slack action and other tidbits
all by kabar.
Everybody has heard about Slack Action, but not everybody understands exactly what it is. The railcars are built with couplers that automatically close when two cars are banged together in humping, when humped over a hump crest, or by "flat-switching" the cars in a small yard with no hump. When a switchman cuts out a car on the crest of the hump, he has to do it at just the right moment. The unit powers up in reverse (humping is done in reverse--the unit pulls the string over the hump, then starts backing up so the cars can be cut out, humped, retarded and switched into their new string) and gets the string rolling, then he slacks off the accelerator and the car to be cut (called a "cut") rolls up slowly to the hump crest. When the switchman sees the unit is off the power, he pulls the pin (it's a lever that goes out the side of the coupler) opening the coupler, releasing the "cut" and allowing gravity to roll it into the hump and the master retarder. As the car rolls down the hump, the switchmen in the crest tower hit the MR, and you can hear the squeal of the retarder shoes rubbing the outside of the train car wheels to slow it down. Couplers can handle an impact of about 5 mph, no more. There is another retarder farther down the hump line, called a "group retarder" but I think my local yard doesn't have one. The car rolls until it hits the string of cars in it's CONsist. When it hits, the impact closes the coupler, and it locks automatically.
There is about 1"-3/4" slack in the couplers themselves. The couplers are connected to the "draft gear." The draft gear isn't really gears, it's like "gear" in terms of somebody's stuff, rather than a transmission gear. The draft gear can move in and out about 12"-14" max. So when a unit starts to pull a train, the first car hits slack action after a foot. The second car, after two feet, and so on. On a long train, say 80 cars, the unit may move 85 feet before the FRED moves an inch. Slack action is much more violent in the back half of the train, like the tail on a bull whip. As the train "stretches out", you hear slack coming down the string b-b-b-b-B-B-B-Boom-Boom-Boom-Boom-BOOM-BOOM-BANG! and all the sudden your car is jerked into motion. Stretch out is also called "draft" like in "draft horses." It means "pull." Then, if the engineer gets on the brakes, the train starts contracting the same way, but it's called "buff." It sounds the same b-b-b-B-B-Boom-Boom-Boom-BOOM-BOOM-BANG! and suddenly your car is slowing down. It is now "buffed in." What this means to people in railyards is that they need to be aware that trains can move at any second, especially a long string. The units way down on the other end of the yard may suddenly get powered up and told to move, or get "called." Or the string your car is on can be hit by a midnight rambler at any time, as the hump crew suddenly starts making up a consist. BE ALERT AS TO WHAT IS GOING ON AROUND YOU. Really tight crews have at least one guy (maybe a rookie) serving as a spotter, watching for ramblers, bulls, cops, etc. If you're hopping, you definately need to understand slack action to the nuts. ALWAYS HANG ONTO SOMETHING. Don't ride freestyle or skylining. Only FNG wannabes do shit like that. HIDE. "No exposure without purpose." That's what I think, anyway. (Yo, Collinwood, your shit rocks. "CK, rock like him," and Ride Safe.)
