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pressure drop between boiler and piston and piston and stack

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pressure drop between boiler and piston and piston and stack
Posted by gregc on Tuesday, March 19, 2019 9:04 AM

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.

greg - Philadelphia & Reading / Reading

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Posted by selector on Tuesday, March 19, 2019 4:57 PM

http://cs.trains.com/trn/f/740/t/189535.aspx?page=1

This thread should keep you busy for a while.  Big Smile 

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Posted by gmpullman on Tuesday, March 19, 2019 5:28 PM

gregc
does anyone know the pipe diameters between the boiler and stack?

Herein lies the rub...

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.

 Boiler_delivery by Edmund, on Flickr

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.

 Boiler_delivery_a1 by Edmund, on Flickr

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 locomotive design is Perfecting the American Steam Locomotive by J. Parker Lamb. There are many others but this one covers some concepts of "what-if?"

https://www.amazon.com/Perfecting-American-Locomotive-Railroads-Present/dp/0253342198

 

This book is recent and also contains valuable information that may help sate your thirst for knowledge:

https://www.amazon.com/American-Steam-Locomotives-Development-1880-1960/dp/0253039339/ref=pd_lpo_sbs_14_t_1?_encoding=UTF8&psc=1&refRID=FQX2NF857NY40GTPPVD2

 

Can you pinpoint an era in regards to your questions? There is a huge difference in the "design evolution" between, say a 4-4-0 Atlantic from 1905 to something like a PRR T1 or NYC Niagara.

gregc
i'm especially curious about the exhaust back pressure as a funciton of cutoff.

 Boiler_delivery_0002 by Edmund, on Flickr

 

 Hope that helps, Ed

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Posted by gregc on Thursday, March 21, 2019 12:53 AM

gmpullman
Can you pinpoint an era in regards to your questions?

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.

greg - Philadelphia & Reading / Reading

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Posted by peahrens on Friday, March 22, 2019 9:05 AM

gmpullman
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 locomotive design is Perfecting the American Steam Locomotive by J. Parker Lamb. There are many others but this one covers some concepts of "what-if?" https://www.amazon.com/Perfecting-American-Locomotive-Railroads-Present/dp/0253342198

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.

Paul

Modeling HO with a transition era UP bent

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Posted by gmpullman on Friday, March 22, 2019 5:35 PM

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.

1. High-Wheeled Racers

2. More Wheels and Bigger Fireboxes

3. Vehicular Design for Horsepower

4. Big Wheels Turnin': A History of Counterbalancing

5. Innovation and Risk in Design: From Compound Cylinders to Superheating

6. Superheating: Design and Risk

7. Francis Cole and his Triumph of Empirical Science

8. Locomotive Safety Regulation: The Locomotive Inspection Act of 1911 and the Nationwide Shopmen's Strike of 1922

9. Leadership in Industrial Research

10. Federal Takeover: Engineering and Politics -The U.S. Railroad Administration, 1917-1920

11. The Formative Contest

12. The Steam Locomotive's Final Form - The Hudson

13. The Steam Locomotive's Final Form - The Texas

14. The Steam Locomotive's Final Form - The Hudson - Part 2

15. The Steam Locomotive's Final Form - The Northern

16. Giants in the Earth

17. Counterpoint: Why the Diesel?

18. "Big Boy" and Allegheny: The Most Powerful of All

19. The T1 and Poppet Valves: The Last Important Innovation

20. The "Big Three" of the Norfolk & Western

21. Resisting the Revolution

22. Industrial Beauty and the Beholder

 

https://www.amazon.com/gp/product/0253039339/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

The specific questions posed by the OP are addressed by the author in the last pages of chapter one of this book. Further study of the "Cole Ratios" developed by Alco's chief engineer in 1914 would provide additional information.

Chapter 7 further studies many of the locomotive advancements of Francis J. Cole and, in particular, the application of his designs on "Alco 50000" which was built as a test-bed and demonstration of Cole's designs.

Cheers, Ed

 

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Posted by BRAKIE on Friday, March 22, 2019 10:01 PM

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...

 

Larry

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“Shut one’s eyes tight or open one’s arms wide, either way, one’s a fool.” Flemeth-the witch of the Wilds.
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Posted by gregc on Saturday, March 23, 2019 12:20 AM

BRAKIE
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.

greg - Philadelphia & Reading / Reading

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Posted by rrinker on Saturday, March 23, 2019 1:49 PM

 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. 

                                  --Randy


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by gmpullman on Saturday, March 23, 2019 6:40 PM

rrinker
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.

The PRR, Santa Fe, and others, experimented with several poppet and rotary cam systems of steam distribution.

 PRR_poppet_K4-5399 by Edmund, on Flickr

This K4 was fitted with an inside rotary drive shaft with the operating gearbox on the pilot:

 PRR_poppet_K4 by Edmund, on Flickr

A few others were tested with the Caprotti, or Franklin licenced rotary cam poppet valve arrangement.

 Franklin_patent_0003 by Edmund, on Flickr

 Franklin_patent_0002 by Edmund, on Flickr

As you point out, it really wasn't suited for railroad applications.

Good Luck, Ed

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Posted by peahrens on Saturday, March 23, 2019 9:28 PM

gregc
most new technology is initially unrefined, then with understanding becomes more efficient (e.g. internal combustion engine).

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.

