Note the two steam cylinders. The Cog engines don't have a "Johnson bar"(reverser) to control forward and reverse direction. Rather, this is done by two separate sets of cylinder's one for "forward steam" and one for "reverse steam" Exhaust steam leaving the cylinder's is vented out through a pipe and valve called a "sidestack". This controls the amount of "back pressure" on the exhaust side of the piston. In turn this aides the engineer to control the steam expansion rate and thus run the engine efficiently. Also note the two valves in the middle of the boiler, these are stop/check valves. This is where water is added to the boiler via the steam injectors and lines.

Photographed by Rich Currie, November 3, 2006.
Added to the photo archive by Rich Currie, November 12, 2006.
Railroad: Mt. Washington Cog Railway.

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