hank Wrote:
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> You'd need to ask an engineer (the kind that
> designs them, not the kind tha runs them) to get a
> definitive answer to that.
> To get you started though, the boiler for the D&RG
> class 45.5 engines (#'s 158-165) had the following
> stats:
> FB: length inside = 57", width inside = 25", Ht,
> front = 45", back = 44.5"
> Flues: # of 132, OD = 2", length = 10'-9".
> Grate surface- sq ft = 9.89
> Heating surface(sq ft): Flues = 729.8, FB = 60.0,
> total = 789.8
> (Information from Folio #4, sheet #1. Reprinted in
> CRA #24 - pg 254) BP not listed but I'd guess
> 145#.
> Note: This data would be ca. 1904 or so. Just
> looking at the stats not to very different from
> the Class 47 engines. I wonder, if there had been
> a percieved need for more little 4-6-0's in 1912,
> would the 45.5s gotten the same new boilers as the
> Class 47s and wound up as T-12s? Sorta the
> opposite of the Class 70 engines winding up in two
> (C-17 & C-19) classes?
Your numbers are interesting as they appear to reference re-boilered class 45.5 engines rather than their as-built configuration. I don't know how many of them received new boilers, but at least some of them did--early too--as one of them was the engine used in the D&RG's pioneering of the extended wagon top boiler design during the mid-late 1880's. This re-boiler project has always seemed a little odd to me. I haven't heard of members of the class being ruined in wrecks during their first few years, but a railroad isn't going to rebuild a practically-new locomotive just for the fun of it. I surmise the class, while steadier than the class 45 moguls, probably proved a little short of breath when run at express speeds.
As-built class 45½ had 42 inch diameter straight iron boilers with 95 two-inch diameter tubes 10 feet 8 inches long. This is confirmed by a quick check of the builder's specifications. The overall heating surface was not impressive and they must have steamed more like freight locomotives than express passenger engines. The firebox you list appears basically similar size to its as-built configuration which isn't a shock as it'd have been constrained by space above the frames and between the axles. I'd be shocked if the original boiler pressure was anything higher than 130 pounds. Even the class 70 locomotives ordered in late 1886 with steel boilers (later C-17) were originally specified with 130 pounds boiler pressure....soon to be raised. The D&RG reported that it liked engines 158-165, at least relative to the high-drivered Moguls, yet it ordered no more of the type and its next narrow gauge 4-6-0's had the same cylinder size but with a larger boiler and firebox. That's hardly a resounding endorsement.
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The answer to how much boiler you need for a given locomotive isn't a fixed answer, anyhow. Baldwin, for example, produced narrow gauge 12x16 4-4-0's in various sizes with heating surface totals ranging from about 380 to upwards of 560 square feet and all of them worked. More boiler will usually mean you have a faster locomotive since you have more steam generation and hence higher horsepower. Superheating also affects this since you can get more work from less steam. In the other direction, a smaller boiler means you have a lighter locomotive that can run on lighter rails, and at any rate high speeds aren't usually desired on lightly-laid lines anyhow.
