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(b) If the total pressure drop from the ash-pit to uptake remains constant, the pressure drop through any portion of the gas path will vary in the same direction as does the resistance to the flow of the gases, although the magnitudes of the variations may not necessarily be in simple proportion. Suppose the total pressure drop is 0.50 inch of water and the drop through the fuel bed is 0.25 inch, if the total drop be kept constant, but the resistance through the fuel bed be increased to about 0.32 inch of water; or if, for the same total drop, the resistance of the fuel bed be increased by quadrupling the thickness, the drop through the bed will increase to about 0.40.
(c) When the resistance through any portion of the gas path remains constant the weight of gas passing through this portion varies with some power of the pressure drop through this portion. Thus, since the resistance of that portion of the gas path from over the fire bed to the uptake is generally nearly constant, the weight of gas passing through the furnace and boiler varies as some power of the pressure drop between these points. It has been determined by experiment that the weight of gases passing through the boiler is, approximately, directly proportional to the square root of the pressure drop through the boiler or through any other portion of the gas path having constant resistance.
In order to obtain economy, the “ draft" must be a subject of daily discussion and study. Every officer and man on board ship must be made to understand what “ draft” is and how to use it. Er scientia tridens.
The TIME-FIRING DEVICE The use of the time-firing device was made standard for all steaming watches. Individual ideas of operation were not allowed and the rules laid down had to be followed at all times. The time-firing device and its purpose was explained to the officers and men. It was found that in order to be of real value cooperation from the bridge was necessary. Accordingly, instructions for its use were given to the deck officers and it was explained to them how they could assist. Any signals of change of speed were sent at once to the engine-room, including use of speed cones by ships ahead, and it was endeavored to anticipate speed changes if possible. The officers of the deck also kept the engineroom informed of matters of interest and the men on watch were
evidently does not know how to fire properly. He adds to his work, for he cannot be, and you may be sure he is not, hitting the back of the grates, so he must use his hoe (with enormous loss of heat and an extreme supply of cool air through the open door) to shove the coal back. Holes are also sure to occur at the back of the grate. Also coal scattered around not only makes the fire-room look dirty, but it makes it hard to walk around.
FIRING INTERVAL AND AMOUNT FIRED Each TIME The coal used in our navy is soft (bituminous) coal and to be burned properly must be fired at short intervals in small amounts. The depth or thickness of the fire depends entirely upon the amount of air supplied to it: fires will be thin at natural draft and will be the thickest when maximum full power forced draft is used. By firing in small amounts the coal supply is more nearly proportional to the air supply in the average, and will reduce the formation of crust on the tops of the fires and the chances of holes forming in the fire bed. Better combustion is also obtained, and it may be taken that 15 pounds of air are needed for each pound of coal fired. The more uniform the rate of air supply below and above the grates and the more uniform the coaling of the fires, the cleaner the fires will remain and the necessary amount of coal will become less.
When a shovel full of coal is spread over a hot, radiant fuel bed, the coal is heated rapidly and about one-third of the combustible matter is distilled off in the form of gases and tar vapors; and this distillation will be all over, completed in about one to four minutes (according to firing interval and amount fired). This distilled combustible matter requires additional air for its complete burning and this air enters through the fire door. The heavier the chargings become, the larger will be the amount of combustible distilled off, and accordingly the greater must be the air supply through the door to the top of the fire. Our boilers were built by the same firm, have the same size furnace doors, same size grates, same size ventilators, same size fire-rooms, same openings in furnace doors, same size ash-pits and ash-pit doors and the same uptakes and dampers (excepting, of course, boilers Nos. 5 and 6, which are slightly smaller). Every one knows our boilers are all the same size (except Nos. 5 and 6) and yet if all 14 boilers are steaming would an inspection show all fires exactly alike? No! Each boiler does one-fourteenth part of the steaming (in port on auxiliary watch with two boilers, each does one-half), but is each boiler getting one-fourteenth of the air supply? Is each boiler getting one-fourteenth of the coal burned? Is each boiler really doing one-fourteenth of the steaming? No! I have yet to see a watch where this is entirely so. It depends entirely on the chief water tenders, who must see that all furnaces of all boilers under them are fired alike, sliced alike, handled alike, and all ash-pans cleaned, and they must demand and exact a complete uniformity of their entire watch. Not only is this "equalness" of great importance, but it is criminal to do otherwise, for such an extremely large amount of extra work is made necessary, and if fires are not uniform what work is done will be of low performance.
