Steam Dynamic Braking?

[CSX2057]

I'm not sure if the steam engineer ever did this. I'm testing out how many cars can a UP BB (IHH V1) pull on a 1.1% and 2.3% in Donner Pass. So far everything was looking good and now I'm noticing something. I'm passing Norden downgrade, did any engineers ever pulled the reverser in reverse and pull the regulator and acted as a dynamic braking? I read one article but I wasn't sure if that was true.

[GaryG]

I pretty certain that was a no-no! I think you would just lock the wheels even with a minimum throttle opening. I know it appears to work with our virtual steamers but in the real world physics appear to be "modeled" differently for some reason ;-)

GaryG

[BNSFdude]

It worked, but I've heard plenty of green hogs trying that back in their day and blowing the steam chest.

[CSX2057]

Here's what I found now which I didn't know they can do that. Its called: Countersteam brake

http://en.wikipedia.org/wiki/Countersteam_brake

[FourEightFour]

That is a big no no. BIG NO NO. Just NO

[CSX2057]

Ain't no point of yelling.

[philmoberg]

Actually, there were at least a couple of Swiss narrow gauge lines in the Alps that used this. It required a special valve that worked something like a snifter valve in reverse. This was used only on rack railway sections - at least in the examples I've heard of - so as not to risk slipping the driving wheels, which would have been disastrous when trying to hold a train on a steep grade. It appears this system was abandoned when power brakes became practical. IIRC there is one such example on display in the Verkehrshaus Schweiz, in Luzern, In which they sectioned the cylinder on one side to show how the steam passages for this very complicated system were integral to a single casting. The pattern maker had to have been a real genius: I'm not sure we'd have the expertise to make such a pattern these days, given the sort of work it would take to make the various cores. On top of all this, there were separate sets of cylinders for rack and adhesion propulsion so there was no possibility of using the special valve off the rack.

As a side note, at least with respect to North American operations, what typically happened on steep grades, once air brakes became common, was that a retainer valve was set on every fourth or fifth car before descending a heavy grade. What this would do is retain the brake application on cars so set, even when the engineer released the train brake. Of course, this required the entire train to be stopped at the top of the grade to set the retainers, and stopped again at the bottom to reverse the process. Crews and management alike were much happier when early DC electrification allowed them to use regenerative braking, which put the current back into the line. When diesel-electrics became practical, the designers drew the obvious conclusion and applied the same idea, only they had to discharge the energy as heat, since there was no electric line to put the power back into. Retainers didn't go away, but there were whole lot of railroaders who were happy they no longer had to routinely bother with them. Perhaps somebody who is more familiar with current freight car practice can comment as to whether they even have them anymore. I'd certainly be curious about it.

[buzz456]

Moving this to the Jungle.

[mapitts]

Both the N&W and the PRR used something called a Sniffter valve. Worked kind of like the Wikipedia post. The main thing you have to remember is that a steam locomotive cannot run with no steam going into the cylinders. The packing will seize so you have to have a small amount of steam for lubrication. If the timing is right with the reverser, valve and exhaust, you will get a small cushioning effect. Enough to slow a train, but not so much that you bend rods or break pistons. Too much and you blow out the steam chest or the valve gear.