Welcome to European Tribune. It's gone a bit quiet around here these days, but it's still going.
Great photos and article, as usual! Some of them look like those pictures you see in model railroading magazines, where there is a mountainous village with multiple trains all adjacent to each other.

Unrelated question: I read recently that one reason it takes freight trains so long to stop under emergency conditions is that the brakes are adjusted so that when the car is empty, full emergency braking will still not cause the wheels to lock and get flat spots. Is that really the case?

The ratio between full and empty on a coal gondola, for example, is about 6:1. (140 tons laden, 22 tons empty, for aluminum gondolas as used over here.) That would suggest that you only get roughly 15% of the potential braking effort when the cars are loaded. Seems pretty sub-optimal...

by asdf on Fri Aug 23rd, 2013 at 05:47:04 PM EST
I'm not entirely sure about the situation in the USA but in present-day Europe, this certainly isn't true.
  1. The pneumatic braking system of most wagons are equipped with so-called load-proportional valves which adjust the pressure and thus the braking effort relative to the car's total mass. Most of the rest is equipped with hand adjusters for the same purpose.
  2. The purpose of load-proportional braking isn't merely to avoid wheel slip, but also to avoid train ruptures due to uneven braking.
  3. AFAIK the reason freight trains take so long to stop is that the braking system is adjusted for a slow development of full braking force, to avoid train ruptures and large longitudinal forces resulting from one end of the train already being fully braked while another end is still rolling freely. That's because in long trains, due to the relatively low speed of the propagation of the pressure drop in the main brake pipe, it takes a substantial time for all brakes to activate. In recent times however, heavy-haul railways (who run the longest trains) started to equip their rolling stock with electronically controlled pneumatic (ECP) brakes, so faster braking is possible.

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Sat Aug 24th, 2013 at 02:15:55 AM EST
[ Parent ]
Some relevant numbers from UIC and EU standards:
  • minimum transmission speed (speed of the reaction of the brake cylinders to the drop in the pressure of the main brake pipe): 250 m/s;
  • brake cylinder filling times: 3-5 s in brake mode P (passenger), 18-30 s in brake mode G (freight)
  • maximum length of a train taken into account by the standards: 700 m in brake mode P, 1000 m in brake mode G (freight)
  • maximum number of unbraked cars in a train: 50%
  • maximum length of a group of unbraked cars within a train: 80 m

I should also note that ECP brakes are a new advanced development for freight trains (two-way digital communication along the train, no use of the main brake pipe); but for passenger trains, electropneumatic (ep) brakes (which still use air off a [second] brake pipe) have long been in use.

As for North America, I find wagons have empty/load braking, too. Trains are much longer, however. I couldn't find the prescribed brake cylinder filling time.

*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Sat Aug 24th, 2013 at 07:26:00 AM EST
[ Parent ]


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