coupler slack

[trainspotters]

I am confused about how multiple engines (front, middle, rear) can control a long drag. It would seem to me that the slack would be changing as different loco's pick up the load. I would not have any problem visualizing how this could work if there was no slack at all, but a 100 car train must have at least 8-10 feet of coupler slack. How can all engines share the load if it is constantly shifting with the changing push/pull of the power units?
Keep on Trainin'

[Jackflash]

There is no change of slack because of the engines on the head end
doing different things, sure some engines in a consist pull harder ect
but while pulling all are doing what it can to move the train, an example,
suppose you have three engines on the head end, the lead engine is
a smaller GP type unit, the second and third units are larger SD units
while under power if you were to walk back and check the slack between
the lead engine and the second engine you would find the slack streched
tight, it would not be bunched or go in and out. all the engines add up
( I think this is what you wanted) jackflash

[trainspotters]

Not really...I was referring to motive power throughout the consist of 100+ cars, and the fact there is much slack in the whole train, not just 3 units at the front. I was trying to get information on the entire train slack, especially when there might be loco's at both ends. Then the slack will change when the rear loco's "push" the slack out of the train.

[jchnhtfd]

Check the 'give me some slack' thread -- there are some really good posts in there from some of the guys who really know and do it for a living!

[dehusman]

Yes the slack changes as the train goes down the railroad, but a reailroad changes over distances of miles, not feet, so the slack tends to stabilize after a while. Plus since the train is effectively broken into smaller "trains" the individual slack forces in any given portion are smaller.

Dave H.

[heavyd]

Did you know that a multi-level autorack car has three feet of coupler draw-bar compression, 1 1/2 feet at each end? If you had a 100 car unit train of autoracks that is 300 FEET of slack!!! I think the old Penn Central used to run 200 car autorack unit trains. 600 feet of slack action, could you imagine that!!!

As for how they control in-train forces I think they can have the mid-train engine apply power or brake independent of the lead units. I think that is the "Locotrol" system. For example if the lead is running up grade it will apply power at the same time if the mid-train helper is still running down grade it will be braking to prevent the rear half of the train running into the front, I think...

[wabash1]

The mid train helper better not be braking this will make the slack come in and what comes in must come out. if i am going up hill and the rear is coming down hill this is what helps keep my speed up. and the mid train helper is in what ever notch i am running on the head end. basics of train handling is after pulling a grade you drop 1 notch this helps take stress off the knuckles . and if you have mid train power when it tops the hill drop another . the reason is you still need to take stress off the knuckles back there. you might have a train that can produce slack but as long as you are pulling steady what little might come in will go out smooth. if you take that mid train power and start making it speed up slow down differant than what the head end is doing you will get the accordian afect and a knuckle or draw bar will result. remeber that mid train helper is just that helps move things equal to what is going on up front.. Dont think of it as a engine that can move a train but more like a car that helps keep things moving you wont get 50 mph out of the mid train helper and 35 from the front they will both keep it going 35 mph or 50 mph equally with out any special controlls. The key is knowing your terrain and your train. Another way of thinking of it is if you ever pushed a car from a place where it was stuck. did you actually ( with your body) supply the main power or assist with the main power. ( the cars engine) in helping it get moving.

[Anonymous]

the answer is try to keep the train either bunched or stretched at all times. you do have changes in the slack as the train goes over different terrain. this is what makes a good enggineer. he knows his territory like the back of his hand and can adjust for the upcoming changes. say like i am going down hill and i know i am coming to a bunch of camel humps. normally if the locos were good i would put on first service on the train and drag it overthe whoop-dee-doos. some casers you woul rather have the train bunched up.all depends on your power, the weather, the train length and weight.

[Mookie]

QUOTE: Originally posted by jchoochoo71

the answer is try to keep the train either bunched or stretched at all times. you do have changes in the slack as the train goes over different terrain. this is what makes a good enggineer. he knows his territory like the back of his hand and can adjust for the upcoming changes. say like i am going down hill and i know i am coming to a bunch of camel humps. normally if the locos were good i would put on first service on the train and drag it overthe whoop-dee-doos. some casers you woul rather have the train bunched up.all depends on your power, the weather, the train length and weight.

Reading right along and doing pretty good - then came to "first service". Ok, now you have to explain that one!

