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Re the addition of the portable engine image, are we correct in including those boilers were the firebox is round-topped (and so has the staying problem), but where it is raised above the barrel line (see the VoR image), thus removing the round-topped boiler's main claim to simplicity? Is there a distinct term for such designs? I can't quite see which it is for the portable engine, but many such engines did have raised firebox wrappers. Andy Dingley (talk) 15:23, 10 January 2011 (UTC)[reply]
Hmmm...well, you're the expert! Portable engine references were added on the basis of the information provided in the article. (This image was chosen as the clearest example of the firebox end -- we're rather short of good pictures of portable engines.) As they are the earliest and simplest examples of movable steam engines, it seemed a reasonably safe connection to make. -- EdJogg (talk) 17:23, 10 January 2011 (UTC)[reply]
I've not found anything really solid as yet. It appears that the "raised firebox" (either under that name, or else the full-blown "haystack") was the original form and the fully-flush wrapper appeared around 1850, due to Crampton. What I don't understand is how the "transitional" form persisted, where firebox outer was only slightly larger and was connected by a rolled angle-iron half-ring. This gave no advantage for the avoidance of priming, yet must surely have been more complicated to make?
Some interesting stuff has turned up on Belpaire though. It seems that the metallurgy of iron vs. steel was quite influential here. The Belpaire design can't be made economically without heavy hydraulic press tooling (which thanks to Bramah was now available), yet this in turn depends on the use of steel plates rather than wrought iron. The ductility of iron varies significantly with bending radius: although it can be rolled, only steel could be pressed in the cornered dies needed for Belpaire. Andy Dingley (talk) 02:12, 11 January 2011 (UTC)[reply]
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