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bottom of the boiler should be swept clean of ashes and examined for any defects, such as fire cracks about the rivets most exposed to the heat. These cracks may often exist some time before being discovered unless a close inspection is made. They are small cracks radiating from the rivet holes outward past the rivet heads one-half to three-quarters of an inch, and are always liable to extend farther until they become a source of danger unless arrested in time. They may be closed up sometimes with the caulking tool, but if one should be found several inches in length, a hole should be drilled at the outer end of the crack and a rivet put in. This will generally stop it.
Fire cracks occur in the girth seams only, and especially the seam nearest the fire.
It is essential that the bridge walls of horizontal boilers be kept in good repair, in order that as much fire brick surface as possible may be exposed to the heat. This will greatly aid combustion and prevent smoke.
Firing Up. After the boiler washer has completed his task the next thing in order is firing up, and in doing this if care and good judgment are not exercised there is danger of doing much damage to the boiler, especially if it has been filled with cold water. A very light fire should be started at first and kept that way until the water gets to the boiling point at least, after which the fire may be gradually increased until the steam gauge shợws a few pounds pressure, when it will be safe to urge the fire still more. The bad effects resulting from the unequal expansion or contraction of the sheets and undue stress upon the rivets, all caused by rapid changes of the temperature of the boiler from hot to cold or vice versa, cannot be
guarded against too carefully, and they are liable to be brought about in two ways: first, by haste in cooling down a hot boiler that is to be washed out, and secondly, by starting a heavy fire under a cold boiler. That part of the boiler most exposed to the heat will become hot while other parts farthest removed from the fire may still be cold. Very often there is a difference of 150° or 200° in the teniperature of different parts of the boiler for a time during the firing up process, and the same dangerous conditions may be caused also by blowing all the water out of a boiler while under a pressure of 15 or 20 lbs., as is the custom of some persons when preparing a boiler for washing out. Either custom cannot be too strongly condemned.
Sometimes a boiler is needed in a hurry after having been washed out, and in such an emergency it should be filled with warm water; in fact, it is better to always fill a boiler with warm water if it is possible to do so after washing out.
Connecting with the Main Header. When the gauge shows a pressure that is within 10 or 15 lbs. of being the same as that carried on the other boilers it should be watched closely, and when the pressure becomes the same as that in the main the connecting valve should be opened slightly, just sufficient to allow a light flow of steam through it, which can be easily detected by placing the ear near the valve chamber. This steam may be passing from the boiler to the header or vice versa, but whichever way it is going the valve should not be opened any farther until the pressure in the main pipe and in the boiler is equalized, when it will be found that the valve may be opened easily. While connecting the boiler the dampers should be closed.
Care should always be exercised in connecting a recently fired up boiler, and the engineer should be certain that the steam gauge and pop valve are in good working order. Otherwise there is liability of a serious accident occurring, either in breakage of the steam pipe, or what is still worse, a bciler explosion
Principles involved in the action of automatic stokers-Advan.
tages and disadvantages attending their use-Classification and general description of stokers-Coal-handling machinery -Under-feed stokers-Mansfield chain grate stoker—Playford stoker-Vicars mechanical stoker-The Wilkinson stokerMurphy stoker-Roney stoker-The American under-feed stoker—The Jones under-feed stoker-Outside furnaces-Con. ditions required in a boiler furnace to ensure good combus. tion-Hindrances to good combustion-Description of Burke outside furnace. The principles governing the operation of mechanical or automatic stokers are in the main correct, viz., that the supply of coal and air is continuous and that provision is made for the regulation of the supply of fuel according to the demand upon the boiler for steam; also that the intermittent opening and closing of the furnace doors, as in hand firing, thereby admitting a large volume of cold air directly into the furnace on top of the fire, is avoided.
Mechanical stokers have within the last twelve years been largely adopted in the United States, especially in sections where bituminous coal is the principal fuel. The disadvantages attending their use are:
First, that the cost of properly installing them is so great that their use is practically prohibited to the small manufacturer.
Second, that in case of a sudden demand upon the boilers for more steam the automatic stoker cannot respond as promptly as in hand firing, although
this objection could no doubt be met by skillful handling
Third, the extra cost for power to operate them, although this is probably offset by the diminished expense for labor required, as compared to hand firing.
There are many different types of mechanical stokers and automatic furnaces, but they may for convenience be grouped into four general classes. In class one the grate consists of an endless chain of short bars that travel in a horizostal, 'irection over sprocket wheels, operated either by a small an kiliary engine or by power derived from an overhead line u: shafting in front of the boilers.
In class two may be included stokers having grate bars somewhat after the ordinary type as to length and size, but having a continuous motion up and down or forward and back. This motion, though slight, serves to keep the fuel stirred and loosened, thus preventing the firing from becoming sluggish. The grate bars in this class of stokers are either horizontal or inclined at a slight angle, and their constant motion tends to gradually advance the coal from the front to the back end of the furnace.
Class three includes stokers having the grate, bars steeply inclined.
Slow motion is imparted to the grates, the coal being fed onto the upper end and forced forward as fast as required.
Class four includes an entirely different type of stoker, in that the fresh coal is supplied underneath the grates, and is pushed up through an opening left for the purpose midway of the furnace. The gases; on being distilled, immediately come in contact with the hot bed of coke on top and the result is good com bustion. In this type of stoker steam is the active ageut used for forcing the coal up into the furnace, eithe: