A-2 Boiler details query

The boilers on the P&LE Berkshires (Alco's last steam locomotives) LOOK like those on the Niagaras. Some of this resemblance is due to purely cosmetic features: notably, the very flat smokebox front. But there seem to be deeper resemblances as well: most telling, perhaps, is that they have the same maximum diameter (100 inches). The grate area, 88 square feet, could have been obtained by using the same (8 foot) firebox width as the Niagara, but shortening the grate from 12.5 feet to 11 feet. (Grate dimensions in American steam locomotives seem almost always to be multiples of 1/2 foot. I'm not sure why this is so: perhaps design and construction was easier using standardized fire bars? For the historian it gives a helpful shortcut: given the grate area it is usually possible to make a decent guess as to its length and width!)

So, how deep were the similarities? Did they use the same sort of slotted pipe to collect dry steam? (Seems likely: certainly the boilers LOOK domeless.) Did they have combustion chambers, and if so how long? Did they have the same number and diameter of tubes and flues as the Niagaras?

I assume that these locomotives were written up in "Railway Mechanical Engineer" when they were new, but I've never seen any references, or for that matter, any decent drawings of these locomotives.

Hmmm.... I really should learn not to post without a reference book in front of me!

I'm not sure how I misremembered the grate area as 88 square feet! Alfred Bruce's "The Steam Locomotive" has a few dimensions of the A-2 in a photo caption: firebox 90.3 square feet, grate 96" by 135". Which itself is mysterious: I don't think I have ever seen another American steam locomotive described as having a grate of that length-- usually, as I mentioned in my previous post, grate widths and lengths are (to within a fraction of an inch) multiples of six inches, and this one is 11 feet 3 inches long.

Anyway, the caption also says there was a 42 inch combustion chamber, and that the tube length was 18 feet.

I'm still curious about the number and diameter of tubes and flues, and about the steam collection (Niagara-style slotted pipe or something else?). But so far everything is at least consistent with it being a shortened version of the Niagara boiler. (In shape: material might have been different. The Niagaras were built with an unusual alloy boiler, which very quickly started to show cracking: they were re-boilered early in their careers. The A-2, with a lower boiler pressure, and with no apparent effort to keep the weight of the design down, might have had boilers made from some more standard steel.)

I'm not sure what you mean by a 'good' drawing.
A dimensional drawing of the Niagara with cross-sections by Harold Geissel can be found in the Nov. 1946 Model Railroader. This drawing is reprinted in Alvin Stauffer's book, Steam Power of the New York Central System, Vol. 1.
A dimensional drawing of the P&LE A-2a with cross-sections by Al Armitage can be found in the March 1997 Mainline Modeler. This drawing is a 3-page foldout in 3/16"=1' scale.

NYC_Dave--
Thanks! I knew about the Niagara drawing (and think I can find another), but had forgotten that a drawing of the A-2 was published in recent times: will look for it.
As to what I mean by a "good drawing"... That's like defining pornography: I know it when I see it. (Grin!)
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Meanwhile... A bit more crow-eating for me. Grate lengths and widths divisible by 6 inches are more common than not in modern (post 1910 or so) American steam, but there are more exceptions than I realized. INCLUDING (this is deeply embarrassing for me: I *R*E*A*L*L*Y* should have checked before posting my first query!!!) the obvious design to compare with the A-2: the "standard modern Berkshire," the NKP/PM/WLE/C&O/RFP design: 135 inches long, 96 inches wide, 90.3 square feet of grate area. (So, in THIS regard at least, the A-2 is a "typical" late Berkshire.)
I have a few more thoughts-- the A-2 is more mysterious every time I look at it-- and will try to post tomorrow, after gathering my thoughts, and WITH my reference books at hand!
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Meanwhile, an additional question comes to mind: does anyone here know what type of superheater (Type A or Type E) the A-2 had?

The A-2's had a Exhaust Steam Injector instead of a feedwater heater(per Al Stafer's book,New York Central's Later Power 1910-1968
Pages 112-115)

Backshophoss--
Thanks! Will re-read the chapter in Stauffer to see if there are other details i have forgotten!
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Exhaust steam injector-- a.k.a. "poor man's feedwater heater." The A-2 (as I think Stauffer points out) was a weird combination of ultra-modern (e.g. the over-fire steam jets) and very old-fashioned.

Re: Niagara drawings
The drawing of the Niagara reproduced in Stauffer's "Steam Power of the New York Central System" (referred to by NYC Dave) is a fairly old "Model Railroader" drawing: I don't know what size it was originally published, but it looks as if it is a bit less detailed than some more recent drawings in model rail publications. The cross sections, alas, don't show internal boiler details!

There is also a drawing of the Niagara (specifically the prototype, S1a 6000) in the article published in "Railway Mechanical Engineer" (October 1945 issue, pp. 421-428) when the locomotive was new: this article was reprinted in "Train Shed Cyclopedia" # 56 (Newton K. Gregg, publisher, 1977). This is larger than the drawing reproduced in the Stauffer book: given the thickness of the lines relative to the total size, it looks as if it was originally drawn at a larger scale. The "Railway Mechanical Engineer" drawing is in a "semi X-ray" style, and shows constructional details (e.g. spring rigging, internal configuration of the smoke-box) that would not have been visible looking at the locomotive: the "Model Railroader" drawing, conversely, is "cleaner" in its portrayal of the external appearance of the locomotive. I'm very glad to have both in my possession!

The RME article also has a diagrammatic sketch of the boiler, showing major dimensions, location of the slotted dry pipe, water level in operating condition...

For comparison with figures for the A-2 (which I will post later): The Niagara boiler had 177 4" flues and 55 2.25" tubes, with a tube length of 19 feet (in locomotive 6000, which had a 92.5"combustion chamber: later Niagaras had 81.25" combustion chambers and correspondingly longer tubes/flues). Evaporative heating surface was 460 square feet for the firebox & combustion chamber, 57 square feet for arch tubes (total for firebox, therefore, 517 square feet) and 4,115 square feet for tubes and flues: total evaporative heating surface, 4,832 square feet. Test your knowledge of steam: can you tell which type of superheater was installed, given the 4" flues? (Grin!) Superheating surface was 1,997 square feet.

O.k., now for the A-2 boiler.
The A-2 had a very FAT boiler: the A-2 LOOKS like more of a hulking brute of a machine than, say, a Nickel Plate Berkshire. So it comes (i.e. it came to me) as a bit of a surprise that its heating surface is actually less than that of an NKP Berk! The difference, I think, is accounted for by the A-2 having a SHORTER boiler than the NKP 700: after all, if fits over a set of driving wheels that totals 2 feet less in length (69"-63" = 6", times four) than that of the NKP engine.

Anyway... Figures from Alfred Bruce's "The Steam Locomotive in America," photo captions from plate facing page 277(*).
NKP Berkshire (from the final, 1949, order): Tube length 19 feet (helpfully the same as on the prototype Niagara!), Evaporative heating surface 4,772 square feet (alas, not broken down into components), superheating surface 1,932 square feet.

A-2: tube length, 18 feet, Evaporative heating surface 4,292 square feet, superheating surface 1,877 square feet.

Now we can do some arithmetic. I think the results suggest an answer to my original question: the A-2 boiler's internal arrangements were probably similar to the Niagara's.
---Superheating surface is the easiest to use. The superheater elements were inside the flues, so, if the the type of superheater and the number of flues are the same, the superheating areas should be proportional to the tube lengths. And they are! (Well, almost: to within about 4 square feet.) The A-2's 1,877 square feet is very, very close to 18/19 of the Niagara's 1,997. So my (tentative) conclusion is that the A-2, like the Niagara, used Type E superheaters (did you guess that right when you read my last post?), and that they had the same number of flues packed into their equal-diameter boilers.
---Evaporative surface is harder to figure, since (a) I don't have a firebox vs tube/flue breakdown for the A-2 and (b) given the complex geometry of the firebox and combustion chamber I don't know how that component of E.H.S. area should vary with the length of the firebox and combustion chamber. BUT... It looks as if the heating surface area stated for the A-2 is at least in the right ballpark to be what you would get by shortening the Niagara's boiler by the known amounts (grate shortened from 150" to 135", comb. cham. from 92" to 42", barrel between tube sheets from 19' to 18') with no other changes.

(I have been fascinated by these unusual locomotives since I found out about them-- when I was in graduate school in Pittsburgh and, with the Penn Central, the B&O, and the P&LE to look at, first became a serious railroad enthusiast-- and will post more if I find out more. If anyone else knows more about them, I'd love to hear from you!)

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(*) Originally published by W.W. Norton in 1952: my copy is an apparently undated Bonanza Books reprint

You're right-- the A-2 had the same number of tubes and 4-inch flues as the S-1a, S-1b and S-2.

Thanks, Timz!
NOT as a challenge, but out of curiosity, where did you find that out?
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Tangential to A-2, but I noticed, looking at one of Alvin Stauffer's books last night, that one of the P&LE's heavy Pacifics had smoke consumers/ overfire jets (the row of cylinders along the side of the firebox) in a photo probably taken late in its career: it wouldn't have been built with them. Did the P&LE similarly modify other old steam? Anddid other parts of the New York Central system use these devices, or was it a P&LE idiosyncrasy. (Leading to the question of how independent P&LE' mechanical department was of the NYC's: did P&LE make major decisions -- like, maybe, that of ordering a low-drivered 2-8-4 drag engine in the late 1940s -- by itself, or would that have been a decision taken at the NYC headquarters?)
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Don't have time to write it up now, but I have had a few further thoughts: maybe tomorrow.

O.k., this is a bit tangential: not so much directly about the A-2 but more generally about the Niagara-style boiler (and what made the Niagaras great).

Look at the heating surface figures again: the Nickel Plate Berkshire has almost as much evaporative heating surface, and MORE superheating surface, than a Niagara. (Figures below, this time for the NKP S-class: their first, Alco-built, order of Berkshires.) What's going on? I mean, the NKP Berkshire was a big engine (weighing about 4% more than a NewYork Central L-4 Mohawk), but by no means as big as a Niagara: an NKP S weighed about 88% as much as the NYC S-1a.

Heating surface areas:
Evaporative, firebox: NKP S, 462 square feet, versus NYC S-1a, 517 square feet
Evap, Tubes & Flues: " 4,356 " " 4,115 "
Evaporative, total: " 4,818 " " 4,832 "
Superheating: " 2,243 " " 1,977 "
(Sources: for Niagara, the Railway mechanical Engineer article cited above; for NKP Berkshire the 1941 "Locomotive Cyclopedia" (facsimile reprint by Kalmbach, 1971), pp. 140-141.)

The only category in which the Niagara has more heating surface is in the firebox (which is, admittedly, important: more heat is transferred to the water in the boiler through a square foot of firebox wall than through a square foot of tube or flue). The Berkshire has significantly MORE tube and flue area than the Niagara, even though both engines have a 19 foot tube/flue length. Try to guess the (simple) answer: to give you a chance to guess, I'm putting the answer in another post below this one.

Continuing the Niagara/NKP Berkshire comparison. The way the Berkshire gets so much tube and flue heating area is, of course, by having more tubes and flues. In detail: the NKP engine had 77 tubes and 202 flues, the Niagara only 55 tubes and 177 flues. (Type E superheater elements-- both engines had Type E-- were a standard item, and were inside the flues. So, with an equivalent length of flue, superheating area ought to be proportional to the number of flues... which it seems to be. Doing the division, the NKP engine had 11.1 square feet of superheating surface per flue, and the Niagara 11.16.)

But, of course, this leads to the question of how they fitted all those tubes and flues inside the Berkshire's skinny boiler... Well, not really SKINNY, but with a 98" maximum diameter, the NKP engine's boiler had about 4% less cross sectional area than the Niagara's 100" boiler. Solution: use smaller pipes. The tubes were 2.25" diameter in both engines, but whereas the Niagara had 4" flues, the flues in the Berkshire boiler-- though accommodating the same sized superheater elements-- were only 3.5". (I just checked the arithmetic: the flue-tube surface areas of the two boilers ARE, as they ought to be, proportional the totals of the circumferences of their tubes and flues.)

So. What does this tell us about boiler design? The point of the exercise is to transfer heat from the furnace gasses to the boiler water, so you might think maximizing the heating surface would be a good idea. But there is another aspect to the problem. The exhaust gas has to get through the tubes and flues, and using smaller flues constricts the passage. To maintain the same firing rate (amount of coal burned per unit time), a boiler with small flues would have to have a more intense draft than one with large flues. Draft is created by exhaust steam directed up the "blast pipe" into the bottom of the smokestack: to get a more intense draft, more energy has to be in the exhaust steam... and energy used to create draft in the smokestack ISN'T being used to push the pistons backand forth in the cylinders. So there is a trade-off.

The designers of the Niagara-- some combination of Paul Kiefer's team at the New York Central and Alco's engineering staff, most likely influenced by the theoretical writings of the great French locomotive designer André Chapelon-- evidently felt that the advantages of freeing up the flow of gas through the boiler by using larger flues outweighed those of maximizing heating surface by using smaller ones. Whoever wrote the article for "Railway Mechanical Engineer" evidently thought this was an important issue: one of the figures given in the table of "General Dimensions and Proportions of the Boiler" is "Net gas area through tubes and flues." I can't do the relevant calculations-- the "Net" cross sectional area of a flue would be the total area of the flue minus the cross sectional area of the superheater element, and I don't know what that is... in addition to not knowing whether the diameters given for tubes and flues are external or internal-- but I'd bet the Niagara's boiler has a significantly greater "Net gas area" than the Berkshire's. And that this is part of why the NKP Berkshire was merely GREAT and the Niagara was SUPERLATIVE!

Back to the A-2. No feed water heater: sniff. But the basic boiler design-- in such respects as "Net gas area through tubes and flues"-- was ultra-modern. So, maybe ONE motivation for the A-2 was the desire to experiment: how good a locomotive can we build by using optimized boiler proportions without adding high-cost extras like feedwater heaters?

Edson/May has a small A-2 diagram with the tube/flue count.

The A-2 is a beefy-looking engine, to be sure. Regarding whether other than P&LE engines in the NYC System had overfire jets, what is the difference between overfire jets and "smoke consumers"? The latter are referred to in the 1944 New York State training manual for firemen, based on NYC practice, http://www.railarchive.net/firing. Also, what is that complicated-looking device on the left side of the A-2, just under the running board in the space between the cylinder assembly and the valve gear frame? Also what are those two fixtures sitting on top of the valve chest, connected by a pipe? (Photo is here, http://www.railarchive.net/nyccollection/ple9405.htm).

If it wasn't mentioned above, the New York Central System Historical Society is offering Mechanical Department drawings of the A-2 on CD here: http://nycshs.blogspot.com/search/label/books.