I am aware of when an engine slips (steam or diesel); too heavy a load to pull or wet rails etc... But what exactly happens when an engine stalls? My understanding is (from what I read) when a diesel stalls, the computer needs to be restarted. Is this true? How about a steam loco? When it slips, it is using a expending a greater amount of steam at a higher rate causing the boiler to expend its steam faster. Am I right so far? From then on, I am lost. What happens thereafter to cause the engine to stall and how hard is it for either type of loco to recover after said stall?

Hello,
While firing PRR 7002 on a main line trip to Gettysburg (branch from York to Gettsburg), with Linn Moediinger as engineer, we had a pilot that insisted we could not make a run for a hill a few miles East of Gettysburg. Anyway, as we climbed the hill the "02" began to slow-----more and more ---and finally came to a complete stop with the throttle completely open. Guess this was a stall !!! No Slipping at all---just wound down to a stop---period!
Linn then asked the pilot just what he wanted to do now and the answer was "back on down and make a run for it---" It was raining and "02" had 75" drivers and what really helped on not slipping was the 68,000# axle load (plus sand), maybe hard to believe but those were the numbers we knew of at the time. Quite an event!
Respectfully,
Dave Griner

I had the 1522 stall on me one time with the booster cut in and the booster slipped down, but the engine didn't. She was a real trouper.

On a diesel, it will keep lugging. As it slows, volts go down and amps go up, into the red, and it is well known how long that can happen before motor damage. The engineer will shut it down before then, or he will fail to do so.

If the latter, I expect some modern locomotives have a safety system to do it for him. Likely a computer. That might need resetting. But it's not like there's something wrong with the computer.

I believe once a diesel train stalls, that's it, you're done. You either call for extra engines, or you go back and cut your train in sections and double/triple the hill. Diesels have a big advantage here over steam; if motors are cool, you can peg the ammeter momentarily to get the train started. But you better get the ammeter back out of the red soon, via either gaining speed or reducing throttle. In a diesel, you can start trains you can't pull.

Whereas I believe steamers have a soft spot in their drawbar-speed curve at zero. They can pull harder moving than stopped; they can pull trains they can't start.

Oo, Ooo, (with apologies to Car 54) I know, I know!!
I think there's a more complex answer to this for steam engines:
The force generated by the steam pressure on the piston is transmitted to the wheel rim by the main rod through the crankpin. The angle that the rod makes with the lever arm from the crankpin through the axle as well as the distances from the axle center to the crankpin center and the wheel rim determine how much of that force is applied to the rail as tractive effort. In short, it's a study in geometry and force vectors.
If you look at that picture, it's clear that at two points in a complete revolution, the TE falls to a minimum (assuming constant steam pressure) when either cylinder is at the end of its stroke and only one cylinder is actually applying force to the rail, and peaks twice when both cranks are at 45 degrees, or when each piston is in the middle of the cylinder and pushing or pulling, adding up to approximately 40% more TE than the minimum. This is because at a 45 degree angle only 70% of the force is applied toward torque for each side.
So once momentum is lost, theoretically stalling will occur as one piston moves to center.
Also, when starting, getting each piston off dead center is important, and once you're moving you will tend to keep moving if momentum carries you past the minimum points.
I think this is right, but will look forward to corrections and amplifications.

While working at Heber, for some reason I was given a old BN rule book to look at. (You know, sometimes there's people that just bring stuff from their gee-whiz collection...) Somewhere in the middle it talked about instructions for operating diesel locomotives according to "short time running" or something to that effect. It was later after I became a diesel engineer that I had a better understanding of what was talked about, although because I briefly read the document, was never really required to utilize the knowledge (see below), and also considering this was over 6 years ago I read it, I may not have a complete understanding.

The ammeter on No. 1011 (NW2 - built in the 40's, so no computer) is labeled for short time running. From what I read, and from looking on this gauge, an engineer in a pinch is allowed to operate at certain areas "in the red" for a limited amount of time before doing damage to the traction motors and other electrical systems. The higher the amps, the less time you get to run at that level. From what I remember, the gauge is clearly marked with the number of minutes allowed at each level. (From 60 minutes all the way down to 1 minute, I believe.)

When the allotted time is up, the engineer is to cease running (stop the train, or coast if possible) to allow things to cool down for a minimum amount of time, usually at least as long as the time spent running in red. So, if you are allowed 15 minutes of running at a particular level in the red, you would need to allow at least 15 minutes of cool down time before starting up again. Depending on the tonnage you're trying to haul and the size of the hill, this could be a very long process, and you might be better off doubling (tripling, quadrupling, etc.) the hill or waiting for help.

Fortunately, while I was at Heber, there was never a real need to utilize any kind of "short time running" on those locomotives. Even where there are steep grades, the train is rarely heavy enough to be a concern.

Here is your answer as to what happens with full stall and wheel slippage is present.
http://www.csx-sucks.com/images/pic/melted.jpg

...here is a better one, I've seen small divots, these are really impressive though!

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The incident in the photos was the result of vandals managing to get a locomotive in the middle of a consist running and leave it in the 8th notch spinning away for quite some time.

The proper term for running at maximum amps is "short-time rating". AC locomotives and many newer DC locomotives don't have manual short-time ratings. On a number of more complex GE locomotives, the "brain" will automatically cut-back on the amount of amperage being loaded to the traction motors after awhile. Older EMD's and GE's - like SD60, C40-8, etc. and older - still do have short-time ratings on the amp meter. Without having one in front of me, I believe that there is around a five minute limit to max amps under 6 mph.

I can tell you from personal experience, if I'm really close to making a grade, will stall and need help if I stop (and have to fill out the subsequent report), and I've reached the end of the time limit for low-speed amps, I'm going for it. The motors probably won't cook on my watch, but I'm sure at some point it cuts into the absolute life-span of the them.

To paraphrase a famous movie line, "I love the smell of burning traction motors in the morning!"

Shouldn't there be 4 pairs of divots?

On most older EMD's the hand brake often only secures the brake shoes on one axle only. So, if the vandals didn't release the hand brake when they got the engine running, the axle with the brakes secured probably would have either burned out the traction motor or tripped an overload relay and shut down that axle.

Back in the 1970's I heard about a Southern Rwy freight with a radio car and midtrain helper pull into Inman Yard here in Atlanta. They tied the train down and then told a new hostler to take the engines to Peagram shops.
The new hostler uncoupled the locos and ran them down to Peagram. All the forward and reverse moves the locos executed were transmitted back to the mid-train since the hostler did not know about mid-train helpers or how to deal with them and therefore did not turn off the transmitter.
The first anyone knew that the mid-train was helper was reacting tot he locos heading to Peagram was when it ground through the rails and fell onto the box cars on the next track over. As I recall there were som 10-odd boxcars that tumbled over. If the train had not tied up in the middle of the yard, someone would probably have noticed.

Doug vV

Several years ago,I had SP 786 just flat stall on a 2 percent grade and a maximum tonnage train. After 10 minutes of wrestling I managed to get her moving again but she never would slip. In January of this year ,I had TSRR 201 get down to about 3MPH,slip,start,slip again,then start. I think only now my left arm is back in place from opening and closing the throttle.