Coupler load limitations on unit trains?

Here's something to remember when you are at trackside watching a train pass, and you hear the thunder of a harsh slack adjustment.  Maybe none of those knuckles broke right then, but hairline cracks result, and -someday, somewhere after months or years of oxidation in those cracks - that knuckle will break.  Of all the broken couplers and knuckles I analyzed as an official, very few were all new breakage.

 

Also, I would challenge your statement that knuckles break with some regularity.  Let's be fair to our North American Locomotive Engineers, who -- in my experience -- do not regularly break couplers.  The failure rate is actually pretty low when looked at as incidents per thousand car miles, and our contemporary Engineers are pretty skilled at train handling.

Tom,

Sounds like the cases where breakage does occur are low cycle fatigue. What safety measures are in place to keep a consist from running away if a coupler break occurs?

Now that's the kind of answer I really like. Plus the link to a really great website. Thanks Al, much appreciated.

And the knuckle acts as the safety valve by design. It is supposed to let go before the drawbar, lugs, yokes or the center sill goes. It's easy to replace in the field, anything beyond that, the car has to go to the shop.

I've heard of engineers tell of instances where their train went into emergency on them, and their first reaction was to go to full throttle in an attempt to prevent the front half of the train from stopping quicker than the rear half (causing a collision that could result in a derailment). This PCS you describe seems to defeat the stated aim of the above-described method of dealing with a break-in-two.

 

---PCJ

With todays technology, the power automatically goes to idle. So the engineer can put the throttle in any position he wants, it won't do anything.

One day westbound, we stopped at the west end of Strong City, KS. A loaded grain train was in the siding being re-crewed. They had already called the DS to come out on the main, and we were going to have to follow them on their block the rest of the trip. He the got a signal and took off, but got in too big a hurry. He had it all stretched out at about ten mph, and went to what sounded like R-8, with a loud bang, the drawbar pulled out of the first car behind the engine. The engine jumped ahead a couple of car lengths, and stopped before the Engineer could get it bailed off. The drawbar fell between the rails, and the train rammed into the engines which were stopped. The coupler on the rear unit was driven right into the hole in the end of the sill where the drawbar had just come out of. It was rammed in there as far as it would go, and the one that fell out was under the front truck of the car. All this happened before they took the signal, so after a few minutes, the DS lined us up and took us instead.