To burn the volatile combustible driven off, about 15 times its weight in air is required. This air is supplied through the open furnace door when coaling and through the openings around the door when it is shut. If you use a lot of coal each time the door should be open longer than when you fire only a little at a time. You men do not change the length of time you keep your door open, you cannot and must not do so. Your orders are: To keep the furnace doors shut as much as possible; to use three light shovelfuls of coal; to follow the time firing interval; and to place the coal only where it is needed. All men are not doing this and any man who cannot carry out these simple rules for firing should be disrated and taken off the fires.
Regulating the supply of air through furnace doors to the top of the fire bed is not possible. Some doors are warped more than others, some doors shut tighter, some firemen keep theirs open a longer time than others, and so the air to the top of the various fires is different; and yet if everything, draft included, is made equal and uniform throughout the fire-rooms, the amount of the distilled combustible given off from the surface of the fuel beds will be the same, and the above mechanical difficulties are taken care of. They are further reduced and the boilers do still better work if coal is fired in smaller amounts and in short intervals. It is far more efficient and better to use four one-half shovelfuls fired every two minutes than three heaping shovelfuls fired every three minutes; for not only do fires grow equally and uniformly, but it is also much easier to put the coal where it is needed. By light, frequent firing, the distillation of volatile combustible is made nearly uniform and it is at all times nearly proportional to the air supply. Fires will be cleaner, better and easier to handle.
In closing this first talk it is desirous to summarize the points brought out. This may well be done by comparing what a GOOD fire is with what a bad fire is (see page 598). A good fire is one that is :
bright the fire is too thin, or there is a hole of large
size in the fire, or there are many holes. e. Top of fire bed light (white flames) all over. Such a fire
needs coal when its turn comes. f. A good fire is one that has an even burst of flame (white)
from its entire surface; the bottom of the fire bed has a layer of fine ash that will fall into the grates when the slice bar is swept through it and this will also indicate
that the fireman is putting his coal where it is needed. g. Clean boiler front and floor-plates.
THE SECOND TALK The word “draft" has been much abused by scientists and experimenters, but by the practical, operating engineer it simply names a condition that exists in his heat-producing system of boilers, fire-rooms, uptakes, smoke-pipes, the outside air, ventilators and blowers (either exhausting fans in the uptakes or pressure fans supplying air under the grates). This "condition produces the flow of air through the grates. It may be such as to cause a lot of air to flow, as occurs when the fire-rooms are closed and the large forced draft blowers are running, or it may be cut down by closing the dampers or stopped entirely by sealing up the boiler front.
There is not a fireman but knows that when the blowers are running it is necessary to carry heavier fires than when they are stopped. As soon as the forced draft blowers are stopped, the ventilators (openings to the outside air) must be opened. Then, instead of having the blowers creating the pressure, there is a
THE UNITED STATES COAST GUARD: ITS
FOREWORD The following paper was prepared several months prior to the outbreak of the present war, but it has been impracticable to print it until now.
The fact has become apparent that in the past the navy and the coast guard have not gotten sufficiently close together, but it is thought that from the beneficial results attending present association, each service will have appreciated the worth of the officers of the other, to the mutual advantage of the two services and the public interests.
Since mobilization, the enlisted personnel of the coast guard has increased until it now numbers about 6000 men—2000 more than on a peace basis—and many changes have transpired as to the disposition of the entire personnel, which is now scattered among coast guard ships, naval vessels, at air stations, in Washington, and in the several naval districts, and the need for experienced officers has been urgent.
It is suggested that now is the psychological moment to make a mental survey of conditions, to take a look at them from a fair, unbiased viewpoint, and thus to realize the errors of the past, brought about as they have been by misunderstandings and a lack of knowledge of facts.
The AUTHOR This paper has been written with the single idea of presenting to the officers of the navy and coast guard tentative suggestions for increasing the military efficiency of the latter service, which, if adopted, would be in the best interests of the navy and the