there is a pressure drop in steam pipes depending mostly on the diameter of the pipe. largest value on the chart is 10 psi / 100 feet which doesn’t seem like is can be very significant considering the distances on a steam locomotive.
there could be a pressure drop between the boiler and piston considering the length of the boiler and any valves (throttle). There could also be a back pressure in exhausting steam from the piston between it and the stack which is a considerably smaller distance.
does anyone know the pipe diameters between the boiler and stack?
i’m especially curious about the exhaust back pressure as a funciton of cutoff.
There is no “pipe” between the boiler and the stack. I’ll bet locomotive designers envied the stationary plant boys since their job in calculating pipe/HP sizes probably seemed so much simpler. Another difference is that the dry pipe is inside the boiler as opposed to hanging in free-air as in so many stationary plants.
“Genreally” the dry-pipe, most were internal, a few were external, runs about 8 inches ID or thereabout. The NYC Niagara, if I recall correctly, had an oval-shaped dry pipe with slots milled in the top of it for steam admission since the boiler was so large clearances didn’t allow for a “traditional” dry-pipe OR even a steam dome.
Many locomotives were superheater equipped so you have to calculate the differences in the area of passages, the return bends in the superheater tubes, the type of throttle (lots of variables there) how the passages were cored into the steam chest and the exhaust passages then on to the type and size of the exhaust nozzle(s). For the relatively short distance the steam traveled it went through dozens of twists and turns before exiting the stack.
Again, there are volumes of data written about various designs of steam distribution related to locomotives. One book I highly recommend which would be helpful in your quest to better understand the intricacies of locom
i’m trying to understand the effect of cutoff on drawbar force.
i’ve read that cutoff is reduced (reverser moved toward center) when acceleration starts decreasing as speed increases. Presumably, speed will be limited w/o reducing cutoff
i believe this is caused by the combination of the reduction of steam pressure from the boiler to the piston due to the volume of steam and the restriction of piping and the increase in exhaust pressure.
presumably increasing cutoff, which reduces the volume of steam, will partially negate the presssure drop from the boiler as well as decrease the back pressure because there is less steam to exhaust.
just having some idea of what the pressure drops are would be insightful.
I received this book yesterday (took an entire day to arrive). It looks rather interesting. A sufficient number of photos to cover the evolution of the steam loco in the U.S. Some diagrams of the innerds, and simple graphs of the thermodynamics (entropy raises its ugly head again) and physics aspects but not over the top complication.
I think I will enjoy absorbing it, but will try to continue reading The Complete Book of North American Railroading (by Kevin EuDaly, et. al.) as it sat a good while before finally starting that one. The combo should be an interesting educational upgrade for me as I have never before actually read a whole book on railroading nor steam power, other than the Ambrose book on the Transcontinental RR.
I just received the second book I listed, which was just released a few weeks ago. The author, William L. Withuhn had passed away before the book went to print and I understand his wife had assisted in the completion of the book.
American Steam Locomotives: Design and Development, 1880-1960 is a very comprehensive study in 450 pages. Well worth the $25. I paid. The illistrations, while not exceptionally large, are much more clearly reproduced than those in the Lamb book.
I highly recommend this volume for any student of the development of the steam locomotive.
High-Wheeled Racers
More Wheels and Bigger Fireboxes
Vehicular Design for Horsepower
Big Wheels Turnin’: A History of Counterbalancing
Innovation and Risk in Design: From Compound Cylinders to Superheating
Superheating: Design and Risk
Francis Cole and his Triumph of Empirical Science
Locomotive Safety Regulation: The Locomotive Inspection Act of 1911 and the Nationwide Shopmen’s Strike of 1922
Not to be nasty but,I’ll bet if both my Grandfathers,and one uncle was still alive they would be laughing.
As a child I use to ask many questions about steam locomotives and all three agreed as long as the fireman maintain a good fire he didn’t worry about anything other then the next signal, employee time table and 19 order. You see if the their fireman could maintain a good fire all was well.
The biggest issue in the steam years was a lot of slate in the coal,steam leaks and other mechanical issues that cause poor preformance of the engine and that spelled grief for the crew.
