An interesting article from the April, 1931 Frisco Employee's Magazine...as I don my dunce cap, perhaps others out there can help the newbie figure out the differences betwen saturated and superheated steam. More specifically, does the change become visible for modeler in the form of added appliances? Same goes for the "Type A" superheaters.--cla FRISCO MODERNIZES FOUR OLD TYPE ENGINES In 1904, the Frisco purchased five engines, Nos. 1010-1014 from the Baldwin Locomotive works. They were monsters of the time, new and shiny, and they were put in Frisco service and hauled many a ton of freight and many a passenger over Frisco Lines. One of them appears above [Picture of modernized No. 1014 accompanies the article-cla] In 1930, after twenty-six years of service, four of these engines were rebuilt at the Springfield West Shops. They were modernized in every way to make them economical engines, changing them from saturated steam to superheated steam. The total weight of engine and tender was originally 330,500 pounds and after being rebuilt it was 375,300. Tractice effort was also increased from 25,600 pounds to 28,250 pounds when rebuilt. The original weight of tender was 139,500. This was increased to 165,200 pounds. The boiler pressure remains at 200 pounds, but the cylinders were changed from slide valves to piston valves, and their diameter increased from twenty inches to twenty-one. The valve gear was changed from Stephenson to Walscheart, and the engines were equipped with "Type A" superheaters. The trailing truck, which was fabricated, was redesigned and made of cast steel, and the tank frame, which was also fabricated, was removed and a Commonwealth cast steel frame applied. Rolled steel trailer wheels, radial buffer, Commonwealth tender trucks, back pressure gauge and volatone air whistles were all applied. These engines are now operating on various divisions, but the 1014 is in service on the Texas Lines.
Thermodynamics, ah yes, ..... saturated steam is steam at equilibrium. In other words, at a given temperature and pressure, a certain amount of water will exist in a given volume as steam vapor, no more, no less, no liquid. As saturated steam does its work, the energy released is only latent heat - heat of vaporization/condensation, such that after a unit of saturated steam does its work and releases all of its latent energy, it is liquid condensate at the same temperature. Superheated steam is saturated steam that is heated in its vapor state to a higher temperature and pressure. As it does its work, the first energy to come out is reflected in a decrease in temperature and pressure, while still in the vapor state, until it reaches its saturated condition. Then latent heat starts to be released as above. Don't know about different appliances that would be visible on a steam locomotive. Didn't cover that in my thermo classes! Ken
Superheated engines require spool valves, which are more easily lubricated with fewer steam molecules, and will expand/contract more geometrically than will the square D-valves. Soaks may have D-valves or spool valves. Engines with front-end throttles are most likely superheated. Otherwise, it might be difficult to discern externally if an engine is superheated or not. The superheater elements are in the smoke box and flues.
Very good explanation, gentlemen. I would guess that I either dozed during those classes or, more likely, by taking a broadcasting degree, I slid through with the bare minimum in hard sciences. It helps to make a lot more sense of the old articles I've read. Thanks!
