Great American articulated steam engines

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Posted by feltonhill on Sunday, May 16, 2010 9:56 AM

Maybe N&W thought syphons weren't worth the extra installation and maintenance costs compared to circulators.  There's a lot of welding on the top part of a syphon, and they're in the middle of a high stress environment, thermally and physically.

The A's DHS excluding circulators is 530 SF; the EM-1 is 545 SF excluding syphons, 3% more than the A.  This seems to indicate that the firebox volumes may not be that much different.  Arch tubes make up 10% of the total Class A DHS; the EM-1's syphons make up 28%.

So, I still have to wonder - does a square foot of syphon/circulator transmit the same amount of heat as a square foot of crown and side sheets?  It seems that it would take a certain amount of time for the hot metal to transfer heat to the water passing through.  Sort of like dipping your finger in hot water.  If you're quick enough, you won't get burned.  With a dwell time of 3-4 seconds, there may be a different result!

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Posted by GP40-2 on Sunday, May 16, 2010 8:58 PM
feltonhill
So, I still have to wonder - does a square foot of syphon/circulator transmit the same amount of heat as a square foot of crown and side sheets?  It seems that it would take a certain amount of time for the hot metal to transfer heat to the water passing through.  Sort of like dipping your finger in hot water.  If you're quick enough, you won't get burned.  With a dwell time of 3-4 seconds, there may be a different result!

That's a good question that for a steam locomotive might be hard to answer in this day and age. I would think that a well designed and integrated thermic syphon(s) were be quite efficient in absorbing radiative heat. Whether or not they are equal to the crown sheet, I have no idea. They would be far better that any indirect convective surface area.

The builders had no choice at that point other than to add syphons / circulators to the design. These large locomotives were at the limit of useful size. The EM1 was only 6 feet shorter than a Big Boy, and most of that was due to a smaller, shorter 6 axle tender. There simply wasn't any more room to physically enlarge the firebox/combustion chamber. To give the EM1 a total of 760 sq.ft. direct heating surface, the additional surface had to come from internal sources (the syphons and arch tubes). The N&W faced the same size constraints with the Class A. The only other option was a full water tube boiler, which was shown to be too fragile in the railroad environment.

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Posted by erikem on Sunday, May 16, 2010 10:36 PM

feltonhill

So, I still have to wonder - does a square foot of syphon/circulator transmit the same amount of heat as a square foot of crown and side sheets?  It seems that it would take a certain amount of time for the hot metal to transfer heat to the water passing through.  Sort of like dipping your finger in hot water.  If you're quick enough, you won't get burned.  With a dwell time of 3-4 seconds, there may be a different result!

 

The first key issue here is heat transfer from the flame/combustion gases to the steel in the syphon, circulator , side sheet or crown sheet - the water can usually be assumed to absorb all the heat absorbed by the steel, one exception is when the temperature of the steel gets so hot as to cause film boiling, e.g. when a crown sheet becomes temporarily uncovered.

The second key issue is that most of the heat transfer from the steel to water is due to localized boiling (nucleate boiling). The faster flow in a circulator or syphon will speed up the process of the seam bubbles moving from the spot they were formed to the top of the liquid surface in the boiler and then to the steam dome.

- Erik

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Posted by J.Rob on Sunday, August 01, 2010 2:24 PM

Page 195 and 196 0f "Allegheny Lima's Finest", a caption reads"The highest d.b.h.p. recorded for a C&O Allegheny was 7498 at 46 mph with over 14,000 tons: the highest sustained drawbar horsepower(on the same trip) was 7,375. This performance was in fairly flat territory in South-central Ohio." Further in the caption "Maximum drawbar horse power developed is available for both the N&W A and the C&O H-8, with each road's own dynamometer car - N&W's built in 1920 and C&O's built in 1929.  The only drawbar horse power figures for the "A" ever published were obtained in 1936 and were "made with one of these locomotives while handling a merchandise train where the tonnage was relatively low and the speed high." On level track the "A" tested developed "over 6000 horsepower at speeds from 32 to 57 mph, with a maximum of 6300 hp at 45 mph."

I hope that sheds some light on the debate. I recommend the book very strongly to anyone looking for info regarding the big three locomotives in question. Some other things to consider are the numbers of the locomotives themselves, and how many other roads used the type. In another section of the book a discussion is made as to which of the designs had the most room for additional gains and clearly the Allegheny could have increased power out put considerably where as the other two were nearly at the limit for the technology of the time. Also the "A" a fine locomotive was not chosen over the C&O's 2-10-4 when a comparison between the 2 was done by the Pennsy which then built 125 of the texas type to use during WWII.

Factor of adhesion is also quite good for the H-8 as on one occasion an apparent mistake when doubling a train from two yard tracks resulted in an H-8 stalling on the Limeville bridge due to tonnage greatly exceeding it's capacity. Locomotive did not slip just stalled.

