Slack Action

[wabash1]

Back in the GOOD OLD DAYS of railroading, in rolling country a good Engineer would control slack by Brakeing against the throttle.

What exactly does that mean?

Applying the train brakes a little bit, and then opening the throttle to make the train move anyway.  The brakes cause the train to stretch out, thus the cars don't vary their distance between each other (slack action) as the train moves.

This is expensive in that brakes shoes (and wheels) wearout faster and more fuel is used.  Like riding the brake on your car.

you keep doing that and make the conducter mad by replacing knuckles all the time, throttle braking to me is dropping notches to let the terain control speed just before you get to the bottom of a hill work the throttle toward num 8, keeps streched and no run in. get to top of hill slowly get out of it. speed drops train streched, smooth running, if you dont believe it ask my fully rested conductors when we arrive.

[nbrodar]

Funny thing...although fans, and most new hire remember cabooses fondly, most of the old timers told me that the majority of injuries train crew experienced were from the action of the caboose, or items that came loose in there...that and getting hurt boarding and detraining.

Not many of them miss having to be back there...they are kinda getting spoiled with the A/C and reduced slack up front.

That's the truth.  I've been thrown off or nearly thrown off more then one hind end because of violent slack action.

Yes, I love to model cabooses.  But no, I don't want to ride one full time.  Like I said, I'd much rather ride the locomotive.

Nick

[rrboomer]

For a short period of time the Rock Island had a "Sludge" train which operated from a Chicago sewage treatment plant on the old Pullman Railroad (along Dan Ryan aroumd 125th St) to Seneca, IL.

Whenever you stopped you had to leave the air set. Then you'd spent the next two or three minutes going back and forth about 40' due the the liquid sloshing in the tank cars.

[enr2099]

Sloshers are the worst...like you said, they sit there, not moving at all, and wait till you are shoving into the track right beside them, then decide to creep back just enough to get cornered!

I haven't had any sloshing tanks roll out and sideswipe myself yet, but I have kicked loads into a track with some tanks, the joint made and it looked like they didn't roll too far. I went into another track and watched the sloshing tanks in the track I just kicked cars into slosh their way out the other end.

[Semper Vaporo]

Back in the GOOD OLD DAYS of railroading, in rolling country a good Engineer would control slack by Brakeing against the throttle.

What exactly does that mean?

Applying the train brakes a little bit, and then opening the throttle to make the train move anyway.  The brakes cause the train to stretch out, thus the cars don't vary their distance between each other (slack action) as the train moves.

This is expensive in that brakes shoes (and wheels) wearout faster and more fuel is used.  Like riding the brake on your car.

[WSOR 3801]

It all depends.  I haven't had too many problems, but it takes experience to reduce the problems.  You need to know the territory, where the hills and curves and speed restrictions are.  Our trains usually do not have enough power to rip out drawbars and such, but sometimes we get 4 SD40-2s or more together. 

Using air stretches out the train.  Dynamics bunch it up.  Usually I don't have dynamics available, or the line is too much of a hogback to be effective.  I usually reduce power, and take as little air as necessary to keep the proper speed.  I ttakes time to switch from power to dynos, and then back into power.  When the hills are closely spaced, it doesn't work so good, so just keep pulling and use the air to keep things in check.  It takes a while to get a feel for how to do it.  

Slack sometimes helps.  Helps take some of the shock out.  If you didn't have any, there would probably be a lot more broken knuckles and drawbars.  Roadrailers have virtually no slack, but they are also much lighter than a 286k freight car.    

[JSGreen]

I would guess that with longer trains running today, slack could even be a worse problem than it used to be.  Imagine the possible slack action in the 10,000 ft stack train the BNSF recently ran on the Transcon...vs the 1950's era train of 40-50 cars...

 

I had always "assumed" slack was an undesirable side effect of the coupler action, needing some play in the knuckles to ensure proper operation.  WHich of course led to attempts to soften the blows of slack action, designing cushion couplers, etc. 

Has any work been done to improve the design of the coupler to minimize slack, or do the  possible advantages of slack (starting up one car at a time, instead of 10,000 ft of train all at once...) outweigh the disadvantages?  

[Murphy Siding]

Back in the GOOD OLD DAYS of railroading, in rolling country a good Engineer would control slack by Brakeing against the throttle.

