Ash Pans. Ash pans are suspended beneath the fire-box for the purpose of catching and carrying the ashes and coal that may drop between the grate bars. They are made of sheet steel. Fig. 49 illustrates a longitudinal section of an ash pan commonly used in fire-boxes placed between the axles of the engine. It is provided at each end with a damper a hinged at the top and which may be opened and set in any desired position in order to regulate the flow of air to the fire. It is quite important that the dampers should be in good condition in order that the admission of air to the file may be regulated. The total unobstructed air openings in the ash pan need not exceed the total tube area but should not be less than 75 per cent. For many years the type shown in Fig. 49 was almost universally used. More recently, however, a damper capable of better adjustment and more easily kept in condition has been developed. Such a damper is illustrated in Fig. 50. In this type the dampers are placed upon the front faces of the ash pan and are raised and lowered by the contraction of levers and bell cranks. For example, the lifting of the bar a turns the bell crank d which pulls the connection c c which operates the forward bell crank and opens the front damper. In a similar manner, the rear damper i may be operated. If these dampers were made of cast iron and work in guides, it is possible to have the construction such that when closed they will be practically air tight.
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