Locomotive Engineers and power braking for Slack Control

[joeythetrainguy]

After finding this thread again after many years (and a new account!) I sort of wanted to explain powerbraking for anyone who is starting to train for an engineer position and runs older equipment. I personally run a GP10 on a class 3 shortline with no dynamic braking, and was taught how to powerbrake by two former steam locomotive engineers. I'll keep this simple, short, and sweet. When leaving a station you never want to leave your brakes applied. Starting our passenger train I'll fully release my independent and my train brake, put it up to notch 1 and progressively notch up and down as I feel the slack run out car by car. As you feel your slack run out notch up. notch down, repeat until you feel your slack run all the way out. It's a feeling that's hard to explain to someone when you first start training, but in a little bit you will get the feel for it. After that, I'll do my rolling brake test, and when you do so, never let the locomotive go to idle with the brakes applied, this will have your slack bunch right up and at least keep it in notch 1. On the shortline I run on, out of the yard it's a pretty steep grade downhill, and to ultimately keep passengers comfortable and not have slack running in and out, I will set about an 8 pound reduction (varies day to day), and I keep that reduction set for the most part until the downhill grade ends, always leaving the train in notch 1 at a minimum if the brakes are applied, and traditonally around curves and etc I'll notch up to keep a rolling speed and the slack stretched out. It takes about 15 seconds for the brakes to release, so still keep your locomotive in notch 1 until you feel the brakes released. I hope this helps anyone who has found information on powerbraking to be rather vague online.

[Rick Gates]

Powerbraking, stretchbraking, and cyclebraking are all the same. The terms vary from region to region. All of the replys I have read have merrit however, this form of braking is mostly used on frieght to control start and stops and controlling slack on multiple hills. The main problems with this as mentioned, are the skill and timing of doing this. If not done right you would pull drawbars out or break knuckles. This form of braking causes excessive wear on brake shoes and, the biggest danger is depletion of air in the aux. reseviors on each car without adequate charging time. I was taught by the old heads to use this methd over undulating hills to help control slack in heavy and mixed trains. Also, it worked well to stabalize the ride over a rough spot in the roadbed. We did not use this form of braking in passenger service often except for the latter reason as there was not as much slack to control. This is generally a dangerous practice and is prohibited in most places except by timetable special instruction.[2c]

[Anonymous]

As a passenger train engineer,I have worked with old head engineers, one from the Rock Island RR, one from the C&NW, and one from the CB&Q. All three of them will start the train with the air set. I've done and seen it done many other ways, all of which seem to work equally well as long as the engineer knows what he's doing.

As far as stopping, unless it is downgrade, the best is to keep the slack stretched. And power braking is the best way to do this. Also, we run locomotives at both ends of the train, so powerbraking is a must to keep the locomotives on the rear of the train from running in when the brakes are released. This can normally be accomplished by just placeing the throttle in 1 a few seconds before you release the brakes.

By the way Zardoz, we happen to run two former C&NW F7-A's, numbers 402, and 403. Both of which ran commuter service at some point in there career, and both are still geared for 90

[zardoz]

>If the train was stopped such that the slack was in (against the loco), we would keep a five-to-ten pound reduction on the train to ease the jolt of starting (the independent was set to 30psi, and was insufficient to hold back a unit instantly loading 1500 amps).

This part refered to when operating from the locomotive, and the train was stopped on a downhill grade.
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You can imagine the whack at the cab-car end this would produce if you did this with a fast-loading engine... accelerating downhill (which is presumably the way you get 'slack out' condition on a push-pull consist braking into a station, then releasing brakes completely before loading the engine as this sentence implies).[/brown]

With the F7 & E8's, when making a stop, we shut the throttle off (to take the locomotive out of paralell), apply the train brakes, then as the train was coming to a stop (around 20mph) we would put the locomotive in the first notch. So if the station stop was being done correctly, at just the right time we would release about 10-15psi of the full application, that way the train did not do a "stand-it-on-its-nose" type of stop (which results in the passengers being thrown back into their seats at the complete stop). So with the reduction of braking effort, the loco in the first notch would gently bunch the slack when stopping. We then left the entire train's brakes applied, and when it was time to depart, we could go to power immediately while releasing the brakes, and the train would start smoothly as one piece.

With the F40PH's, the units had "blended braking", so use of the throttle of course defeated the dynamic brake, so this method was not used. In fact, it was prohibited by the Metra, as there were some problems with the locomotive wheels overheating due to the friction braking effort.

It is not possible to access the locomotive independent from the cab car. The coaches and locomotives do have 27-point jumper connections, but due to the limited equipment in the cab-car, the operational capabilities are few. It is not at all like 'MU'ing another locomotive. The cab-car has a set of throttle controls (reverser and throttle, but no dynamic brake control), headlight control (for the cab-car only), whistle, bell, and that's about it.

