tapered boilers on AMERICAN steamers

[alinfred]

what was the reason for having tapered boilers on AMERICAN steamers,I have many thoughts on this subject,one being forward vision,BIG BOY cancels that theory,any thoughts

[Overmod]

Nobody seems to be answering this, so let me throw out some comments.

1) There are good engineering reasons for the taper. IIRC, Alco history from the Cole years contains some specific discussions of it.

2) When Stanier et al. did the original Princess boilers, they (supposedly) took the design from the PRR K4, specifically including the taper, and scaled things down to fit the more restricted loading gauge. The reasoning behind this is probably documented in British sources.

3) Note that some later American practice (e.g. the NYC NIagara) involved return to untapered profiles, at least on the top of the boiler.

Part of the reason for the taper involves the desire to preserve an external steam dome while maximizing the diameter of the boiler at the forward end of the crown sheet and combustion chamber (and when using a large grate area that has to be 'faired in' to the convective sections of the boiler). Likewise, the 'reverse taper' often seen in the firebox may show, in part, the desire to have a 'turret' in front of a cab whose roof and sides clear the loading gauge, while preserving max dimensions of boiler in the critical areas.

Sizing the boiler for 'most efficient' use of steel, accommodating the cross-sectional profile to optimize gas flow, recognizing that the tube section of the boiler requires a smaller cross-section than parts of the firebox, and weight distribution of a water-filled boiler over the locomotive's wheels and suspension are also reasons to employ some taper in design.

I'm unfamiliar with Russian (and IIRC some Chinese) design practice regarding type of taper used when the dry pipe is physically located outside the boiler. Some research here might provide useful further insight.

Let's hear from some of the knowledgeable steam people!