What exactly does that mean?

[edblysard]

Nick...

Sloshers are the worst...like you said, they sit there, not moving at all, and wait till you are shoving into the track right beside them, then decide to creep back just enough to get cornered!

In all honesty, I would rather switch with a full tank car as opposed to one that has a dense residue, or is not completely empty, just because the slack it creates will drop pins, hammer the engineer, and of course, creep back on you when you least expect it.

 

Funny thing...although fans, and most new hire remember cabooses fondly, most of the old timers told me that the majority of injuries train crew experienced were from the action of the caboose, or items that came loose in there...that and getting hurt boarding and detraining.

Not many of them miss having to be back there...they are kinda getting spoiled with the A/C and reduced slack up front.

How about a nice big cut of Hydra Cushion boxcars smack dab in the middle of a switch cut?

The locomotive stops after a good kick...the head end of the cut stops...and the tail end stops too, for about three or four seconds...then all the boxes run out....riding one one is even more fun!

Ed, OOHHHH!!! Been there done that, several times.  What about loaded tanks?  I've had tank cars roll into tracks, stop, sit there for 10 minutes sloshing back and forth, and then roll back at me.

Quentin,

The simple answer to crew's "surviving" in a caboose, is that the engineers were better.  Woe be the engineer that spilled his conductor's coffee.   Also when fuel and labor were cheap, power or stretch braking was an accepted and sometimes encouraged practice.  You'd run the locomotive full out and control your speed with the train brakes.  It burned tremedous amounts of fuel and ate up brake shoes.

Slack provides some cushioning for the car.   It's also a matter of physics.  Slack allows you to start a small portion of the trains tonnage at a time.  Imagine trying to pull 10,000 tons from a dead stop.  With slack you only have to start 100 tons at a time.

Depending on the exact mix of cars, there can be 2 to 3 or possibly more carlengths of slack in a train.

FRED does his job.  There are times when it's nice to have a live body on the rear, but overall, I'd rather ride the head end.

I watched a BNSF empty grain train working it's way through a series of hogbacks recently.  Where I was stopped at the crossing, the locomotives had just passed by me.  The slack was running in, and making a lot of banging noise.  Yet, the locomotives were throttleing up, to climb the next hill.  How does the engineer handle all that pushing and pulling without splitting the train?

Skill.  That's probably the truest test of an engineer's skill.   Depending on the terrain, it's actually possible to use the force of the slack running in to give you a boost up the next hill.  You can also use the run-out slack to help hold you back coming down the other side (well, until the bulk of the train crests the hill).

And yes, they still make metal Slinkies.

Nick

[GLENMARY]

Back in the GOOD OLD DAYS of railroading, in rolling country a good Engineer would control slack by Brakeing against the throttle.

[Rodney Beck]

Hi everyone me beeing a engineer I have an idea on how I am going to run the train when I show up at the yard office, after getting out of the yard I figure out other details on how it will run with in the frist 15 miles of the run, I.E. figuring out how the dynamic brakes and the air will work after getting all the above figured out the rest is staying (1) step ahead of everything else.

 

Rodney

[diningcar]

One more engineering concept which was not utilized in the 19th & early 20th century railroad construction days primarily because of the need to build quickly, and as inexpensively as possible is illustrated following:

With current new construction, to the extent possible, grades are established to eliminate hills and valleys; or to minimize the changes as illustrated by my previous post about the Transcon west from Williams Jct. Another example: on the BNSF Peavine line to Phoenix the 1962 Abra to Skull Valley 39 mile line change had its highest point at MP 53. A continuous accending grade from MP 31 eastward toward Phoenix and a continuous decending grade eastward to MP 89 (which is beyond the end of the line chage at Skull Valley) were designed and constructed. The result is that between MP 31 and MP 89 there is only the one transition at MP 53 from accending to decending grades. And this is DARK TERRITORY with 49 MPH max. 

[Modelcar]

...Yes, as a youngster, I had a nice stairway in our home to let my metal slinky work it's way down.  Thought that was quite awesome.

nbrodar:  Thanks for your input on the slack.

I imagine engineers have to start paying more attention now with what {to me}, seems to be considerably more tank cars in train makeups.

[Semper Vaporo]

My Mother related this story to me several years ago.

