All About Engines

Raising Steam 85 world—a job requiring merely moderate watchfulness and physical strength. And yet if the production of steam is to be maintained and coal is to be econo- mised, there are few tasks which are more difficult. A careless stoker will allow the fire to burn too low and will then pile on coal to such an extent that the production of steam almost ceases for a time. And the excess of coal will result in a vast volume of black smoke consisting largely of combustible matter which ought to have been burnt before it left the furnace. Moreover, it is impossible for coal to be shovelled in without opening the door, and every time the door is opened there is a rush of cold air through the flues or tubes, reducing the temperature of all those parts which should be kept hot. A really careful man will put on only small quan- tities of fuel at a time. He will place it near the door so that the volatile matters which come off are consumed as they pass over the hotter portion. Or he will scatter it lightly over the whole fire to secure the same effect. But no man can be so regular as a machine, and as fuel can be fed in with a machine without opening the door, all large well-managed boilers are fitted with mechanical stokers. In one form a hopper, like a funnel, is fixed in front of the boiler in such a position that its lower end is level with the upper edge of the fire door opening. Below this hopper, and instead of a fire door, is a chamber fitted with a ram or piston which moves backwards and forwards in a horizontal direction. When the ram moves back coal falls from the hopper,