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.
STEAM-PIPES LEAKING.
The blowing of steam-pipe joints in the smoke-box is very disastrous to the steaming qualities of a locomotive. This has a double action against keeping up steam. All that escapes by leaking is so much wasted, and its presence in the smoke-box interrupts the draught.
If the steam-pipe joints are leaking badly, they can be heard when the fire-door is open and the engine working steam. Some experienced engineers can detect the action of leaky steam-pipe joints on the fire; but the safest way to locate this trouble is by opening the smoke-box door, and giving the engine steam.
DEFECTS OF GRATES.
Grates that are fitted so close as to curtail the free admission of air below the fire prevent an engine from steaming freely. The effect of this will be most apparent when the fire begins to get dirty. This is not a common fault. I once knew of an engine’s steaming being very seriously impaired by two or three fingers in one section of grate being broken off. The engine steamed well with a light fire, till, in dumping the fire at the end of a journey, the men knocked some of the fingers off. Next trip, it seemed a different engine. Nothing but heavy firing would keep up an approach at working-pressure. I experimented with the petticoat-pipe without satisfaction, assured myself that no leaks existed among the pipes; the stack, with its connections, was faultless; and the engineer was puzzled. The defect was discovered by watching the effect of the blast upon the fire. Signs of air-drawing were often to be seen at the point where the broken fingers were. This was where the mischief lay. Too much cold air came through, unless the opening were bedded over by heavy fire.
A drop-grate that did not close properly had a similar effect upon another engine which came under the author’s notice; and a change, which shut the opening, effected a perfect remedy.
LIME, SCALE, AND MUD.
In calcareous regions, where the water-supply for locomotives is drawn from wells, the most common cause for bad-steaming engines is leaky heating-surfaces, or water-surfaces incrusted with lime deposits. When he sees water pouring from flues and stay-bolts, an engineer has no difficulty in divining the reason why his engine steams poorly; nor need he be far-seeing to perceive a remedy in the boiler-maker’s calking-tools skillfully applied. The case of incrustation is, however, more difficult to comprehend in all its bearings. When water containing lime-salts touches the hot flues or fire-box, evaporation takes place; and the solid substance previously in solution is left behind, and adheres to the heating-surfaces, gradually forming a refractory scale which is an indifferent conductor of heat. As this scale becomes thick, it stands up, like a non-conducting barrier, between the water and the hot sheets; and it takes a much greater expenditure of heat to evaporate the water inside, just as a kettle coated with scale is much harder to boil than a clean one. When a boiler gets badly fouled with scale and mud, these impurities exercise a pernicious effect upon the steaming qualities of a locomotive.