That’s a complex story - lots has been written about it , lots of it is plain rubbish .
Even professional engineers of steam locomotive builders and railroads often seem to have had but rather limited understanding of what really can be obtained by compounding , what it’s for and what it takes to make it work . Occasionally , even today there are examples of people springing up exposing but fantastic ignorance when happily offering what seemingly they believe should be new relevations .
Maybe you could help me with this…why can’t the steam, once its done its work in the cylinder, be routed back to the boiler for reheating instead of being disipated to the atmosphere? This would be a closed loop where the steam would be reheated and reused. So far I’m told that it would be impossible to get the low pressure used steam back into the boiler where the pressure is higher.
Marine steam engines (on ocean-going vessels anyway) operated with condensers almost from the very beginning, salt water being absolutely the last thing you want in a boiler. Exhaust steam was condensed, then routed back into the boilers. Boiler pressure is just way too high to get the used steam back in in an uncondensed state.
By the way, anyone ever hear the old firemans saying? “If you wouldn’t drink it, don’t put it in the tender!”
Oh, and so no-one gets the wrong impression, I never said compounding and speed were mutually exclusive! I’m well aware of Vauclains, DeGlehns, and Chapelons compounds. A compound MALLET wasn’t a speedster on account of the difficulty of balancing those massive cylinders and assorted running gear behind the pilot.
How do you stop the high-pressure steam in the boiler from flowing out through the pipe you intend to use to bring the low pressure steam back into the boiler?
What you are describing is similar closed cycle gas turbine using steam as the working fluid instead of air or some other gas. The spent steam would have to be compressed before it could heated again and that compression takes a lot of energy - typical figures for a gas turbine is that ~75% of the power produced by the turbine is used in the compressor.
Condensed steam (liquid water) is much less energy intensive to pump up to high pressure than a gas (it’s very dense and almost incompressible). The downside is that you do throw away a lot of energy in condensation.
I would also add that the gas turbine (which operates using the Brayton cycle), steam power plants (Rankine cycle), steam engines (Rankine cycle), Stirling engines (Stirling cycle), etc. are heat engines. All heat engines must reject heat to a low temperature reservoir. Thus, heat rejection to the atmosphere is necessary regardless of the working fluid, including pure steam. Note that heat rejection for open gas turbine cycles is accomplished by dumping the working fluid into the atmosphere.
I am curious as to just what the aveage railfan considers “SPEEDY”, because it seems to me that most every railfan thinks that every train on every line has the track structure and grades to run 100+ mph whenever they want. So, is 30mph speedy? What about 40mph or 50mph? I think if you could do the research, you would find that trains yard board to yard board times averaged much less than even 20mph nationwide!
But back to Firelock76’s remark;
Why other roads didn’t persue developement of the compound mallet like the N&W did with their Y class, I have no idea. However as a former N&W steam engineer related to me, “You didn’t want to run the Y6’s much over 63mph. After that they started getting a little shakey”. Now, is that “balancing those massive cylinders and assorted running gear” enough?
I know we’ve had speed discussions in the past, and what it really boils down to is application to the circumstances.
Certainly not every train was expected to run near the 100mph mark, very few were in fact, it gets down to the application. If a Y6 on the N&W wasn’t meant to run any faster than say, 40 to 50 miles per hour, or frequently slower, that was OK, coal isn’t going to spoil if it doesn’t get to market yesterday. On the other hand, the Erie grabbed a lot of perishable freight business when they started running Berkshires that were comfortable running over the 50 mph mark. See where I’m going with this?
And passenger use? A passenger wants to get where he’s going quickly, that was the original attraction of the railroads to begin with, so for passenger use you’re going to need a, well for lack of a better term, “speedster”. It was true in 1840 and it’s true now.
And OK, if the N&W designers were good enough to get the Y6 to run at up to 63mph reliably, well good for them! It only confirms what geniuses they were. If other 'roads didn’t want to follow N&W’s lead on this I’m sure they had their reasons, some good, maybe some not so good. Personally, I think a lot of locomotive builders were secretly jealous, maybe insanely so, that those “hillbillies” down in Roanoke were better at the craft than they were!
Therein lies another big misconception about the N&W, They didn’t haul only coal. There was plenty of merchandise freight to be hauled too. And the workhorse Y class handled its share.
I wasn’t raggin’ on you.
Just stating the fact that there are many misconceptions out there that just don’t seem to go away. Like, the UP Big Boy was the biggest and best loco ever made, et al.