When she was a little girl (probably about 7 or 8 years old) she lived in Kansas.  This would have been in 1917 or 1918.  She and her Mother rode in a freight train caboose as paying passengers. 

She said that before the train left, she was swatting at flies and having fun running around in the caboose. 

The Conductor told her: "You'd better sit down, little girl."

She said that she didn't like this stranger telling her what to do and DELIBERATELY didn't do what he said.

She told me she could hear the cars making noises as the train started up and suddenly she was sitting on the floor!

She said she got up and sat on the bench next to her Mother and the Conductor laughed at her, but she wouldn't look at him for the whole trip.

 

[nbrodar]

How about a nice big cut of Hydra Cushion boxcars smack dab in the middle of a switch cut?

The locomotive stops after a good kick...the head end of the cut stops...and the tail end stops too, for about three or four seconds...then all the boxes run out....riding one one is even more fun!

Ed, OOHHHH!!! Been there done that, several times.  What about loaded tanks?  I've had tank cars roll into tracks, stop, sit there for 10 minutes sloshing back and forth, and then roll back at me.

Quentin,

The simple answer to crew's "surviving" in a caboose, is that the engineers were better.  Woe be the engineer that spilled his conductor's coffee.   Also when fuel and labor were cheap, power or stretch braking was an accepted and sometimes encouraged practice.  You'd run the locomotive full out and control your speed with the train brakes.  It burned tremedous amounts of fuel and ate up brake shoes.

Slack provides some cushioning for the car.   It's also a matter of physics.  Slack allows you to start a small portion of the trains tonnage at a time.  Imagine trying to pull 10,000 tons from a dead stop.  With slack you only have to start 100 tons at a time.

Depending on the exact mix of cars, there can be 2 to 3 or possibly more carlengths of slack in a train.

FRED does his job.  There are times when it's nice to have a live body on the rear, but overall, I'd rather ride the head end.

I watched a BNSF empty grain train working it's way through a series of hogbacks recently.  Where I was stopped at the crossing, the locomotives had just passed by me.  The slack was running in, and making a lot of banging noise.  Yet, the locomotives were throttleing up, to climb the next hill.  How does the engineer handle all that pushing and pulling without splitting the train?

Skill.  That's probably the truest test of an engineer's skill.   Depending on the terrain, it's actually possible to use the force of the slack running in to give you a boost up the next hill.  You can also use the run-out slack to help hold you back coming down the other side (well, until the bulk of the train crests the hill).

And yes, they still make metal Slinkies.

Nick

[Modelcar]

....The more I read and understand about how violent slack was and is still on a freight train, I wonder how crew members survived as well as they did riding in the caboose....

Besides all the dangers to crew, how did they ever keep coffee pots or whatever on the stove....

Is it possible the severe "jerking" in starting a train wasn't as severe with steam engine power as in today's current beefy diesel / electric's....?

Even so, if a fact...that leaves the natural up's and down of the profile of the route to deal with.

Sounds to  me like it must have {or could have been}, a very severe problem for the folks riding back on the end of the "sling shot" caboose.

The way one can hear the slack running in and out just by sitting at a crossing gives one an idea of how serious of a problem it could have been out on the high rail with brake action along with changing from down to up grades, and all the rest.

Why is slack so important to have in the railcar design anyway....Is it simply the necessity of having it to start a long consist of freight cars using slack to start pulling a lighter load and then picking up the rest of the train as the slack is taken "up"....?

I believe commuter and long distance passenger cars are designed without slack, if I remember correctly, but of course those trains are considerably shorter and lighter.

When one "see's" the slack running in or out at a crossing and then think what it might be like by the time it gets back to the end of a mile and a half train, it no doubt could be really severe.  I suppose what crew members remain on a freight train are better off riding in an engine cab.

Does "FRED" really do the job on the rear end of the train to the point no crew is really needed there to complete the "job".....?

Just my "fan" curosity.....and .

[edblysard]

How about a nice big cut of Hydra Cushion boxcars smack dab in the middle of a switch cut?

The locomotive stops after a good kick...the head end of the cut stops...and the tail end stops too, for about three or four seconds...then all the boxes run out....riding one one is even more fun!

[Anonymous]

     I watched a BNSF empty grain train working it's way through a series of hogbacks recently.  Where I was stopped at the crossing, the locomotives had just passed by me.  The slack was running in, and making a lot of banging noise.  Yet, the locomotives were throttleing up, to climb the next hill.  How does the engineer handle all that pushing and pulling without splitting the train?

