may be say 3 inches, normal around 6 and stretched 12 inches...on both sides of the knuckels. So normal would be a foot, bunched or slack in would be less than six inches, and slack completely out 24 inches is possible as to the difference in length of the train at each coupling involved. The term slack action actually infers changes in distance and length.
Closed system...yeah...you're right. Then it has to do with the severity of the change in slack and the physical conntections at couplers and air hoses...the verticle and horizontal motions cause either the couplers and/or the glad hands to disengage. Once you have two trains instead of one, with the lead train stopping and the following going faster than the lead...oh, so many different things that could or might happen...the answer(s) have to be in there somewhere...
That wreck was mentioned in this thread in the third post. It did strangely emerge as being directly related to the topic here, and remains that way. However, the story has changed since first being reported. Initially, as I understand it, they said that the train crew saw the girls and dumped the air. And the assumption was that the derailment was caused by dynamiting of the brakes. The derailment killed the two girls.
Now they are saying that the crew never saw the two girls, and did not put the brakes into emergency. So the question is this:
Did something cause the brakes to dynamite, and then the dynamiting cause the wreck?
Or did something cause the wreck, and then the wreck caused the brakes to dynamite?
Those issues perfectly mesh with the discussion here about undesired emergency applications caused by kickers or by this newest revelation of slack action. However, there is also the possibility of a burst air hose or broken brake pipe. All of those causes would be examples of the emergency application coming first and then causing the wreck.
But the wreck could have come first due to a wide assortment of possible causes. I assume that one of those causes could have been bad train handling. I don’t know what possible results might have flowed from too much throttle through that area. It appears that several cars are laid out in line, on their sides.
The news reporting has been insufferable in this instance. On one hand, they have the girls sitting on the edge of the bridge with the train passing two feet behind their backs. And yet the crew did not see them. The train tipped toward them and spilled coal onto them, but the cars did not hit them. They were found suffocated in the coal, still sitting on the edge of the bridge. I don’t how all that works with the train only two feet behind them.
I would say that the train had to be at least 12-15 feet behind them. In one of their photos, they have their legs hanging over the edge of the bridge. I don't see how the coal piles up on someone in that position. I could see it maybe pushing them off of the bridge, but not buying them. It is a sad story.
samfp1943 Maybe my question is appropriate for this Thread? Hope so. My interest is in the derailment in the recent CSX Ellicott City, Maryland next to the B&O Museum. In looking at the photos in this linked Washington Post article @ http://www.washingtonpost.com/local/two-killed-as-csx-train-derails-in-ellicott-city-overnight/2012/08/21/91075334-eba2-11e1-9ddc-340d5efb1e9c_gallery.html#photo=22 The two locomotives are upright and basicly more or less in line with the tracks, the majority of the derailed cars appear to have gone off on the river side of the SX ROW while there does a ppear to be at one point a chock-a-block pile of some of the cars. Looking at part of the derailed train, it seems that at least some of the derailed cars did sort of stringline' (?) Not sure what the train's speed was prior to the derailment, but I am wondering if the pile up was a direct result of an emergency brake application when the engineer saw the two women sitting on the side of the bridge? [ This article, and some others seem to indicate they were on the ROW ( Tresspassing)]. While one of the early article I had read said the girls were sitting on the side of the bridge rail while texting ( time was around midnight?) Reading back through this Thread there seems to have been no mention of this specific derailment, but mentions other derailments caused by Emergency Brake applicatons. Thanks
Maybe my question is appropriate for this Thread? Hope so.
My interest is in the derailment in the recent CSX Ellicott City, Maryland next to the B&O Museum.
In looking at the photos in this linked Washington Post article @
http://www.washingtonpost.com/local/two-killed-as-csx-train-derails-in-ellicott-city-overnight/2012/08/21/91075334-eba2-11e1-9ddc-340d5efb1e9c_gallery.html#photo=22
The two locomotives are upright and basicly more or less in line with the tracks, the majority of the derailed cars appear to have gone off on the river side of the SX ROW while there does a ppear to be at one point a chock-a-block pile of some of the cars. Looking at part of the derailed train, it seems that at least some of the derailed cars did sort of stringline' (?)
Not sure what the train's speed was prior to the derailment, but I am wondering if the pile up was a direct result of an emergency brake application when the engineer saw the two women sitting on the side of the bridge? [ This article, and some others seem to indicate they were on the ROW ( Tresspassing)]. While one of the early article I had read said the girls were sitting on the side of the bridge rail while texting ( time was around midnight?)
Reading back through this Thread there seems to have been no mention of this specific derailment, but mentions other derailments caused by Emergency Brake applicatons.
Statements in news reports I have read indicate that the crew DID NOT place the train in emergency upon sighting the girls trespassing, but not on the track proper. The train derailed and caused the UDE in the act of derailing.
It would appear from the photographs that have been published that the 'general pile up' occured 6 or 8 cars from the locomotives which were traveling at Track Speed - 25 MPH at the time. I would appear that the abrubt stop caused the cars between the engines and the general pile up to string line around the curve. Maximum track speed for the Old Main Line in this area has been 25 MPH - even back in the days (late 50's) when the line was double track.
Semper Vaporo
Pkgs.
henry6Not only are you talking 50 feet in one hundred car train, but also the slack pulling out is more severe fhe further back from car one you go...the jerk action is trementous at the 75th thru 100th!
But we are talking about a pressure change inside of a closed system. The volume of that system can have nothing to do with train length changing due to slack.
But apparently, the closed system can leak as the distance between each car is changed due to slack.
Not only are you talking 50 feet in one hundred car train, but also the slack pulling out is more severe fhe further back from car one you go...the jerk action is trementous at the 75th thru 100th!
I guess that must be what happens. That is, the slack rotates the glad hands. I can picture that if the gasket seal between glad hands were physically upset just a tiny bit, it might allow a leak to suddenly burst through, and that burst might last a second or two as the gaskets reset their new position relationship to each other.
I found a reference that says the free slack in each coupler is 1”, and the sprung slack at each drawbar is another 5”. So, that is 12” of potential slack at each joint.
Isn't the triple valve just a slug of metal with rings and grooves in it that sits in a close fitting cylinder? When the pressure changes on the brake pipe the slug moves due to the pressure differential with the other side of the slug. When pressure is applied in the brake pipe the slug moves such that the rings and grooves allow air from the pipe to be pushed into the air tank on the car and air in the brake cylinder to escape (releasing the brakes). When the pressure in the tank and the pipe are equal the slug is centered in the cylinder and no air moves. When the pressure in the brake pipe is reduced the slug moves the other way and the pressure in the tank is applied to the brake cylinder (applying the brakes).
If the slug is too loose in the triple valve cylinder or is maybe hung up on a burr or something that has kept it from actually centering, then a small jar to the car can cause that slug to move far enough to act as though the brake pipe had a large reduction in pressure, thus appling the brakes hard on that car. Then it might reset in position due to the brake pipe's higher pressure (to re-pressurize the car's tank) and that would be like a rapid reduction in brake pipe pressure and cause the other cars to set their brakes in a ripple effect down the pipe.
I am just surmizing based on my simpleton understanding of the basic triple valve.
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