Over the last few days, I’ve seen a lot of UP and BNSF coal trains and the DPU units are always at the rear. That got me wondering what the advantage is of running the pusher at the rear vs. at 2/3rd of the way back or the like.
Anybody have perspective on that?
Thx
Stack - -
Well, I don’t have the formulas, but they can figure out where the helpers are needed. It’s much easier to have them on the rear, so they can connect and cut off with ease, but you can’t always run a train like that. It seems like Al Krug had the formula on his web site. It has to do with keeping the trains from breaking in two. Usually when it’s a mid-train helper set, it’s because having either all head-end or all rear-end helpers would have put too much stress on the middle of the train, and risk a broken coupler or drawbar. Sorry that explanation is so non-technical, but hopefully you get the idea. Check out Krug’s site. I think he goes into a fair amount of detail about it.
Bert is pretty much correct. If all of the power is on the point, you run a risk (after a certain steepness, curvature and tonnage combination) of a break-in-two. You solve this in one of two ways.
First, is to make two “singles” out of the train. That means making two complete trains where the tonnage is light enough not to cause a break-in-two or a pull-apart.
Second is to place helpers on the train. These locomotives will need to be cut back, somewhere, prior to the steepening of the grade, to prevent any break-in-twos or pull-aparts. But you can puoo much tonnage just as you can pull too much. When you puoo much, you run the risk of pushing light cars off the outside of curves. This, of course, causes a mess.
So prior to that point, the helper is cut in mid-train. Railroads, for somewhat obvious operational reasons, don’t want to have to cut in helpers. Keeping them on the rear makes operations much easier.
Also, when DPU power is being used, the first unit or set of units will go to the marker end of the train with the rear-most unit pointed “backwards”. The advantage of this is that the train becomes bi-directional with the crew “hoofing it” from one end to the other. Also, putting units mid-train in dedicated unit trains such as coal movements and grain shuttle trains is that the midtrain units run the risk of being “loaded” with cargo, which of course, causes a lot of mess and waste. So you will seldom see DPU movements with midtrain helpers.
So why do they always have more units on the front when loaded, and yet more on the rear when empty. I know the part about not turning them. Loaded there are 2 or 3 on the front and 1 or 2 on the rear. Empty it’s just the opposite. Is it only because there is no loop at the unloading site to turn them? You could run one around at the first pull through siding. If this is good when loaded why is it not bad when unloaded? With a 100+ unit train of empties it seems like those boat anchors at the back would have the tail wagging the dog. Since the enginneers of DPU are doing more work than the guy driving straight power does the railroad pay you more money. I will assume you must be trained, checked out and certified to run DPU. [2c]
And we see just the opposite - they start out with one unit on head, one on rear when loaded and two on head when empty.
It will be interesting to see what the answer to this one is…
Mook
I’ve yet to see that here on the UP transcon. All the westbound empties that I’ve seen look just like the eastbound loadeds- either 2-train-0, 2-train-1, or sometimes even 1-train-1, but never 1-train-2.
I would speculate that the biggest reason for not sticking the DPU somewhere in the middle is because of the big fly in the ointment it presents when loading/unloading. And, like kenneo points out, it makes it alot easier to make a reverse move if the DPU is on the end pointed backwards.
The UP’s K.C. MO. double track to St.L.MO is right behind my house. Everyday I see west bounds(empty) that are 1- train-2 and the east bounds ( loaded) are 2-train-1. Across town BNSF’s are usually the same. Not all but most are that way.
Rrandb, I can’t think of any practical reasons to have more power pushing a lighter train. As Brian mentioned, UP has often taken the DPs off the rear of the empties on our line. I’m not doubting what you see, but it’s time to figure out why. Take some numbers–find out whether the power on a train matches that of the loads from a few days before. It may be purely an operational thing.
Also, are both of the rear units running, or on line?
The whole point of the “-CTE” locomotives on UP was to be able to reduce tractive effort of the trailing units in DP operation to prevent buckling the train. Putting an extra unit on the rear doesn’t make sense.
I have yet to see more than one DP unit on the rear–even at Kirkwood, the day I was there.
If it’s an empty, then probably not. One or both is probably off-line.
When midtrain remotes were first used with the Locotrol system, remotes were usually placed 2/3 back from the front to equalize brake response. KCS, with its sawtooth profile, found this to be causing problems and came up with formulae for placement of midtrain remotes which virtually eliminated the problems.
Be glad to. Where is it?
Sorry. Go to http://www.alkrug.vcn.com/home.html. Take some time to look all around, at the photo essays, and the facts and figures. He hasn’t updated it in a very long time, but it’s got tons of good information.
Kenneo makes some good arguments about helper placement, and power placement locations on the unit trains.
Here in Parsons,Ks. All traffic thru is southbound directional running , [northbound’s use the track thru Coffeeville to go back m/t, and to drop and pu trains- there is an inspection facility on SKOL RR that does inspections, and repairs on unit train equipment].
Anyway, the DP power distributioin
So what you are seeing, regardless if they are loads or empties, is that the 2 engines are always on the east end of the trains, with the single on the west end?
Let me add a little more to the discussion. Sometimes (it seems more often recently) I’ll see the DPU facing the direction the train is going, which would totally eliminate the ability for it to then be the lead when they reach the destination. Do they do this just because that’s the direction the locomotive is facing at the time they need it, and once the train gets to its destination there are turnaround areas so it won’t need to become the lead?
Yes and they appear to be dedicated sets. I have not taken pen to paper as in the summer the foiliage is so thick it’s hard to get unit #'s. All units are on with heat from radiators and when stopped for traffic , which can be heavy, the compressors are pop’n. When they roll by the end pairs are pushin but no where near the eastbound loaded one’s. My theory was they are pushing just enough so that it’s not a big mace at the end of a long chain.Must be stub track at both ends or they would always be double leading. I mean if there is no reason to Y them or run one unit around why would you? Single lead is making big noise when lights are green and 2 trailing unit are only making the same noise level from both engines combined. My question is can the engineer feather back the trailing units where they are not pushing but not dead weight either. I remember early LOCO-trol systems were not very good at that.