All About Engines

go All About Engines rather hard on the fan, and the hot gases have a serious effect on the bearings, which have to be cooled by water. The other plan is to place the fan outside the flue and to force air through a jet into the chimney. In this case the chimney in the neighbourhood of the jet must be of special form to render the jet effective. Twenty years ago artificial draught was only adopted in cases where the natural draught was bad; but to-day the demand for a high rate of combustion renders artificial means necessary wherever power is produced in large quantities. Feed-water Heating and Regulating Every pound of cold water delivered to the boiler must be heated to the boiling point before it is con- verted into steam, so that if some of the heat which fails to enter the water in the boiler can be utilised to warm the feed water, a great saving in fuel may be effected. Thus if the initial temperature of the water is 50° Fahr., or io° C., and it is raised to 120° Fahr, or 48.9° C., before entering the boiler, the saving in fuel is nearly 6 per cent. Assuming the same initial temperatures, the following table gives the saving when the water is heated to a greater extent: Temperature on entering boiler 140° Fahr., or 6o° C. 1600 Fahr., or 71.i° C. 1800 Fahr., or 82-2° C. Saving of fuel . 7.65 per cent. . 9.34 per cent. . 11.04 per cent.