• Steam engine dynamic braking?

  • Discussion of steam locomotives from all manufacturers and railroads
Discussion of steam locomotives from all manufacturers and railroads

Moderators: slide rules, Typewriters

  by BobLI
 
When a steam locomotive is running downgrade, is it possible to let steam into the cylinders to suppress the downgrade momentum? Would this cause any damage to the cylinders if it was done? Or is it just brake shoe and retainers to keep the momentum in check?
  by Steffen
 
Well, I told the story once before.
Nikolaus Riggenbach, the founder of the cogwheel railroads for steep gradients found a dynamic brake for steam engines - and this is the first dynamic brake for all trains!

if the steam engine runs under pressure, the piston is pushed by the step from one side to the other. If you idle, the piston is still waving driven by the rods.
Most engines do not idle very good, even in mid gear, so all channels in the cylinder steam chest are closed by the valves.
Thus, idle systems were developed, like snifting valves or idle piston valves.

But, Riggenbach found, that if the engine was going from pull to idle, usually the piston primed air from the blast pipe of the chimney. Nikolaus found, that this air was dirty, causing the lubrication film on the cylinder inner liner to get damaged by increased wear and scratching effects of small cinder particles in the smoke box.
So he wanted to use the primed air by the piston to be compressed by the piston wave and exhausted, creating a huge brake effect. So he constructed a snifting tube and a switcher valve below the blast pipe. From the cab, the enginer shifted this valve, to cut of the steam chests from the exhaust to the aspiration pipe. Now Nikolaus Riggenbach constructed a valve at the main steam tube, which can be used as additional throttle, but this valve drained to the air, and on the end he set a silencer.
Now the engineer was able to use the brake.
On the cogwheel railroad the engine had to move to summit station usually under constant power output, there was no idle. But all the way back, the engine had to idle and brake the whole train on the downhill ride. Now, this was nit anymore a problem of the brakes, because the Riggenbach brake used now the downward momentum and created a brake power through the steam engine itself.
Tries, to do this with steam fails, because of water hammer and control problems, but with Riggenbachs invention, this was simple.
Downhill the engineer shifted, and the exhaust was cut off, the valves were connected to fresh air. The waving piston, moved by the cogwheel and the bars, aspirated air, the valves closed and the air was compressed in the cylinder. The valves opened at a given cut off, and the compressed air rushed into the main steam pipe backward return to the steam throttle. To prevent this valve from pressed open by the air, the second throttle valve was now opened, generating a backpressure and puffer to the cylinder - the air was now pushed through the throttle valve into the silencer and into free air. And this was now like a air pump.
Simply take a small bicycle pump and hold the outlet with your thumb - pump and you will find the brake effect, as you squeeze against your thumbs pressure...
This is now, what happens in the cylinder on each revolution and very good dynamic brake is given. Cogwheel railroads in Europe and some engines which regular run steep gradient lines got this brake.
The engineer was able to adjust the brake effect by the gears and the extra throttle valve to the silencers. If one enjoys the downhill ride on a cograilroad - the enginer and his fireman like this rest in duty and enjoy also the downhill ride, because if adjusted properly - no further action had to be done, the brake does nearly everything alone. Because if the engine runs faster, the revolutions increase and more air is pumped and compressed, the brake effect increases automatically. If the engine slows down, less air is pumped by the piston, the brake effect decreases and the engine speeds up again...

This is dynamic braking of steam engines... guess you should google about or take a ride on a swiss or austrian steam cograil... and watch how silent and powerfull these brakes work.
The onlyproblem is: You can't stop the engine, thus you only and get it very, very slow. To stop and hold, you still need a common brake, like a hand spindle brake or conventional air brakes, to keep the trains stop... but is you want to simply hold on speed, the Riggenbach does it downhill perfectly.
It uses nearly the same power as what is need to push the train to summit.

If you don't know it - get informations on this
  by Allen Hazen
 
Nothing to add here, but I'd like to thank Steffen for his contributions to this and several other threads! Steam locomotives lasted longer in regular service in a number of European countries than it did in the U.S., and Steffen's German perspective is very illuminating.
  by Steffen
 
Allen,
we al should never forget, that Germany, as many other countries in europe had an other focus on steam engines. Also, I would remember to the fact, that steam locomotive development after WW2 was on a dying branch. The rise of Diesel and electric traction made further development obsolet in the eyes of many person in responsibility.
We can remember, that bevor WW2 enough facts about the draught systems of Kylchap and Lemaître, same with Giesl have existed, as well as with water tubes and combustion chamber expansions or limitations. Also iron casting was highly developed, that main frames on weldet or riveted basis would not allways represent the state of technology. Also roller bearings and further feedwater development was still very good understood...
If we look in the development of steam locomotives after WW2 and their improvements, based on this know improvments, we will find, that with the exception of full welded boilers with combustion chambers nothing really was spread on a large scale basis. New build locomotives lack all those improvements, thus being often in power and efficiency compareable to the former locomotives - mostly as a consequence of the regulatories within the board of engineering in the federal railways of germany.
Thus, I am museal club railroader and often we struggle with those misconceptions done in the past, and now lead to some difficulties - difficulties also very viewable in service in the past, but: As more and more engines got replaced with Diesels and Electro locomotives, these things didn't count anymore.
I do not only act as fireman, we also serve in the shop.We do most maintainance at ourselfes, also many of the main repairs. So we have a gret insight into the technology and the "how to's" of the steam engines - and I personally watch over the borders.
I am a fan of the 4-8-4 US Steam locomotives, like the UP844 or the so called Niagara locomotives of the New York railroads... I am so interested in technical details, but usually: It seems, there is nothing!
We in Germany got loads on this, like material descriptions, boiler describtions, maintainace rules and repair guidelines. We use this for doing the maintainace and repairs, thus we depend on those drawings, descriptions and measurements. So we understand in the work in the shop, how the parts work and work together. For example how the steam pump for feedwater works, or how an injector is maintained and why.

