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Looks like a winding engine that hauls something up? The rope would go around the enormous wood-clad pulley.
Neat. It looks like these are [uniflow](http://en.wikipedia.org/wiki/Uniflow_steam_engine) engines. I wasn’t sure at first, but [this one](http://www.geograph.org.uk/photo/1591339), labeled as such, certainly appears to be a similar model from the same manufacturer.
As opposed to a [normal double-acting steam engine](http://www.rogercalvert.me.uk/images/ST5A.gif) where hot steam and cold exhaust are both allowed in and out through the same ports at the ends of the cylinder, a [uniflow engine ](http://en.wikipedia.org/wiki/Uniflow_steam_engine#mediaviewer/File:Uniflow_steam_engine.gif) allows in hot steam on the ends, and exhausts cold steam at the center.
The advantage of this setup is greater thermal efficiency. Because part of the heat from the steam being let in isn’t wasted reheating the pipe and cylinder head through which the cold steam just exited, there’s more power available to drive the piston.
The disadvantage is that, because the ends of the cylinder are always hotter than the center, they expand from more from the heat. This leads to the necessity of boring the cylinder slightly larger at the center than on the ends. In operation, heat and steam have to be managed with much greater precision because of these finicky tolerances. If temperature shifts too much or the steam is too ‘wet’, it can cause the engine to seize up and probably wreck your machinery.