THE SMOKE-STACK.
The ordinary purpose of the smoke-stack is to convey the smoke and exhausted gases to the atmosphere. If it is intended to perform its functions in a straightforward manner, it is made about the same diameter as the cylinders, and its highest altitude rises from 14 to 15 feet above the rail. The stack is a simple-enough article to look at, yet a vast amount of inventive genius has been expended upon attempts to expand its natural functions. Attempts have been made to utilize it as an apparatus for consuming smoke, and hundreds of patents hang upon it as a spark-arrester. Patentees, in pushing their hobby, seem occasionally to forget that a locomotive requires some draught, as a means of generating steam; and stacks are frequently so hampered with patent spark-arresters that the means of making steam are seriously curtailed. Were it not for the danger of raising fires by spark-throwing, it would be more economical to use engines with clear smoke-stacks; and the extended front end, with open stack, is a good move in this direction.
OBSTRUCTIONS TO DRAUGHT.
Every obstruction to free draught entails the use of strong artificial means to overcome it. The usual resort is contracted nozzles, which induce a sharp blast, and use up more fuel than would be required with an open passage to the atmosphere. Among the obstacles to free steaming, that come under the category of obstructed draught, may be placed a wide cone fastened low, and netting with fine meshes. When the draught passage is interrupted to a pernicious extent by spark-arresting appliances, their effects can be perceived on the fire when steam is shut off; for the flame and smoke prefer the fire-box door to the stack as a means of exit. Sometimes steam-making is hindered by the netting getting gummed up with spent lubricants and dirt from the cylinders. Cases occur where this gum has to be burned off before free draught can be obtained. Waste soaked with coal-oil will generally burn off the objectionable coating.
CHOKING THE NETTING WITH OIL.
Gumming of the netting is usually caused by carelessness in oiling the valves. Some runners will shut off for a minute while the fireman oils the valves, and the lubricant scarcely gets time to reach the steam-chest when the throttle is opened wide again; and instead of soaking over valves and cylinders, and into the remotest part of piston-packing, the oil goes through the stack with the first puff of steam. It is best, in oiling the valves, to leave the cup-plugs open long enough for the oil to be sucked out of the pipes. Then, when steam is applied, it should be done by slightly opening the throttle, so that it will work the oil into the piston-packing; and, after a few turns run this way, there will be no loose oil left to defile the netting.
SILICIOUS DEPOSIT ON FLUE-SHEET.
Certain kinds of coal deposit a hard, silicious substance upon the back flue-sheet, which gradually accumulates till the draught is seriously impeded. This, of course, prevents the full benefit of the hot gases being obtained; and consequently the steam goes down. Flues stopped up with cinders produce a similar effect. The flues getting choked up with cinders is not always an indication that the petticoat-pipe is performing its duty improperly. Stopping up of flues is often caused by wild, unskillful firing. A shovelful of coal pitched high, deposits part of its load direct in the flues; and some pieces that are a close fit do not go through. They stick half way; and small cinders soon follow, that quickly close up the entire passage.