and then a light throttle apllication that can move the power just a few feet back?
Suppose that said train stalled because a unit shutdown and couldn't be restarted and you have to double the hill. The slack is stretched out tighter than Dick's hat band and the brakeman needs slack in order to make the cut. You never use the throttle to shove slack into the train. That, along with the weight of the cars you are holding on to could cause unwanted slack to be shoved into the part of the train that is being left. That could cause problems when you return for the second cut.
All of the slack that you need is what is in the units themselves. Put a good holding brake on the train with the automatic brake, then release the independent brake on the units (bailing off the automatic application) and let the units roll back into the cars, then reapply the independent brake. When the brakeman is ready, release the automatic brake and as the brakes release, just enough slack will roll back into the train in order for the brakeman to pull the pin. When that is done, pull ahead far enough so that when he returns to the head end there is enough room that if the train happened to roll back, it doesn't couple to itself. Away you go.
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Very interesting, And to "put a little bit of slack on the train," this means a light or medium brake application, basically what was there to hold the train from rolling backwards, and then a light throttle apllication that can move the power just a few feet back? Knowing how long to wait for the rebond must take a lot of experience and skill, and a knowledge of the weigiht of the train and its distribution along its length? And would the same procedure have been applicable in steam days, assuming no helper engine?
In good weather, you should be able to start the train. That is, if it was not overloaded to begin with. If you got it to where it is with no problems, it should start. Complications arise when the weather gets wet or even if the weather is fine and a heavy dew gets on the rail. Another factor making for bad starting conditions is if there is grease on the rail from "Rail Greasers". This grease can get spread out over several curves and may spread for almost a mile or more if there has been a long rainy spell.
In bad rail conditions. Sometimes you can be moving right along then hit a slick patch of rail. A light frost can kill your progress up a mountain. A light mist is not as bad, but, can cause a lot of trouble. There are a lot of units that the sanders get stopped up, put out very little sand or maybe even run out of sand. Or for whatever reason it just can't cope with slick rail. The wheel slip feature will take over them with a vengeance and the unit will keep unloading until the train stalls (remember that word). In this case, if you are lucky and don't have too far to go to get over the hill, you can cut off from the train and slowly sand the rail over the top of the hill and back down again to the train. If it is just greasy rail or it is not raining hard enough to wash the sand off, the train can be started fairly easily.
Stall. Remember that word? That is what you want to do when you stopping a train going uphill. Plan your stop to where the train stalls with the slack stretched out, using power and graduated light automatic brake applications just enough to first keep the train stretched out and then hold the train on the hill.
In mentioning slack, the visual slack has already been mentioned. What hasn't been mentioned is the slack that occurs at a molecular level. While most think of cold hard steel as being rock solid (so to speak), it does have a certain amount of stretch or let's say "spring". When slack runs out there is also a certain amount of tension and then rebound involved. Those who have ridden the caboose on a heavy coal train coming up out of a dip should know what I mean. First the slack is bunched up going into the dip. As the train comes out of the dip, the slack is pulled out. As the slack gets pulled out to its maximum, the metal all throughout the train stretches molecularly a little bit. When this tension reaches its maximum it will start to rebound. When this happens, it causes a secondary run-in to occur and subsequently another lesser run out until the forces equalize. If an engineer is skilled enough, he can use this to his advantage to help start a train on a hill. If he were to put a little bit of slack in the train, it doesn't take much, he could then release the brakes and holding the head end with just enough power, wait for the slack to stretch out the entire train and then catch it as the rear of the train rebounds just enough to lessen the weight so to speak and get the train moving.
I said I "suspect," not know, and thanks for the correction. Makes sense. And if you cannot start with the slack stretched, then I suppose you have to ask for help or "double the hill" which means asking for help in any case. I imagine it was a lot tougher in steam days, but then use of manned helpers, giving some skill at the rear end, was far more common.
Rainhilltrial By the way, coupler components don't "shatter", they break.