It wouldn’t work because the boiler is a pressure vessel. Any steam leaving the boiler is going to lose pressure as it goes through the pipes. The pressure is highest right when it leaves the throttle valve. After that it is all downhill from there. By the time it leaves the cylinders it has lost much of it’s pressure which is why mallets had to have a considerably larger piston for the second expansion cycle.
You simply couldn’t put 90 psi of steam pressure back into a 200 psi boiler. You couldn’t even put 200 psi into a 200 psi boiler. You would have to raise it to probably 205 or 210 psi to inject it into the boiler.
All this talk about steam sure makes me wonder what we would have seen if steam could have lived another 10 years or so. Was there ever a locomotive that was built that had a second steam locomotive behind it, which was only serving as a auxiliary boiler to supply steam to the primary locomotive? Has this ever been tried? You would need a steam pipe connecting the two locomotives but it would give you a unlimited steam supply as it would be basically two boilers providing steam for one locomotive.
Wait , wait , don’t - just ask = J = ! To de-crush you :
Big Boy was the one locomotive type with the largest number of axles between couplers , i e engine plus tender , of any steam locomotive on earth , Mallet or single frame concept , namely 19 . However ‘he’ wasn’t the longest steamer between couplers - this was long tall Sally-One , PRR 6100 . BB also wasn’t the one with the heftiest down thrust on rails , that was the Lima 2-6-6-6 BigFoot , exactly the Virginian RR version which was a little heftier than the previously built Carbon&Oxide version . As concerns applicable tractive effort it makes little difference in principle if you have - to simplify ! - 2 x 4 axles loaded at 30 tons each or 2 x 3 axles loaded at 40 tons each .
Since the ALCO Boys scaled at some 32 tons while the Lima Virgins kept ‘diet’ just below 40 tons per driven axle , you might want to suggest the Boys could grind some extra effort onto ramp rails , yet the Virchesty Halleygenny had an extra stamina for speed with a long train running because of ‘her’ large and deep firebox of unhampered proportions behind the drivers , rather than above them , which allowed to much better suit combustion . Another question if Lima plain nozzle double chimney draughting was up to Jabelman’s 2x4 nozzle double chimney design which again was far from perfect and certainly no match for an equivalent Kylchap design if properly executed .
The longer articulated chassis didn’t help the UP-Boys , at least not with conventional boiler design as it was then used in standard type steam locomotives in the US in the 1940s with basic decisions even such as between A type and E type superheater concepts still unresolved . The earlier Triplex types
If you routed the spent steam back to the boiler, then how would you maintain draft thru the flues? A problem with steam locomotives was that you had to expend that final bit of energy forcing the flue gases thru the petticoat and up the stack, where, of course, it’s gone. The exception was with the condensing engines used in South Africa and other desert climes - but then, how do THEY work?
Dear, you might consider a tad less stylized writing; it gets a bit murky sometimes. But charming.
As for the N & W’s steam program, if you look it “deep in the eyes”, you really DO find that the diesel’s advantages are, [alas!] overwhelming. But let me add another, seldom mentioned reason to dieselize:
If you were a successful steam-powered railroad who wanted to expand your territory by buying a small but equally successful regional railroad, if you went to your financial backers to secure the funds necessary for the transaction, then might they not demand COLLATERAL for their financial aid?? And what can you offer as collateral - a clutch of steam engines, along with immoveable coaling towers and water cranes, plus machine facilities tailored to maintenance of steam engines?
WHAT THE HELL GOOD IS THAT if you default on your loan, and you have to break up the railroad? What are all the other railroads, who have already dieselised, going to do with your steam-powered assets?
Face it, your little toy steam engines, no matter how efficient, are WORTHLESS to anyone but YOU.
And so, if you want to be a “player”, you have to KEEP UP - if everyone else dieselizes, the YOU must dieselize - unless you wish to have your motive power assets regarded as quaint and worthless.
For those who feel the need for steam, the book N & W: The Giant of Steam, By Colonel Lewis Ingles Jeffries, ISBN-10: 087108547X, goes into the details of simple vs. compound on the N&W. The Colonel does a great deep dive into what drove the N & W to invest not only in the hardware, but also the support systems with clear economic goals in mind. Such as reduced water and coal stops on the main-line, getting 100% availability of a 0-8-0 switcher per shift without having to stop for either. The only down size of the book is to so little was saved, such as the last built steamer (an 0-8-0) or a class Y for the future generations to see what magic art Roanoke made out of steel.
How do you maintain the draft on a condensing locomotive? With the blower, which then runs all the time, and not just to get steam up before you begin moving. Hmm–if the blower is powered by steam, is its exhaust directed through the smokebox?