December 13th - 3rd Coast Photography

The steam you see coming out from the cylinders is actually controlled by the engineer, via what are called the "cylinder cocks". These are ports in the cylinder that can be opened to allow steam and/or water to escape, and the reason you would want to provide them is simple. When starting, a locomotive's cylinders are relatively cool compared to the incoming steam, and water, liquid water, will condense out in the cylinders. These cylinder cocks allow the liquid water, along with some steam of course, to escape, preventing the cylinder heads from damage or being blown off, as liquid water does not compress!

Pere Marquette 1225
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