Locomotive Engineers and power braking for Slack Control

[AntonioFP45]

Hello guys,

Was very curious about this and wonder if this is still done.

From what I understand; in the past freight and passenger trains often left terminals or stations with the brakes on the entire train partially engaged to control the slack. After getting to the desired speed as the engineer "feels" the slack running out he eventually releases the brakes 100%.

When I used to ride Amtrak in the early 80s the "Silver series" trains were 10 to 17 cars long at times ( I miss those days!). My friend Sam (conductor) would let me stand in a coach vestibule for a while with the upper half of the door open (Heritage Fleet). As the wind hit me at about 30 mph, I remember still smelling the brakes ( stinky!!) for a while after leaving the station. I wonder now if it was because Randall ( SCL engineer and my friend) had the brakes partially on.

Can you guys give some info on this, please? -----Thanks!

[ValleyX]

Rules for passenger trains require a running brake test after leaving the terminal so that's what you were experiencing.

I've never left the terminal with the brakes applied, this is a practice that I'm not familiar with, although I understand that in mountainous territory something like this may be done, I've heard stories of running coal trains east down the mountain out of Bluefield, WV.

Stretch, or power braking is a practice that is actively discouraged because of fuel consumption, dynamic braking is the preferred method by the four large carriers now in the U. S. Sure was a lot more fun to stretch brake, though!

[adrianspeeder]

Powerbrake? that sounds cool. I can do powerslides. Sounds like fun.

Adrianspeeder

[Overmod]

Big, big difference between powerslides and power braked trains. On the other hand, powerslides on locomotives are not much fun at all no matter which way they go... ;-P

I'd always heard of stretch braking being used to DECELERATE passenger trains into a terminal, not leave it (except when the departure is downgrade and the cars don't have tightlock couplers). There's a significant exception I'll mention in a moment.

Now, I've always thought that in the steam era, the brakes were kept applied to reduce the effect of surges on starting, and then fully released once the rpm rate of the locomotive was up to the point the inertia of the cars would damp out the impulses. But that's not what Antonio is talking about, I think.

The exception I noted above is related to electrical multiple-unit operation with only a small fixed number of contactors in the control box. I have observed the following method used to great effect on DC (older NYCTA subway trains, both IRT and IND) and AC (PRR/PC MP54 trains).

There is no 'gradual' way to apply starting power with these trains, as the first available position on the controller is one admitting substantial motor current, and with motors on all the cars the resulting 'starting jolt' is not damped out by much. So, instead, the brake release is modulated so that the brakes are just coming off as the motor torque comes up. The resulting start is smooth as silk, rather than giving a high initial acceleration.

In some cases, the brakes are left slightly applied as the controller is notched up further (I observed this to be typical in IRT subway operation where very high acceleration with loaded trains is utilized) and then completely released when a couple of cars have cleared the end of the platform. Of course, there's some experience needed regarding the load of passengers, the type and length of train, etc. to figure out the best way to work the brakes to get the effect; I saw very few motormen who actually practiced it correctly (but the ride from the ones who did was unforgettable!)

We had some discussion of partial stretch braking technique on freight trains a few months ago -- one place it's used IIRC is when the consist is running over undulating grade and intermediate slack run-ins would occur, midtrain, if some "retaining" air wasn't set. Again, great experience and wisdom is needed to do this.

Stretch braking proper, as I recall, was done both to prevent any slack action from shaking up the passengers during the stop, and to permit a certain amount of 'vernier' precision (in the rocket sense) about precisely where the train would stop at the platform. I remember an article on logging railroads in Trains, many years ago now, which mentioned somebody trying an 'extended-style passenger stop' and yanking log cars apart... the technique may be harder on knuckles and drawbars than it is on shoes and treads...

Very little question, in my opinion, that ValleyX is correct about what you were smelling. I never ceased to be amazed at how stinky the brakes on Clocker service trains in the early '70s got by the time you were at North Philly or 30th Street... guess it's one of the prices you paid for high speed with smooth running back then.

[BaltACD]

Streach Braking is actively discouraged by the major carriers account of the fuel comsumption issue. However, like every rule there are exceptions to it. Many operating territories have specific physical characteristics the require the slack in a train to be accurately controled, otherwise the slack can run in an out within the train and develop enough draft and buff forces to break knuckles or pull draft gear out of cars. Those specific locations where strech braking is recommended are generally taught by the Road Foreman of Engines on the territory affected, and in some cases it may be mandated by a Timetable Special Instruction.

[AntonioFP45]

Very good lesson in railroading!

You guys have a great wealth of knowledge! Really appreciate the input. .

One outstanding point about the above information is that it very plainly shows how tough and challenging being a locomotive engineer is. [4:-)]

Quite humbling when you read the info and realize that just one mistake in slack control could potentially cause damge mounting to thousands of dollars, not to mention personal injury, damage to the track and the loss of revenue. [:0][B)]

With this info, its amazing that many in the public stll think that all an engineer does is sit quietly and push a button to make a train go and another to make it stop, and that's it. I often talk about the railroading to my students and try to dispel the "myths" that they've heard.

Cheers and High Greens!

[zardoz]

On suburban passenger trains there is a definite advantage to starting the train with the brakes set. Despite the claims by some of the tightness of "locktite" couplers, there is still some slack in the coupling (otherwise, one would not be able to couple and uncouple the cars).

Before the F40PH, the CNW used F7's and E8's for suburban service. The locomotives had a switch that controlled the position of the load regulators; unfortunately, it was only a two-position switch (minimum or maximum field). In the minimum position, the unit would load way too slow to keep a suburban schedule, but in the maximun field the unit would load up to 1500 amps with the first notch of the throttle.

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 way, the loco would pull on the first car 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. So by the combined effort of the engine and train brakes, we could affect a smooth start. If the slack was out, the brakes on the train were allowed to completely release.

When operating from the cab-control car, managing slack was both easier and harder. 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. The bad thing about leaving the train brakes on was that the brakes were not charging while they were set, and the stations were so close together that sometimes the trainline would not be fully charged for the next station stop, especially with a longer train.

Even the F40's started quick enough to spill beverages on the commuters if the engineer was not careful.

[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.

• Reply