The airway may be provided with a flap, to assist in damping down the
fire if too much steam is being raised. In the front end make an inspection
opening to facilitate cleaning the tubes and removing cinders, etc.
The side plates, m m, are bent as shown in Fig. 86, and bolted to a
semicircular top plate, n, bent to a radius of 6 inches. A slot, 1-1/2
inches wide and 11-1/2 inches long, must be cut in the top, n, to allow it
to be passed over drum D; and there must also be a 3 or 3-1/2 inch hole for
the chimney. A plate, p, covers in D. A little plate, o, is slipped over
the slot in n, and asbestos is packed in all round D. The interior of the
end, side, and the top plates should be lined with sheet asbestos held on
by large tin washers and screw bolts. To protect the asbestos, movable iron
sheets may be interposed on the furnace side. These are replaced easily if
burnt away. The pieces m m are bent out at the bottom, and screwed down to
a base-plate extending the whole length of the boiler.
The fire-bars fill the rectangle formed by the tubes B, El, and E2. A plate
extends from the top of E2 to the front plate of the casing, to prevent the
furnace draught being "short circuited.
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