THE EXTENDED SMOKE-BOX.
By this arrangement, the spark-arresting device is transferred from the smoke-stack to the smoke-box, and the exhaust steam escapes direct to the atmosphere, without meeting obstruction from a cone or netting. The netting is generally an oblong screen, extending from above the upper row of flues to the top of the extended smoke-box, some distance ahead of the stack. This presents a wide area of netting for the fire-gases to pass through. The draught through the flues is regulated by an apron or diaphragm-plate, extending downwards at an acute angle from the upper part of the flue-sheet. With the long exhaust-pipe used with the extended smoke-box, the tendency of the exhaust is to draw the fire-gases through the upper row of flues. The diaphragm-plate performs the same duties here, of regulating the draught through the flues equally, as the petticoat-pipe does with the diamond-stack. It is of great consequence, for the successful working of the engine, that the draught should be properly regulated: otherwise there will be trouble for want of steam.
When an engine having an extended smoke-box does not steam properly, experiments should be made with the diaphragm fastened at different angles, till the point is reached where equal draught through the flues is obtained. Closing the nozzles, as a means of improving the steaming of such an engine, is certain to make matters worse.