Some day I will make it to one of the museums that have one of the H-8s on display and get to see one in person. I have seen the big boy on display in Dallas and it is quite impressive.

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Posted by GP40-2 on Sunday, August 01, 2010 7:28 PM
J.Rob,

The problem with many of these types of books, is the author makes a statement, but does not link it to a specific, verifiable road test of the locomotive. As Timz and feltonhill has pointed out, many of these tests can not be compared. What is the railroad's definition of "sustained" HP? Was the drawbar readings corrected for acceleration and/or deceleration? Are were talking about indicated or drawbar HP? Was the locomotive fired in a typical day-to-day economical operating fashion, or was it over fired just to see what it could do?

Without having a citation to a specific road test, and without knowing the specifics on how the test was conducted, it is impossible to verify such statements. On one hand, the author might be spot on. On the other hand, he could just be repeating what someone else told him, or just stating his opinion on the matter.
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Posted by BigJim on Monday, August 02, 2010 12:23 PM

UP 4-12-2

According to Huddleston, the USRA 2-6-6-2 was regarded, even during its era, as nearly a "failure" in comparison to the much more successful and powerful USRA heavy mallet 2-8-8-2.  Only 2 railroads bought them, and even though C&O built 10 late copies, they were primarily to replace worn-out locomotives on mine branch line service--where they were ideally suited.

It is my understanding that N&W borrowed one of the C&O 2-6-6-2's and they outperformed the N&W Y-1 & X-1. That convinced them to buy the 2-6-6-2. Which must not have been any disappointment at all since they owned so many of them and they lasted till the ending of steam on the N&W.

.

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Posted by JimValle on Wednesday, August 04, 2010 8:15 PM

To get back to the SP cab forwards just briefly, the rated tractive force of the last of the classes, AC-12,  was 124,000 according to Robert J Church who wrote the difinitive book on them.  I believe their claim to greatness lies in their being such a successful innovation and so well adapted to their purpose rather than their raw power output. One factor that stopped UP from converting more Big Boys to oil firing was the high rate of fuel consumption they experienced with the one engine they did convert.  " She just gulped it down" was how one engineman put it.  Apparently the coal fire with its thick bed of fuel over the grates had more staying power and stability.

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Posted by twhite on Friday, August 13, 2010 6:15 PM

Jim--

Actually, the AC-6 was the first of the Espee cab-forwards to have the TE increased to 124,000lbs from the earlier AC 4/5 4-8-8-2's at 116,000lbs.   The AC 6 was the last 'flat-faced' AC, but it was the first to have the 'talking' pumps built onto the smokebox front, and the newer style Worthington FWH.  Though it kept both the 'spoked' drivers and the Hicken semi-vanderbuilt tender of the two earlier AC classes, it was the true 'transitional' AC.  After the AC-6, all AC's were built to specifications of 124,000 lbs. TE, even the 'cab backward' AC-9 from Lima.  

Though almost every class of AC from Baldwin contained further and further improvements as far as locomotive design was concerned, the TE remained at 124,000 lbs., which was quite sufficient for SP.  From the AC-7 on, with the improved balance of the Baldwin disc drivers, they were also designed for 70mph maximum, and on some of the more level sections of the Espee's trackage, had no trouble achieving it. 

You're right, Church's book is superb.  Another very good book on the subject is George Harlan's THOSE AMAZING CAB-FORWARDS, first published in 1983.  I don't know whether or not it's still in print, but it's definitely worth searching for, IMO.  It has some excellent information on the early MC series 2-8-8-2 and the MM series 2 (later 4)-6-6-2's, also. 

Those incredible locomotives were part of my childhood up in Truckee, CA.  I have great memories of them.  Heck, until I was 10, I thought ALL articulateds ran cab-first, LOL!

Tom

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Posted by drumhead on Thursday, July 27, 2017 8:59 PM

feltonhill

 I found a lecture presented by Robert M. Pilcher 3/12/53, at that time Assistant Engineer of Tests for N&W.  He had this in his script:

 "Under unusual spot conditions dynamometer records a maximum sustained horsepower of 6300 at 45 mph."  [He did not specify boiler pressure for this reading, but other sources indicate that it was 275 psi.  No test report has been found yet]

 "In usual day to day operation, the dynamometer record indicates drawbar horsepower between 5200 and 5400 over long distances at speeds between 35 and 40 mph while handling 175 loaded trains over almost level track."

These figures occur frequently in N&W public statements and articles written in the 1940s-50s.

N@W class A  J  and Y6B had boiler pressures of 300 pounds at popoff during RR operation! PRRQ2 4464 duplexes on PRR tests on in house HP tests was almost 8000 horsepower, higest HP of any American steam locomotive except possibly the S2! The N@ W and the PRR designed and perfected their own locomotives for their own service needs, the class A was a very remarkable 6 coupled locomotive and produced more power TE than any challenger type built, the 6300 HP rating was also accurate under actual road performance!  

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