Superheating.

Superheating is of course a form, and a very important form, of fuel economy. You are all familiar with superheater engines and the principle of superheat, which not only increases the steaming capacity of the boiler, but at the same time permits the use of larger cylinders because the superheat prevents the cylinder condensation. The steam and coal economy obtained with superheater locomotives which is equivalent to a corresponding increase of the boiler capacity has made it possible in many cases to reduce the boiler pressure.

Professor Goss on “The Use of Superheated Steam in Locomotive Service”:—

“Neither steam nor coal consumption is materially affected by considerable changes in boiler pressure, a, fact which justifies the use of comparatively low pressures in connection with superheat.”

Before we got the use of superheat in boilers the pressures were being gradually put up, whereas they are now down to 180/200 for passenger engines and 160/180 for goods engines.

The economical results obtained with superheater locomotives show considerable savings in coal. In passenger engines it is not so much the coal saving which makes superheater engines so popular, but the increase in power obtained and the better way in which the superheater engine handles the train. The great feature of a superheater engine is that its efficiency increases with the demand for power. If an ordinary wet engine is forced, its efficiency decreases on account of the increased wetness of the steam furnished by the boiler. The super-heater, however, on the contrary, improves with increased demands, since the degree of superheat increases in proportion with the power the engine has to develop.

Professor Goss says:—

“In operation the degree of superheat increases with the increased rate of power, which tends to conserve the steam supply as the demand for power is increased.”

This flexibility is one of the main features that distinguishes the superheater from the wet and from the compound engines; and is, besides the coal and labour saved, the principal cause why superheater engines are such favourites with the men handling them.

(To be continued.)