By the way, coupler components don't "shatter", they break.
Having picked up 6 pieces from the remains of a broken knuckle (not counting what remained in the coupler) - some times the do 'shatter'.
Never too old to have a happy childhood!
You don't try to stop on a hill while also bunching the slack!!! Air brakes would be set to hold the train as it stops, and as soon as you start releasing your air the cars nearest the head end will start to roll backwards until the slack is "out" and at that point in time you likely have a broken knuckle. You stop on a grade stretched.
it's virtually impossible to stop a train with all head-end power on a hill with the slack bunched. As you set the air, the brakes apply from front-to-rear, speed sinks toward zero, and the rearmost cars will float slack going in-and-out slightly depending on their weight and the grade, but eventually their air takes and they stop pretty much with the rest of the train.
if you're running with distributed power unit(s) on the rear end, the cars ahead of the DP will be bunched (slack gathered) as you keep your DP units shoving (but throttling down as you make your stop) but that's what rear end DP does.
Diesel locomotives generally don't need to take slack as did steam because electric traction motors develop high amounts of starting torque.
By the way, coupler components don't "shatter", they break. "Shatter" means breaking into many pieces. When knuckles fail, they break into 2 pieces, when a coupler body fails the coupler head and coupler shank break apart (or, rarely, sometimes a coupler head itself will break thru the head itself). Knuckle failures are almost always due to a small crack forming and then growing over time and many cycles of slack action until the crack is big enough to make the knuckle unable to carry the load.
daveklepperComments?
Whew! You have a lot to learn my friend! Think about what you have said for a while.
Yes, it is an art. One that becomes finer when the units don't want to co-operate with the engineer. But, like anything else, practice makes perfect and not the way you suggest!
I suspect that stopping a long freight train on an uphill grade means using as little brake effort as necessary, using the dybamic and independent allowing the intertia of the train to bunch the slack forward against the locomotive, but applying enough brakiing effort at the precise moment necessary to keep any portion of the train from rolling backward. Starting would require moving up the throttle from idle almost immediately after releasing the brakes while the rear brakes have not released completely. It must be a very fine art, and the wrong timing can result in broken kuckles, either because fully released brakes have allowed the rear to start backward movement or because the brakes are sill applied too srongly. Comments?
GM1361 What is taking slack in the following sentence? CAUTION: Taking slack is not a recommended method forstarting a heavy train on a heavy grade. Short brake releasetimes will release the brakes on the entire train, and the rearportion will begin rolling backward while the head portion isstarting forward, easily causing a train separation.
What is taking slack in the following sentence?
CAUTION: Taking slack is not a recommended method forstarting a heavy train on a heavy grade. Short brake releasetimes will release the brakes on the entire train, and the rearportion will begin rolling backward while the head portion isstarting forward, easily causing a train separation.
Couplings between cars have some 'slack' in them - potentially on the order of 1/2 inch to a inch per coupleing + the movement of the draft gear on each end of the car. As train lengths increase, the amout of 'free moving' slack in the train also increases. Improperly controlled slack action is the primary cause of shattered coupler knuckles and pulled out draft gear.
The action described in the 'CAUTION' is a situation where the entire train is stopped on a ascending grade. The engineer has 'bunched' the slack in the train, so that each coupling has the maximum slack distance to move before starting to pull on the car behind it. In the procedure being cautioned, the air brakes are applied on the entire train. As the engineer begins to start the train, adding power to the locomotive consist, he is also releasing the air brakes - pulling the slack out and starting each car individually from front to rear. The caution refers to the fact that the brakes will release on the rear of the train before the starting secquence of pulling out the slack has gotten to the rear of the train. Gravity will have the entire portion of the rear of the train pull against the starting head end of the train as a 'solid unit' with a much higher draft force than the engineer intends with his starting sequence. The high draft force is easily capable of shattering a coupler knuckle or finding the weakest draft gear, thus stopping the train and necessitating additional actions being taken.
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