The only time we would use the parking brake (independent) on the cab car was when the train was stopped on a downhill grade, just like when operating from the locomotive. However, the parking brake was used only to augment, not replace, the train brakes. The advantage was one did not need to hold quite as much trainline pressure. However, even with the slack bunched and only the parking brake's resistance to rolling, when an F& or E8 loaded it's 1500 amps, the acceleration was quite sudden; not so much for those sitting (it would not be enough to spill coffee, unless a person was just putting the cup to one's lips), but it would be enough to cause anybody standing to be sitting. Sometimes we would use some slight parking brake assist when just coming to a stop to help bunch the slack. Had to be careful, though, because the parking brake was designed as an 'all or nothing' type of valve, had an unadjustable setting of 90psi, and would lock the wheels in an instant if not done right.


Hopefully this brief explanation helped. I will be happy to clarify any other points.

[Overmod]

I think your explanation is ingenious... but is that what he's saying? I think paragraph 3 is describing what happens with locomotive leading, and paragraph 4 with the locomotive trailing.


>If the train was stopped such that the slack was in (against the loco), we would keep a
>five-to-ten pound reduction on the train to ease the jolt of starting (the independent was
>set to 30psi, and was insufficient to hold back a unit instantly loading 1500 amps).

With the slack in, and 30psi "insufficient", there isn't going to be any relative 'kicking' of intermediate cars in the train, is there? I don't know of anything providing extensive sprung recoil between commuter cars, which is the only thing that would give the kind of surging physics described. That means that the locomotive would be substantially accelerating the whole train at once, and light train-brake application would only provide additional resistance to make the initial acceleration (up to the point that available hp at early notches balances resistance) less 'coffee-spilling'. More support for this:

>This way, the loco would pull on the first car...

Doesn't sound like locomotive trailing to me; that would be loco pushing on the last car, or pulling on the last car in the previous scenario...


>... and some of the momentum would be absorbed by the resistance of the first coach
>(which would get a bit more of a jolt than the last coach), and so on with the rest of the
>train. ...

Again, with the slack bunched and assuming (not biblically ;-}) that "first is last and last is first" you wouldn't be seeing progressively greater jolting on acceleration. That only makes sense in traction.

>So by the combined effort of the engine and train brakes, we could affect a smooth start.

Independent holding down the full acceleration of 1500A on what is (for the first few inches or feet) little more than a light locomotive; train brake as described elsewhere to keep the accelerations on the part of the train that is starting continuously smooth...

And finally:

>If the slack was out, the brakes on the train were allowed to completely release.

You can imagine the whack at the cab-car end this would produce if you did this with a fast-loading engine... accelerating downhill (which is presumably the way you get 'slack out' condition on a push-pull consist braking into a station, then releasing brakes completely before loading the engine as this sentence implies).

I have experienced trailing-unit slack action (on Metro-North, with FL9 power going into GCT) and even at 10mph it can give you a pretty good shock FORWARD by the time the locomotive accelerates the trailing cars progressively while the slack is running out. I'd suspect that an E unit on fast load would provide still more kick...

Finally, he starts the next paragraph:

>When operating from the cab-control car, managing slack was both easier and harder...

which to me implies that he *wasn't* talking about operating from the cab-control car before --

Now, I presume that he's talking about how you start with the locomotive pushing and the slack stretched. I do not know whether it is possible to access the independent brake on the locomotive from the remote cab; I would find it interesting to know. I would think that 'correct' technique would be to have the brakes on and a bit of power applied to 'bunch' the train at final stopping, so slack would be completely out at starting; then you load the unit just before the brakes release so that one or two cars don't have the chance to start rolling before the rest of the consist pushes into them...

>Easier, because the cab-cars did not have an 'independent' brake (they had a 'parking
>brake, but that was not used much due to the incredible noise it made when releasing).
> It was just easier to leave the brakes set on the train when stopped.

Think for a moment about why you would want to set an independent brake on the unpowered end of a (presumably) long consist being pushed by a fast-loading locomotive. It would only make sense if you were bunching slack -- or preventing rollout of leading cars with the rest of the train brake off in the few seconds between release and loading... with the leading independent on, the 'rest' of the train will naturally bunch, which would be what you want; if you were facing uphill the independent on the cab car wouldn't be necessary...

Hopefully zardoz can either confirm or deny that what I've said makes sense.

[mvlandsw]

Originally posted by Alco GE



"Occasionally, before Drawbar Slack was removed from Freight Rolling Stock in the Seventies, an Engineer would Apply and Release the Train Brake to Start a Heavy Train on an Uphill Grade.

On Stopping a Long Freight Train on an Upgrade, the Train would be Stretched Out to the Caboose account the Grade.

When he wished to Lift the Train he knew the Power from the Diesels could Tear the Drawbars out on the First Cars, as the WHOLE Weight of the Train was on the Lead Cars because the Train was Stretched Out.

He would Set the Brake on the Train so it would not Roll Back, THEN Back into the Train with the Locomotives, Bunching the Slack on the First twenty or so Cars, Depending on Grade and Tonnage, Then Release the Train Brake.

As the Brakes Released from the Front back, he would start to Pull Gently, while the First Cars Releasing and Slack being taken Up One Car at a time.

He would then have SOME of the Tonnage Moving and the Momentum would help lift the Standing Cars.

This took skill, and when the Slack Ran out to the Standing Portion you could see everything come to a Stop, then Start again".
I don't think slack has been removed from freight equipment. This method is still used to start trains on grades.

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