Superheaters.

A cardinal improvement in steam engineering of late years has been in perfecting superheaters; this advance owes much to the mineral oils now available for lubrication at temperatures which may be as high as 675° Fahr. As steam expands to perform work it falls in temperature and much of it condenses as water, with marked loss of efficiency, with harm to its containers by severe hammering. A superheater avoids this trouble by so raising the initial temperature of the steam that condensation either ceases altogether or is much lessened. The apparatus is usually a nest of tubes placed in the fire-box close to the boiler; or, the tubes may be heated by a fire of their own, away from the boiler. The Schmidt superheater has long, parallel bent tubes, connecting two parallel headers. It may be directly applied to locomotive boilers without essential modification, and without checking the draft. On the Canadian Pacific Railway about two hundred simple locomotives have been provided with superheaters, lowering the coal consumption to 87, 85, 83 and as little as 76 per cent. in comparison with compound engines having no superheaters. At St. Louis in 1904 the Pennsylvania Railroad conducted elaborate tests of diverse locomotives. The most economical compound engine each hour used 18.6 pounds of ordinary saturated steam per indicated horse-power. Aided by a superheater this consumption was reduced to 16.6 pounds, a saving of 10.75 per cent. See page 241. In Germany portable steam engines of 150 to 220 horse-power, superheating their steam 150° to 170° Centigrade above the temperature of saturation have, in compound types, reduced their demand for steam to 12.47 pounds per horse-power hour and, in a triple-expansion model, to 9.97 pounds. In all cases the steam pipe takes the shortest possible path between its superheater and its cylinder.

A
Longitudinal section on a, b.

B
Cross-section on c, d.

C
Horizontal section on e, f.

Schmidt superheater.

[Enlarged illustration] (138 kB)