By staying one step ahead of the slinky toy in his head. You remember those metal childrens toy that walks itself down steps? Do they even make them today?

[Murphy Siding]

     I watched a BNSF empty grain train working it's way through a series of hogbacks recently.  Where I was stopped at the crossing, the locomotives had just passed by me.  The slack was running in, and making a lot of banging noise.  Yet, the locomotives were throttleing up, to climb the next hill.  How does the engineer handle all that pushing and pulling without splitting the train?

[diningcar]

Interesting question, and I as a civil engineering type, will leave train ops to a "hogger".

However, as new lines or changes of line are designed slack is given substantial consideration. For high density - high speed lines like the BNSF Transcon it would be a significant consideration and I assume with the double track instalation in ABO Canyon they will emulate what was done between Williams Jct. and Crookton, AZ in 1960.

There the line westward from MP 375 to MP 406 was a decending 1% grade and then a verticle curve was designed to encounter an ascending 0.88% grade. The implemented design was a 10,000 foot verticle curve which minimized the "rate of change" so that slack action in almost undetected.

 

 

 

[Anonymous]

enr2099: You're right about all that. on the downhill grade, if there was a helper on the rear using dynamic braking, then the slack might not be as bad, although it could string-line on a curve.

[enr2099]

Is slack action still a problem on modern railroads?  Heard a few stories from older railroaders about the "ride" the occupants of the caboose got on occasion when the head end got to goin too quickly from a stand still.  How is that prevented today?

Slack action is still as prevelant as it was years ago.  

 

Seems also the the container (3 pak and 5 pak well cars) cut down on the slack as well? Anybody got any info on their performance in that regard?

I have noticed that as well while riding them. I think it is due to the fact that some 3 and 5 packs share a truck between car bodies, not quite as much slack. 

Do they make slack less of a problem for the engineer? what about other types of loads, such as liquids, coal, auto-racks, etc.  Which are the worst?

Liquids in Tank cars slosh about and can cause wicked slack action, a bunch of loaded tanks  behind a string of MT's have been known to slosh about so much, they pop some of the MT's of the rails; I've even heard stories from guys who have had tanks slosh around so much that they have ripped the train apare. Autoracks, boxcars, and centrebeam/bulkhead flats with the long cushioned drawbars can cause a lot more slack action than say a grain hopper or a coal gon.

How to you teach an apprentice engineer the "feel" of stretching out a train? And is failure to do so a cause of busted knuckles and pulling the train apart?

It can be easy to feel the slack stretch out. Pulling on a train too hard can rip the train apart

Do loaded cars and unloaded cars effect slack action differently?

They can, loads behind empties can with slack can pop the empties off the track, or they can act like an anchor and when the crew starts pulling can stringling the empties.

 

Lastly, coming off a steep hill (like Tehachapi) does the dynamic brake system help control slack problems or is that control just a factor of the train brakes? How do you keep them from bunching up going down hill? Does it make a great difference if the cars are loaded or not?

Dynamic brakes use the traction motors on the engines to control the train so yes, they bunch up the slack. Power braking is a good way of keeping the train stretched, but many railroads prohibit power braking as it uses a lot of fuel. With loads, when the slack runs in, you'll feel a bigger "shot in the a**" than you would with empies.  

 

[AT&SF]

Is slack action still a problem on modern railroads?  Heard a few stories from older railroaders about the "ride" the occupants of the caboose got on occasion when the head end got to goin too quickly from a stand still.  How is that prevented today? Aside from no cabooses.

Seems also the the container (3 pak and 5 pak well cars) cut down on the slack as well? Anybody got any info on their performance in that regard?

Do they make slack less of a problem for the engineer? what about other types of loads, such as liquids, coal, auto-racks, etc.  Which are the worst?

How to you teach an apprentice engineer the "feel" of stretching out a train? And is failure to do so a cause of busted knuckles and pulling the train apart?

Do loaded cars and unloaded cars effect slack action differently?

Lastly, coming off a steep hill (like Tehachapi) does the dynamic brake system help control slack problems or is that control just a factor of the train brakes? How do you keep them from bunching up going down hill? Does it make a great difference if the cars are loaded or not?

Thanks.