All About Engines

 Raising Steam is so great that nearly 25 is ejected through the flues condition when the boiler is of evaporation. In a stationary engine of would think of passing exhaust steam into the chimney, and on a ship fresh water for the boilers is too valuable to be used for creating a draught. Moreover, in a tall chimney the steam would con- dense, and the shower of falling drops of water would themselves tend to set up motion in the opposite direction to that required. The simplest device for securing forced draught is to fix a door on the ash- pit and to deliver air into it from a fan. In that case the doors have to be a good fit, and an arrange- ment made whereby the fire-door cannot be opened without first closing the air valve. Otherwise the fuel would be blown out through the fire immediately it was opened. On ships a different method is employed. The stokehold is enclosed, and air is forced into it by means of a fan or fans. The imprisoned air, in its 89 per cent, of the fuel in a partially burnt forced to high rates any size no engineer door means of a fan or fans. efforts to escape, rushes through the firebars and causes the fuel to blaze briskly. The stokers are, therefore, working under increased pressure, though this is not very large. For land installations the closed stokehold is not practicable, and there are two other alternative methods in common use. One is to place a fan in the flue near the lower end of the chimney, so that the gases are propelled forwards. It is, however, The stokers are,