Engineering Wonders of the World
Volume I

LOCOMOTIVE CONSTRUCTION.—VI. 256 DIAGRAMS TO SHOW THE ARRANGEMENT OF schmidt’s smoke tube superheater. SCHMIDT’S SMOKE-TUBE SUPERHEATER. Superheating signifies the heating of steam out of contact with water, and increasing its temperature without increasing its pressure in the same proportion. Superheating vaporizes any watery particles carried in the steam, and produces a true gas. The advantage of using very hot steam—up to 660° Fahrenheit—is that condensation and loss of volume caused by contact with the cylinder walls is lessened, and the steam can be used profitably with higher expansion ; so that superheating effects, in a different way, the kame purpose as “compounding” (passing the steam through two or more cylinders of increasing bore). The most widely used superheating apparatus is that illustrated above. On the way from the boiler to the cylinders the steam is led through tubes situated in special large smoke tubes or flues. The hot gases traversing the large tubes give up some of their heat to the water surrounding the tubes, and some to the steam inside the superheater tubes. The flow of heat through the large tubes is controlled by dampers hinged or pivoted below the steam collector in the smoke-box. The dampers are operated by a steam cylinder which, opens them when the regulator is opened, and vice versa. This prevents the superheating pipes from being unduly heated at any time. Tests have shown that a large increase—from 30 to 50 per cent.—of hauling power is effected by locomotives using highly superheated steam as compared with locomotives using saturated steam, the amount of coal consumed being the same in both cases ; also that water is greatly economized. Superheating has proved so successful that it is already a formidable rival, as well as ally, to compounding. DIAGRAM TO SHOW THE PRINCIPLE OF THE WALSCHAERT VALVE GEAR. As several references have been made on previous pages to this gear, which is now used widely on the Continent, in America, and elsewhere, a short description of its action will be interesting. The travel of the valve is the result of two movements combined—that of the cross-head, and that of an eccentric arranged usually at right angles to the crank. Reversal of the engine is effected by lifting or lowering the radius rod and the block attached thereto. If the last is in an oblique position, thø position erf the valve is altered. The gear is particularly suitable for locomotives with outside cylinders. On such the eccentric is usually replaced by a return crank attached to the end of the crank pin.