Curious Mookie

[Anonymous]

first service mookie is the first indent on the automatic brake valve handle. the reduction usually gives a 6 to 8 pound reduction in the train brake line. basically i use it to warm up the brake shoes. it does apply the shoes against the wheels but usually not enough force to bring the train to a screeching halt.thats why if you got good power you can drag a train through ups and downs.

[kenneo]

A service reduction of less than 10 lbs also will make the next reduction much quicker in propagation. The auto system jchoochoo71 was mentioning we never had when I was in train service - you got to do it all by yourself by going to the reduction quadrant and then lapping back at the desired reduction.

I've ridden behind engineers that could atke 100 cars up a mountain and as they came over the top, bunch the train so smoothly it was like riding in a passenger train. From full pull to full dynamic without spilling a drop.

[Modelcar]

Previous post just mentioned Passenger train....and I am wondering about slack with that...I assume there is none designed into that system.

[zardoz]

QUOTE: Originally posted by Modelcar

Previous post just mentioned Passenger train....and I am wondering about slack with that...I assume there is none designed into that system.

Correct assumption, modelcar. There is a small amount of give in the knuckles so that the movable part can actually move--just enough 'give' for it to function. The couplers on passenger (as well as haz-mat) equipment used to be called "locktight". I do not know if this was an official name, or a nickname. They have extra structure to hold the cars together better in case of derailment.

[Modelcar]

....Jim, I have noticed the couplers on tank cars have a divice, I believe it is top and bottom of the coupler to do as you say...stay coupled when things do not go right. In thinking about that, I now remember reading how passenger car couplers are designed to keep cars together when a derailment happens and in turn that helps in the effort to keep cars from turning over or becoming a ram and butting into a solid structure, etc...

[TH&B]

You called them "locktight" couplers, I always thought I heard "tightlock". These are the couplers used on modern passenger trains and some coaltrains and some tank cars. They resist twisting and keep the coupler height always acurate and sterefore stronger, even if train derails. There is also the shelf couplers, also used on tank cars and some other freight cars, they help prevent couplers sliding up and down and seperating, especialy in derailments. These coupler types are safer but bulkier than the standard couplers wich are still most commun. But I don't know if there is a variation on loose slack, passenger trains seem to have less slack.

[kwboehm]

I don't know...I've been on a couple of passenger trains that had plenty of slack in them. 4th of July 2002 comes to mind when I was riding back to my friend's house on Metra, and every move the engineer made jerked that train quite a bit, not to mention all the slack running in & out at the stations.

[wabash1]

you start using air and only first service 2 things going to happen.
1) in the area i run your going to get a knuckle .
2) you say just the 6-8 pounds how about bringing the equilizer on down to 10 lbs so the quick release feature on the cars will work other wise you will have sticking brakes.

a good engineer wont need air and let the terrain drag your speed down so you can run from the run in. Now dont get my statement wrong I have run in hills mountains and the flats and each one has its good points and bad.

[Anonymous]

i know what you are saying wabash and i agree. you know you can have the same loads and empties and the same engines and the same weather on the same piece of track and every time the train will act differently. i was just trying to give a generic explanation of how it works. i am sorry if i confused yall.

[Modelcar]

....Really sounds like a problem and that it is always different. Someone say again just why we need to have slack built into each coupler. [On freight trains].

[wabash1]

Ok let me see if i can make this clear in some way. On tank cars covered hoppers gons engines some box cars there is no slack so to say. when these are coupled there is just enough clearance on the knuckles to close . not more than a 1/4 inch ( and that may be stretching a bit) this is built in to have clearance for the closing other wise it wouldnt swing close and if you had pressure on the knuckles you wouldnt be able to lift the cut lever to seperate the cars. Now we move on to super cushion cars. these cars have springs built into the draw heads to easy coupling force on the cargo ( and to a point slack action while rolling) when the cars are humped the coupling forces are great enough to damage cargo. ( cushion cars are made to protect high dollar cargo from damage) now with the 2 differant cars in your train the cushion cars tend to magnify the slack action in your train. cars with cushion dampers are auto racks some boxcars flat cars to name a few. if you ever get a chance to be on a train such as a ballest train they are small and heavy. they will run in and shove you if not prepared for it there is not slack so to say but at 50 mph it seems like you get hit from the rear by another train. but a grain train wont do this to you . ( or at least me it dont) now take a mix train you easy the slack out and in because you have the differant draw heads and weights . then add one more thing to the mix, power take 2 dash 9 engines and 9000 tons you wont out run the slack action of the train the engines wont load fast enough to do this so you get tapped One way around this is while comming down hill is to get after it early and hope you are not speeding while out running your train. now take the same train and say 2 sd60 or 70 they load quicker so you can hold your train back before taking off and going up hill.