So when I visit another steam railroad... I try allways to increase and exchange knowledge. Increase my own and learn from the others. So the Riggenbach counter pressure brake, as translated word by word from german name, I first encountered in Austria - on the famous cog railroad from Jenbach to Achensee. On the 160‰ ramp up to Achensee the engine goes at maxium power output.... but downhill, I watched engineer and fireman enjoying the sunny day, because the Riggenbach brake was in operation, so both had the time to watch and to chat, while only certain views on pressure gauges and temperature controls were need. It was amazing, that the brake itself was able to hold the train down, without any additional brake, and taking advantage of the same structures as on the climb. Thus there was no additiona wear, no additional duty, nor was there any additional work to do... simply, set the brake in operation, adjust it and let the machine do the rest... Only on the stops, they need to increase the brake force to slow down, and in the moment of very, very slow to turn the spindle of the handbrake to hold the train astop!
On restart, they simply turned the spindle, open in this way the hand brake and let the engine start to roll. On the desired downhill speed they adjusted the Riggenbach brake and again: It did the job on it's own.
The piston the rods and the cogwheel did the same job... now not driven by steam force - now driven by gravity and retarded by aspiring and compressing air in the cylinder.
If you want to see and hear, watch my you tube Video on:

http://www.youtube.com/watch?v=tAEx1ZckGAo

The second time I was in Austria, I visit the cograilway to Schafberg - which starts on St. Wolfgang at lake wolfgang. The 1992 by the swiss DLM AG biuld steam engines do a great job on the railway and push nearly three times the load on double speed as the old steam engines. Downhill again, the engineer only controls the speed by adjusting the compressed air pressure and the ride is smooth and relaxed. Also here:
For a stop, the engineer increases the retard of the Riggenbachbrake to maximum, the engine get nearly so slow that it's standing still, in this moment the hand brake is tied up by a spindle and the engine is hold with the train astop... Start: Open the handbrake, let the engine get rolling and adjust the Riggenbach brake by increasing the counter pressure and so increase the retard... after: Enjoy the downhill ride.
There is no real noise downhill, it's a silent sound of rushing steam and air...

On both trains, the fire wasn't maintained downhill. The Achensee railway did a resting fire in the firebox, just to keep the boiler alive. On Schafberg the oil burner was shut down and the boiler kept the pressure because of proper insulation to restart the oil burner on the climb tour again without more to do.

Try this on diesels... No one will shut down the diesel on downhill travel. Only the electros can go here, they switch from motor to generator and feed the power generated during the downhill ride into the main grid...

But, I anyone has something about US steam locos, espacially details: Please, remember me
  by BobLI
 
Steffan,

Thank you for all the great technical posts. The information you provide is amazing!
  by steamer69
 
The Mount Washington Cog steam locomotives use a system that I guess you could call dynamic brakes for the trip back down the mountain. It works on the principal of compressing air in the cylanders. Water and oil are added and a valve in the cab regulates the amount of air that is allowed to bypass directly through to atmosphere. If you would like more information I can dig it up for you. It's agreat system so that the breaking for the locomotive is all done this way.
  by Steffen
 
steamer69,
the system you refer is the Riggenbach brake...
  by jozer
 
I have an idea for a hybrid compressed air/steam locomotive that is based on the Riggenbach brake. When the locomotive is slowing down/going downhill a 3 or 4 stage piston air compressor would be engaged to the drive wheels. This would charge a spherical air tank that could hold up to 10,000 psig pressure. Both of these would be inside an insulated low pressure boiler. The heat of compression can produce steam at 15-20 psig. At this point a centrifugal compressor would also engage the drive wheels. This compressor would pump the low pressure steam into the main boiler. When the locomotive power is needed the air compressor would become a compound air engine drawing air from the air tank and heat from the low pressure boiler. It would stay engaged to the drive wheels as long as there is enough air pressure to keep it running.The low pressure boiler would get heat by being used as a steam condenser for the steam piston engines. This would recycle the heat of compression and then some. This would also save water.
  by GoranH
 
Hello guys! Many times I wondered if steam locomotives had a dynamic brake. It is interesting how Riggenbach invented the counter-pressure brake. I understand the principle of operation, the steam cylinder works as an air compressor. I'm interested in how the gear valve should have been set during dynamic braking, whether to the maximum charge level or the minimum? Is there a draft or scheme of Riggenbach brakes?
  by Pneudyne
 
There is a detailed treatment of the Riggenbach brake in the following ILE (Institution of Locomotive Engineers) paper:

“Dynamic braking of Steam, Diesel and Gas Turbine Locomotives”, by J.L. Koffman

ILE paper #505, 1951 September.

The section on the Riggenbach brake runs to around 14 pages, with charts, diagrams, performance curves, etc. I suspect that it would go some way to addressing your questions.

This paper is findable on the web, but might require some patient searching with various and sometimes non-obvious search parameters (what I refer to as “lateral” searching).


Cheers,
  by GoranH
 
Thank you for your reply! Is there a link somewhere for “Dynamic braking of Steam, Diesel and Gas Turbine Locomotives”, by J.L. Koffman? I can't find anything under that title.
  by Pneudyne
 
Unfortunately, I did not keep a record of where on the internet I found that paper. My experience is that such links tend not to be durable, so some time back I gave up keeping a list of sources. For items that are not easily found, about all one can do is periodic repeat searching until they do turn up.


Cheers,