What do the following things mean? Saturated locomotive, slide valve locomotive? Also a 2-8-2 Mikado class MS would mean Mountain Superheated?
A saturated locomotive is one that ran on saturated steam. Steam at 212 degrees Fahrenheit. Those would be old (before the mid 1920's). In the mid 20's superheaters became popular, as they increased the power of a steam locomotive by leaps and bounds. Superheater tubes were installed in the flues of steam locomotives which allowed the saturated steam to be raised to much higher temperatures, about 700 degrees, resulting in tremendous increases in expansion and power delivered to the cylinders. Slide valves are also old on steam locomotives. If you look at a locomotive and it has rectangular, box-like structure above the cylinder/piston assembly, that contains a slide valve. More modern locomotives will have a cylindrical structure above the cylinders containing a circular cross section valve. Another difference between the two is outside vs. inside steam inlet to the cylinders, a whole other discussion. Locomotive classes were assigned by the railroads and have nothing to do with type of locomotive, except for that particular railroad. For instance the New York Central named their Hudsons, 4-6-4 wheel arrangement, class "J". There were J-1, J-2 and J-3 models built. The Norfolk and Western named their 4-8-4 locomotives class "J". About the only type that had any similarity among the railroads were Pacifics, 4-6-2's, which a whole lotta railroads called class "K". I don't know where "MS" came from, but ask more and we will try to get answers for you.
On steam locomotive classes, some railroads tried to use letters corresponding to the name of the wheel arrangement (SP was one). I.E., Pacifics were "P", Atlantics were "A", Consolidations were "C", 2-8-8-2's were Articulated Consolidations "AC", but when you come to "M", you've got a problem, there are Moguls, Mountains, and Mikados, so SP had "M" (2-6-0), "MK" (2-8-2), and "MT" (4-8-2). Numbers then followed the letters to 1.) indicate the design number (3 = third design), or, in the case of MP and DRGW, tractive effort (41 = 41,000 lbs. t.e.) Remember thuogh, these were individual to each railroad.
