I have read that normal air brakes propagte at the speed of sound, which I think is supposed to be somewhere near 768 MPH. ECP is supposed to be near the speed of Light or 186000 MPS.
When all is applied, there are sti
Agreed. That would mean that an emergency application initiated only from the head end would take about eleven and a half seconds to travel the length of the train.
Figure half that for a simultaneous EOT dump, and then it depends on whether DPUs add any advantage.
An emergency application propogates at about 950 ft per second. The service rate is slower around 250 ft per second. If the lead consist is placed into emergency, the DP consist(s) will also go into emergency. Some engines are equipped to dump the EOT when the engineer places the automatic into emergency. Instructions are to toggle the EOT emergency switch anyway when placing the handle into the emergency position.
Jeff
Thanks for the clarification.
Velocity of propagation along a wire is often significantly less that the speed of light in a vacuum. My finger in the air guess for ECP control lines would be 70% of the speed of light in a vacuum. Having said that, there will likely be more of a delay in the electically controlled valves opening than it take the signal to reach the end of the train.
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Apologize for tghe serious eror in the casec of Megantic. Slow cleak. Would not have triggered ECB in any case.
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Speed vin wire significantly less than light? In any case, far, far faster than air-pre3ssure change in train-line.
For our purposes, signal through the wire will be virtually instantaneous. As Balt notes, though, it’s still air from the valve to the brake cylinders, and from that point, Newton is still valid.
What does that mean? Why is it significant? It sounds like it means there is significant time lost for the air flow; as in the case of the long process of a service application exhausting air from a mile of brake pipe through just the engineer’s control valve.
But with an “Emergency" application, how long would it take for a car brake valve to fully open, and the reservoir to equalize with the brake cylinder? A quarter-second?
Say you have a 200-car train with ECP. The 200 car valves open simultaneously (for all practical purpose). Then it takes just a split second for all 200 car brakes to fully set simultaneously with maximum force.
The point being made is that while ECP can improve train handling and allows for a faster response, it will still take a fair amount of time to stop 200 cars.
All true, but not immutable. High buff/draft forces come from having locomotives only on the head end. DPU changes the game - if you do it right. Also worth noting Roadrailers only good for 400,000# buff/draft.
Building for 6 mph collisions probably doesn’ require 800,000# buff/draft - sort of like slack run in, no?
Trainline current fed throttled though locomotive brake valve. Wide open trainline at higher pressure charges reservoirs much faster. Once you get rid of co-mingled power and control signal, you can do this.
All true. Not immutable. Clearly better yard track condition would be needed. Take a look at Machen yard in Hamburg Germany. They wheel out of the
So, existing systems have two parts to brake valve. An emergency portion and a service portion. As far as I know, existing ECP trials have only included service portion. Emergency from break in two, would still trigger emergency braking to “old fashioned” way.
I could see a “both/and” solution. Trainline rapidly to zero? Emergency braking and put the “word” out on the data trainline.
It’s important to remember that a lot of air brake technology requires the controls having to “tiptoe” around stability issues. The whole thing has been built and calibrated to:
a) react as fast as possible
while
b) not reacting to transients.
It is the rate of change of pressure that determines emergency versus service braking. The control valves are damped not to react to transients that come from pressure waves bouncing around and reflecting off surfaces in the trainline.
The feed valve on the locomotive is regulated not to allow high flow rates in order to keep things stable. Too fast and you could trigger valves in the train to do all sorts of nasty things, like UDE and stuck brakes.
It’s an outdated system. While pneumatic controls were pretty common in the analog days (Baldwin air throttles, anyone?) they all faded away by the 1970s. “Westinghouse” air brakes might be the last…
Damn. So, 0.00002 seconds for the signal to get to the EOT!
I would think an ECP system could build brake cylinder pressure faster than current system, because you’re not trying to do the dance to match brake pipe pressure. Transients on the brake cylinder pressure side of things that you’d get from dumping air in fast would likely give the control valve fits.
It would still take longer than 0.00002 seconds, though!
Gonna send you back to Physics class, too! Maximum braking force is coeff of friction x mass of car. Also, F=ma.
coeff of friction x m = F = m x a. m cancels out. max decelleration = coeff of friction. Doesn’t matter if 1 lb or 10,000 tons.
That is surprising news. Having ECP perform an emergency application “the old fashioned way,” I assume would require the old fashioned “triple valve and control/charging function of the old fashioned brake pipe. That would provide the quick acting function to trigger a car-to-car chain reaction that would sequentially dump the brake pipe under each car.
It doesn’t take long for the brakes to apply, but it’s not instantaneous. Air is still a fluid, flowing through pipes and hoses. And there is the mechanical portion of the system.
Even if it were instantaneous, there’s Newton.
Damn that Newton - Give him some figs.
Isn’t it amazing how quickly a bit or byte can be stopped versus over 100 tons of rail car assembled in 15K ton, 20K ton, 30K ton trains.
That’s exactly my point and was having a little fun with the difference in velocity of light in a vacuum as opposed to a cable. This has been very relevant in the work I’ve doing the last couple of years.
I’ve been wondering if installing the equivalent of a dynamic brake on each car migh be an even better way to go with the air brakes kept as back-ups. These could be set up to do a maximum power point tracking which would continuously try to find the braking effort that gives maximum electrical power output from the generators. One advantage is further reduction in brake wear and presumably less heating of the journal bearings. This, of course, is even more blue sky than ECP, but potenially could added on to cars equipped for ECP. Biggest problem is where to mount the generators on a three piece truck.
Generators are in pairs, hinged on slide pins like those for disc-brake calipers from the truck bolster, with a central pulley (probably for the Gates belts proposed for boosters in the '80s). There need to be Weller tensioners on both the top and bottom of the loop, otherwise the car will not ‘set up’ properly in one direction.
Obviously (to me) this is also the only practical solution to ‘autonomous’ drive. My suspicion is that both applications would have to be marketed and sold synergistically to make the idea worth anything practically.
I don’t follow you. The question was whether ECP brakes would let you design lighter freight cars. I still think that humping, kicking, and moving cars around in the yard with no air cut in will quickly put a lower limit on how much you can reduce the strength and tare weight of a car with ECP brakes. Does a Roadrailer have lower buff strength limits because it operates in a low-slack train, or because it never goes through the abuse of a classification yard?
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dpeltier
On the mainline, most contexts requiring restricted speed are either a.) solvable by the more-advanced train-control systems that are in the works, thanks to PTC, or b.) protecting a potential track defect such as a broken rail, where there is good reason to limit speeds anyways. In yards, 80-90% of all tracks are limited to 10 MPH by turnout size and track condition. And many movements within the yard don&#