Paul

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Posted by gmpullman on Monday, March 25, 2019 1:02 AM

Greg,

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.

https://nycshs.files.wordpress.com/2015/01/the-niagara-story.pdf

and Part II

https://nycshs.files.wordpress.com/2016/01/niagara21.pdf

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.

https://nycshs.files.wordpress.com/2014/07/roadtestingniagaras.pdf

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.

https://nycshs.org/

 

[edit] Another valuable source for data are the I.C.S. "Blue-Book" courses. Many of these books have been scanned and are available here:

 http://www.icsarchive.org/icsarchive-org/bb/

 

This one has tables describing the properties of saturated and superheated steam that you may find helpful:

{scroll down to part II}

http://www.icsarchive.org/icsarchive-org/bb/ics_bb_510c_locomotive_management.pdf

 

Hope that helps, Ed

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Posted by Overmod on Sunday, March 31, 2019 8:41 AM

gregc
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

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.  

Presumably increasing cutoff, which reduces the volume of steam, will partially negate the presssure drop from the boiler...

As I keep saying in other threads, we need a better term for changing cutoff: does 'increasing cutoff' mean shortening or lengthening it?  Presumably the former.

It's not so much that cutoff 'negates' the pressure drop from superheater to valves as it works with whatever pressure and mass-flow conditions exist at the valve inlets.  If that pressure should be a few psi lower than "usual" (say, due to colder weather conditions) the engineer will move the reverser a little differently to get the intended effect.  (That will still likely be the most efficient use of the steam, btw.)

... as well as decrease the back pressure because there is less steam to exhaust.

Yes, but there are two things involved here when expansion in the cylinder is optimized, remembering that with Walschaerts and piston valves the stroke distance to release is fixed.  One is that with expanding steam the pressure goes down; the other is that with earlier cutoff there is less steam mass to be passed out the sometimes-restricted exhaust tract and nozzle.  The latter becomes important because of the distressing tendency of steam to expand in volume when pressure is relieved: higher mass flow chokes the exhaust more quickly and increases effective back pressure that prevents the cylinder from exhausting fully in the time the valve gear 'meters' the exhaust port area open.  Residual steam in the cylinder will increase compression, perhaps well above nominal boiler pressure.  See 'Okadee'.

just having some idea of what the pressure drops are would be insightful.

There is not much I can add.  PRR did some tests on this in the early years of the test plant, but I don't have either the series or the reference to give you.  Any good technical discussion of Chapelon's 'improvements' in internal streamlining will give you a handle on what was improved, and from that you could probably back-translate to get some idea of the unimproved restriction and consequent pressure drop relative to steam demand.  (IIRC there are curves on this in La Locomotive a Vapeur, but I don't think they all made it into the translated 1952 edition.)

To paraphrase David Wardale, it's far more important to look at the losses associated with the valves and cutoff system than at any flow losses in the header and inlet tracting.  A principal effect of the long-travel valve with adequate lap is that the steam edge is moving quickly by the time it starts opening the port, meaning a much larger area is exposed to steam flow in a shorter time.  This in turn means that a larger mass of steam can enter the cylinder before admission is cut off and expansive working begins at high speed.  Effects like this are important to gauge and consider.

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Posted by BigJim on Sunday, March 31, 2019 5:48 PM

BRAKIE
Not to be nasty but,I'll bet if both my Grandfathers,and one uncle was still alive they would be laughing.


And Jerry Clower has a Chauffeur for you! Wink

.

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Posted by gmpullman on Tuesday, April 09, 2019 2:32 PM

gregc
i'm especially curious about the exhaust back pressure as a funciton of cutoff.

 

Interesting reading from results of the Test Plant at PRR's Altoona Works:

 

https://tinyurl.com/y2a38m7t

 

You can follow this conversation at the Trains Magazine site which may be relative to your search:

http://cs.trains.com/trn/f/740/t/189535.aspx

You may find better and more specific information there [Trains Forum > Steam and Preservation] than here in a model railroad forum.

[edit] I see this is the same link Selector posted above. I'll assume the OP didn't bother to read through it.


 

Here is a Google Book Review of the previously mentioned William Withuhn book Americsan Steam Locomotives:

https://tinyurl.com/yyohbo22


 

 

 

Good Luck, Ed

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Posted by gregc on Tuesday, April 09, 2019 3:54 PM

gmpullman
You can follow this conversation at the Trains Magazine site which may be relative to your search:

http://cs.trains.com/trn/f/740/t/189535.aspx

[edit] I see this is the same link Selector posted above. I'll assume the OP didn't bother to read through it.

i did read through and have exchanged numerous emails with the author

greg - Philadelphia & Reading / Reading

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Posted by gmpullman on Tuesday, April 09, 2019 4:18 PM

gregc
i did read through and have exchanged numerous emails with the author

Ok, that should give you what you need! Glad to hear Big Smile

Cheers, Ed

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Posted by BRAKIE on Tuesday, April 09, 2019 8:59 PM

BigJim

 

 
BRAKIE
Not to be nasty but,I'll bet if both my Grandfathers,and one uncle was still alive they would be laughing.

 


And Jerry Clower has a Chauffeur for you! Wink

 

 

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 the back can even answer that question.. 

Yes,I'm a big Jerry Clower fan.

Larry

SSRy

Conductor

“Shut one’s eyes tight or open one’s arms wide, either way, one’s a fool.” Flemeth-the witch of the Wilds.

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