The mechanical engineering department studied questions like you are asking and usually came up with fool " operation improvements" that the majority of the engineers igored…
i think loco engineers appreciated the use of Walschaerts valve gear that replaced the Stephenson valve gear, and balancing the weight over the drivers to improve tractive effort.
most new technology is initially unrefined, then with understanding becomes more efficient (e.g. internal combustion engine).
Lindberg helped pilots in the pacific during WWII to fly more efficiently to significantly extend their fuel usage.
There’s the even more efficient Corliss valve gear, but the required linakge proved to be far too complex to implement on locomotives, though it was tried. It was a big part of stationary engines though. I have some good pictures I got last weekend at the Shreveport Water Works museum - it was the last operating steam powered public water pumping and treatment plant in the country when it shut down in 1980, and is now a national Historical Landmark. The two main high side pumps, a Worthington and an Allis Chalmers, are still in place, the Worthington is rigged up to operate with an electric motor turning the flywheel so you can see all the motion. I have pictures and video in my phone from it, amazing stuff. Those were installed in the 30’s and were used til teh end. There’s still an older one in place that was used prior to the ‘new’ ones being installed. The palce was originally built in 1897, and a few years later they added filtering and chemical treatment of the water, becoming one of only 10 cities in the entire country that provided filtered and treated water. The docent when I was there was very knowledgeable about steam engines, at least the stationary types.
I quite agree. It is interesting how steam, diesel, automobile and even airborne (prop, then jet) systems have been at first, revolutionary, then evolved. Quite a trip from the intitial steam stationary devices to the first steam locos to the later generation steam locos.
Not to ignore the point made above that the engineers and air pilots, on given equipment at a certain stage, were able to play with the given system at hand, which the design engineers had offerred at the time during the overall evolution curve. But each evolutionary step, including failures overcome, became significant.
Here are three .pdf articles that may be helpful in your research. These deal with the design and development of the New York Central Niagara which, by some industry standards, would be considered the crowning achievement of locomotive design.
Finally the road tests. Much of this data was gathered first-hand by the authors of these articles. Their notes and observations are invaluable to the student of steam locomotive design and operation.
The author suggests downloading the article and reading it as an Adobe document as the web browser view is not as sharp or easy to read. There were generously provided by the New York Central Historical Society, a very valuable organization to the railroad historian.
Normal ‘revealed wisdom’ is to get the throttle fully open as quick as possible (thereby reducing the flow restrictions in the intake tract, the items of concern to you, to a minimum) and then ‘drive on the reverser’, adjusting the cutoff to produce the desired degree of acceleration or speed.
I think you don’t understand exactly what cutoff is, or what it does. Reading up on link gears and valves, with specific reference to long-lap, long-travel valve gear (a la Churchward) will get you a long way toward seeing what the important characteristics (and periods within the stroke of the piston) are.
The point of cutoff is to allow the cylinder to extract the maximum amount of energy (heat, producing pressure) from the steam, while minimizing effects like compression or back pressure. This is entirely a function of valve modulation; while there can be flow-related restrictions in the inlet tract (as described in a couple of earlier posts here) their effect is only to change the observed steam pressure at the valves; the 85% correction factor in classical PLAN horsepower calculations is there in part for this reason.
Cutoff is an INTENTIONAL modulation, and the only real ‘problems’ with it are related to the SHM nature of typical link gear, which requires the timing and duration of exhaust events be related to inlet over the range of rotational speeds. “Better” gears (like the Franklin Systems) allow exhaust timing and duration to vary relative to inlet, with some inherent overhead cost due to tortuous steam passages; the practice of providing additional exhaust relief valves in uniflow engines is another example.
[quote]
Presumably increasing cutoff, which reduces the volum
Steam engineers had two things in common…They started as fireman and knew their iron steeds and from that experience knew what their engines could do far better then the fat cats that sit in office chairs…
Today’s engineers can be replaced by a computer. Crewless train are in the furture. A sad future if you ask me.
BTW.That Chauffeur did a good job and had the assembly shouting for joy and throwing books in the air until a student with big horn rim glasses and books under each arm asked a fool question… And we know the Chauffeur turn the tables on that student with he said my Chauffeur sitting in th