Now back to the original question the slack in the knuckle is for the operation of the coupler you haft to be able to get the moving parts to go around each other in coupling and uncoupling. thus if you have 70 cars and a 1/4 inch of play in the knuckle ( you add it up) this is the slack that is built in. a well built train you wont feel it. but if you put the light cars up front and heavy ones on the rear it is very noticable. even though it was wordy i hope this helps.

[Anonymous]

i know what u r sayin wabash. i had a 78 car train one daywith 26 empty hopper up front, another 24 loads behind that and the rest of the cars were those 78 foot bulkhead flats with the cushion drawbars loaded with lumber. i coulnt go from notch 8 to notch 7 without getting tapped.

[TH&B]

OK so it is clear to me anyways why we need slack for uncoupling and switching and stuff, but lets say as an experiment someone got 100 loaded grain cars or more and tied them together with solid drawbars with vertualy no slack like a roadrailer train. The train is 14000tons or more without engines, would this train be easier to handle or would it have its own set of problems??

[Modelcar]

...Thank you Wabash....It really does sound complicated. I understand the 1/4" necessary for the parts to rotate in coupling and uncoupling, etc....and of course the cushion cars with the spring loaded draw bars [heads], what their purpose is. It sounds like a touchy bit of operation especially if the train is on track with up and down profiles. I remember reading of slack action could cause injuries in the trailing cabose if the engineer was not able to control the slack just so and or with certain types of loads on a train, etc....

[jchnhtfd]

QUOTE: Originally posted by jchoochoo71

i know what u r sayin wabash. i had a 78 car train one daywith 26 empty hopper up front, another 24 loads behind that and the rest of the cars were those 78 foot bulkhead flats with the cushion drawbars loaded with lumber. i coulnt go from notch 8 to notch 7 without getting tapped.

Hey guys, I like your definition of 'tapped'[:D]

[zardoz]

QUOTE: Originally posted by kwboehm

I don't know...I've been on a couple of passenger trains that had plenty of slack in them. 4th of July 2002 comes to mind when I was riding back to my friend's house on Metra, and every move the engineer made jerked that train quite a bit, not to mention all the slack running in & out at the stations.

Yea, it's amazing how much slack a passenger train APPEARS to have. However, in reality, there is very little actual slack; it just seems like a lot because us humans are very sensitive to sudden movement. A freight commodity would never notice that amount of slack. A "snitch box" placed in any passenger car would not record any drastic movement.

And just for reference, I operated Metra trains for many years, so I am quite familiar with the slack to which you refer. And like in a freight train, the amount of slack action is largely due to the engineers skills (or lack thereof), and only somewhat due to terrain. The only time any slack should be felt is when starting from a dead-stop, and even then, a little tap is all you should feel..

When I operated the old bi-level equipment on the CNW, some of the first-generation coaches had a lot of play in the coupler assembly. When operating from the cab-car, if one had a long (6-9 cars) train of the old equipment, and went from run 8 to idle in preparation to make a station stop, you could feel the slack run out ahead of the loco; then when the brakes set up on the coaches, (which set much quicker than the loco), the slack action would cause the loco to 'run in' to the train, giving quite a bump to the passengers; if one had a F40 as power, there would be an additional slack movement as the dynamics took hold, stretching the slack back out. A poor engineer could empty a coffee cup without taking a sip.

[wabash1]

Yes a 100 car grain train will pose new problems . first the weight is equal thru the train so the only nessesary train handling ( my area i run) will be not pull real hard till most of the weight is over the hill. this is to keep the draw bars where they belong. It makes a dispatcher mad when you tell him you are in emergency and the conductor found a draw bar laying on the ground slack action is almost nil but as the wieght comes over and lays against the engine it pushes and this feels weird also.

Slack action will hurt a man on a caboose and lots of roads had cushion draw bars on the caboose except the old southern ( i guess they thought we are tough, you had to be )

yes the term tap sound better on the forum istead of what we use on the road. ( getting hit in the a$$) this is the conductor wake up call.