Is there a mechanical lock that prevents a reverser control from being placed into reverse while a locomotive is moving forward and vice versa? Or, as an alternative, is there an electrical control equivalent that would prevent a locomotive from loading in reverse while it is moving forward? Or is there some other variation of this concept?
If so, has this been the state of the art since the first diesel locomotives? And if not, when was it first introduced?
Old operating manuals used to mention the last resort for stopping an otherwise unstoppable engine: putting it in reverse and throttling to Run 1, no higher, which it said would lock the wheels.
The reverser on a “standard” control stand have a spring loaded mechanical detent or gate switch between the neutral and forward/reverse positions, but no form of interlocked prevention, you can go directly from forward thru neutral to reverse with out stopping the handle in neutral.
The set up is neutral in the middle, reverse with the handle moved left, forward with it moved to the right.
The problem with going directly from forward to reverse is that this causes a lot of arcing between the brushes and the armature, leaving a lot of carbon scoring.
At slow speeds with light amperage not much damage, but at high amps, it can create enough burn to ruin the armature.
Most of the engineers I work with can go back and fort between forward and reverse while kicking cars, it takes a bit of skill and practice and timing to do it with out damage.
On the newer desk top control stands I can’t say, although they seem to work in the same manner, just laid out in a different pattern.
On a A/C powered unit, I would assume it would not damage anything as there are no brushes, but I can’t say for sure.
Up until 2 years ago, our engineers guide said as a last resort to try and stop, reverse the reverser from whatever position it is in, throttle up no higher than notch 4, apply sand.
This was removed and replaced with a warning not to go directly from forward to reverse or the other way around, as damage to the traction motors will occur.
But the old head hoggers still use that straight thru reverse when kicking, and I have never seen it cause any damage.
I am pretty good buddies with the shop foreman, he said at low amps (closed throttle thru notch 1) it causes no damage, but high amps (notch 5 and up) it can cause a burned spot on the armature.
Thanks Tim and Ed. Ed, when you say that some engineers go directly from forward to reverse during switching, do you mean they go into reverse just before the locomotive stops moving forward? Would they then open the throttle in reverse when still moving forward? If so, I assume they do that just to save time. I am familiar with how the reverser operates on earlier engines, but I have never known what would happen if you went from forward to reverse under significant power.
It is very interesting that manuals used to advise that an engineer could stop by reversing the direction of movement as long as they limited the power. That would almost be like a pro-active dynamic brake, so to speak. So if I understand it, you could slide the wheels by reversing with power, and if there is enough power, it will damage the traction motors. Would it be possible to actually turn the traction motors and wheels in reverse while moving forward?
The only time I’ve heard of someone using that technique (called “plugging,” IIRC) involved wet rail, a pretty good downgrade, and a light locomotive. It wasn’t pretty, and may well have damaged the locomotive.
The old heads time it so just as the train and switch cut stop, they bail off the independent, and have the locomotive in reverse while opening the throttle.
They use the “back” slack to their advantage also…when you kick cars you use the switch cut almost like a whip crack, for want of a better explanation, your cracking the whip and because the last car has its cut leaver lifted, (the pin pulled) the energy can almost pop the car down the track…as the slack runs all the way out the cars then rebound, bunching up the slack., the old guys will time it and just as the back slack reaches the locomotive, they already are stretching or pulling back, so the backward momentum and the locomotive pulling are almost matched.
They use the recoil to get the entire thing moving almost at once.
The eerie thing is how quite it can be…you hear the slack run out with the stop, and you hear it begin to run back in, but then it gets quite except for a few “clicks” from the slack being taken up as the locomotive begins to out pace the back slack…if you just come to a stop and wait a few seconds, the empties and loads start to bang against each other, you can get a lot of back and forth slack that makes a lot of racket.
You can tell if a old experienced guy is running, all you hear the bang when the slack runs out when he slaps on the independent, you have to listen hard for the run in.
I guess the simplest way to put it is he keeps the train stretched from the moment the kick is done.
As for the story you related, if the engineer plugged the train, (put it in emergency) and failed to bail off the engine air or independent brake, odds are the wheels were locked already…on the other hand, if he did bail off the independent, then reversing and throttling up were a last ditch effort to slow down enough to avoid the collision, but odds are the combined force of the trailing cars inertia plus the emergency brake application would have broken the t
The switching procedure that ed describes above is another one that would make a good short video with multiple cameras simultaneously and good narration to describe it as ed does. [tup]
I second that one! I have found some videos on you tube of “kicking cars” but nothing great.
In my description of that M&StL / Milwaukee Road wheel-flattening scenario, I have always wondered what the engineer intended to happen by reversing. He would have probably gotten the most stopping power just by leaving the independent set up and stay on. I would conclude that sliding the wheels would have less retarding power than braking them the maximum brake shoe force short of locking them.
But what about counter-rotating the wheels against the direction of travel? With that, the retardation would vary and would probably fall off as the speed of counter-rotation increased. But say you are moving forward at 30 mph, and counter-rotating the locomotive wheels at 5 mph. I wonder if that would make more retarding force than just locking the wheels.
With a locked-wheel slide, the wheel surface gets hot, which probably decreases adhesion, but the rail is always presenting new surface, so very little heat builds up in the rail side of the contact. But on the wheel
On newer locomotives the computer programming won’t allow you to reverse the traction motors over a certain speed . The fault will read “Plugging attempted at too high of speed” So much for kicking cars with a dash 8 or newer GE. As far as reversing the motors to supplement emergency stopping (with a train) there really is no added effort. Usually all that will happen is the traction motor pinions will spin on the armature shafts and in some cases the armatures will birdsnest. Now that said, I have used the plugging method myself, with light power. On cold snowy days the composition brake shoes have little or no ability to slow or stop the locomotive. Without conditioning the shoes by trying to keep them hot is the only way make sure the brakes will(may) work. Plugging the motors has saved many shop building doors, derails and hard impacts , especially in the winter.
Randy
One thing that I have learned from this discussion is that “plugging” means to stop by reversing to the direction of travel. It is a curious term because I don’t see any connection of the term to the action it describes. I assume the term originated in the steam era, but why was it chosen? Generally, plugging would mean to block a flow.