I forget which recent issue of Trains had a short feature on remote coupling/uncoupling of cars, maybe this was part of that system. Of course it would be another expense but I’m sure a train would stop faster and shorter if every car had an air dump valve for when the train goes into emergency.
Faster than what? An emergency application can be initiated from anywhere in a train (the point where the train line comes apart, for example), with the immediate reduction in air pressure triggering the emergency application in the adjacent cars, and on down the line. Since this is a function of air pressure, the emergency application travels through the train (well, the brake pipe, anyway–a few feet per car longer than the train) at roughly the speed of sound. That’s pretty darn fast, and that’s why once you hear an emergency application from trackside, you never forget it!
Theoretically, an emergency application, or any other application, could be triggered at the speed of light. That’s what electronic air brakes are all about. Sounds great, but somebody’s got to make and break the connections when cars are uncoupled–and that involves going between cars and/or time where it didn’t need to be spent before.
The emergency function does cause every car to dump its portion of the trainline volume directly to the atmosphere. So I would conclude that what you are suggesting already is part of the system.
On top of that, doesn’t ECP (electronically controlled pneumatic brakes) allow the cars to dump almost simultaneously (the speed of the electronic signal instead of the speed of the air reduction?)
In a service application, air is vented out of the trainline near the engineer’s brake valve. This begins dropping the pressure in the trainline from the front and progressing toward the rear of the train. As this dropping pressure progresses backward, each car it encounters begins to set its brakes. To fully set the brakes, the entire trailine must exhaust out of the opening at the head end, which takes some considerable time.
However, if you make that opening big enough, the air will exhaust faster. If the hole is big enough, and the rate of trainline pressure drop gets large enough, the triple valve on the first car senses this. In response, that car’s triple valve opens the trainline to atmosphere. This adds another hole in the trainline. Then the next car’s triple valve senses this large rate of reduction, and it opens the trainline to atmosphere. This individual dumping of each triple valve on each car progresses as a chain reaction from the front to the rear.
Bucyrus,
Triple valves were last used with “K” brakes. Correct term for AB and later brakes is “control valve”.
Mac
The big push in Electronic brakes is the delay however. If you figure a 1/100 of a second delay in the brakes, then a 55 car train, the engien is stopping a 1/2 second before the end of the train. With trains apporaching 100 cars or more, one reaches a point where the end of the train begins to jackhammer on the train, or do an impression of the suspended balls on many Movie big business desks. The alst car pounds into the car in front of it, shoving it into the next car, the next car, and soon there’s a noticeableshove on the front of the engine, and it’s attempting to rip the “anchor out of the ground” and shove the whole train out of control. Cause, you’ll notice, twith the air dumped, there’s no brakes. And steel will slide on steel.
A good engineer, at least on short trains, will try to surf the train to a safer stop than slamming on the brakes implicates, but he’s doing that with the loco brakes, and I’m not even sure he’s doing that with all the locomotives.
The trains issue you may be thinking of had the NS and CSX coal trains snaking around each other, I think it was 2 years ago. That hammering I mentioned was their concern, cause in Appalachians. the last thing you want is a train sliding down the side of a mountain.
That’s true, but out in the field the use of Triple Valve is almost universal when referring to the control valve.
Jeff
[quote user=“Bucyrus”]
That chain reaction of concussion-fired dynamite is why the train air brake emergency function is called dynamiting the brakes.
I consider the chain reaction of the air brake emergency function to be the most ingenious feature of the Westinghouse railroad air brake. What triggers the emergency
Each car does dump. Sudden drop in BP pressure puts valve in emergency position. Transmission times are relatively fast but can’t exceed speed of sound. 900 ft/sec is a good number.
[quote user=“jeffhergert”]
[quote user=“Bucyrus”]
That chain reaction of concussion-fired dynamite is why the train air brake emergency function is called dynamiting the brakes.
I consider the chain reaction of the air brake emergency function to be the most ingenious feature of the Westinghouse railroad air brake. </
Is there a easy way to identify and bypass a car with defective brake or do you just “baby” it along?
It’s easy enough to do, but the hard part is figuring out WHICH car(s) is/are causing the problem.
Just an random thought on this here from one who is utterly inexperienced in such things - but here goes anyway:
When performing the Initial Terminal Brake Test after the train is assembled for the 1st time, would it help to find the ‘kicker’ cars by making that brake test by using the ‘Quick Service’ brake application setting, instead of the more normal ‘Service’ setting ?
By forcing the rate of train line pressure to decrease faster that way, it might trigger the ‘kicker’ cars more often, especially those that have the dirty orifices in their brake valves as so capably described by Falcon48 in his post above.
Doing so might help to find it / them while the train is still in the yard, it’s still at rest so there’s no slack run-in or-out to cause a ‘break-in-two’ or broken coupler knuckle, etc., and there are also still some carmen around to help look for the culprit car ?
They use the EOT data these days to find kickers. Knowing when the pressure wave hits the head end relative to when it hits the EOT, one can figure the location in the train that started the trouble.
With the advent of Extended Range Dynamic Brakes, many carriers are instructing the engineer to do most of their braking utilizing Dynamic Brakes rather than the air brakes just because of the potential for ‘a kicker’ when using air brakes. The ability of the train crew, in the field, to be able to diagnose and fix a kicker in their train is just about zero. Cars that are kickers, may not dump the train into emergency 100% of the time…the act of going into emergency may dislodge the offending piece of dirt and the next time the brakes are applied the valve will work as intended, then again the dirt may again block the appropriate orifice and initiate another emergency application.
I recall a story in Trains several years ago where an engineer was blamed for bad train handling in a yard move. He defended himself by saying that he had a kicker in his train. He even went on to say which car was the kicker and where it was in his train. I thought that he discredited his excuse by claiming to know which car was the kicker. Usually, the bugaboo of a kicker is that you don’t know which car it is, and its kicker behavior is erratic and unpredictable.
I asked an engineer if there were a way to determine which car was the kicker if you had a kicker in your train. He said about the only possible way would be if there were fresh snow on the ground, you might see it first plume up under the kicker if a kicker dynamited the brakes.
At a propagation rate of around 900 ft. = 15 car-lengths or so per second, that would mean reading the data to within about 0.07 second or so to identify a particular car. Can the data really be ‘read’ easily with that fine a degree of resolution of what is actually a ‘wave’ phenonenon ?
Also, that would only work after the ‘kicker’ has done its dirty work - and if that’s out on the road, there’s still the long slog to replace a knuckle necessary, etc. It still seems to me it would be better to do a ‘hard’ test in the yard - esp. once the EOT is connected and ‘armed’ - to attempt to force the kicker to happen while the train is still there, where it’s easier to get to and there are more personnel around to help, etc.
- Paul North.
Some dynamiters blow every time and some don’t. Some only seem to blow when moving below 15mph.
One of my coworkers related a story. They were coming up on a control point that was held at stop against them. Their train had a dynamiter in it and it had stopped them a few times. The train make-up required the conductor to inspect the train everytime.
The engineer thought the red signal may be stop test. Before he had to set air, he called up the dispatcher. “Why are you holding us? We have a 9500 foot train with a dynamiter in it. The conductor’s had to walk it three times already.”
The signal cleared up about a minute later.
Jeff
Thanks, this has been a great thread. I knew triple valve was the answer to Boyd’s question even before Carl posted his first answer, but I didn’t know exactly why. The explanations above have been great for explaining how and why this is. Thank you, gentlemen.
Bruce