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8 MARINE REVIEW. Boilers, Circulation and Action--the " Scale Pan." [By fohn M. Sweeney of Harvey, Lil.) In the opinion of the writer there is nothing within the pro- vince of the "steam engineer" that is as'little understood and so worthy of investigation as the natural laws which govern the ptoperties of steam generators; the manner in which heat is taken up by the water, and the flow of energy through the plate. The discussion at the recent International Engineering Congress at the world's fair has demonstrated, however, that new interest is about to be taken in these questions. A boiler under conditions of natural draft, rendering satisfactory service with no leaks, is fitted with a forced draft appliance! Result-- leaky flues. Why does this happen? A flow of cold air into the furnace of a boiler results in leaky flues! What is the actual process through which the flues are caused to leak? It is almost a daily experience to see plates of boilers bagged, burned or in- jured by overheating of the plate. What is the phenomena oc- curring to bring about this effect ? It is not the intention in this paper to endeavor to investi- gate all these questions, but to describe, at present, a device now in use on many marine and stationary boilers, for the purpose of preventing the overheating of the plate, as covered in the last question, and to later take upa full discussion of the several questions in other papers. To the investigator in this field comes first to decide the temperature of the plate under proper working conditions, and right at the threshold of the investigation a halt must be called to discover this, the first essential. Recently there has appeared in leading mechanical journals some accounts of experiments undertaken to determine these temperatures; how they may vary with different thicknesses of plate, and dif- ferent temperatures of applied heat. Generally these experi- ments have been directed to a determination of results through the fusing or non-fusing of plugs of tin, lead, antimony or other substances placed in the plate, through which the heat was to be transmitted or through which the energy was to flow. It is well known to many engineers that a tea kettle or like vessel, in which water is made to boil or circulate, may be lifted from the fire and the hand applied to the botton of the vessel, which has been in contact with the fire, without injury to the hand or with- out any sense of heat being present in the bottom of the vessel. It is also well known that this low temperature will continne so long as the water continues to circulate. Later when the heat is transmitted from the water into the air, the temperature of the bottom rises to the temperature of the water, nearly, because the air is a slow absorbent and the resistance of the material in the bottom of the vessel is too great for the number of heat units offered. Applying this knowledge to boiler. practice, it must follow that in case of the occurrence of a bag, or burn, in a boiler plate, the temperature of the plate at that point has been raised. Asa matter of fact it will be found that scale or other matter has ac- cumulated inside of the boiler at the point where the bag occurs, and has prevented the water from contact with the plate on the inside. The water being absent at this particular point, nothing remains to absorb the energy which the plate stands ready to transmit; the plate becomes hot, and the pressure within the boiler forces the hot part out and produces the pocket or bag. Therefore, to prevent scale or other matter from accumulating on the plate in quantity to prevent wetting, is the most direct way to prevent bagging or burning. Since such bags occur over the hottest part of the fire, it is found only necessary to provide a relief where the furnace temperatures are the greatest, gener- ally over the grates. The device herewith shown is illustrated as placed in the bottom of an externally fired boiler, over the grates,and is known as a "scale pan," It can be placed equally well over the crown sheet of a fire box boiler, or over the top of a furnace, provision being made to clear the stays where necessary. 'The pan is made of say No. 14 B. G, sheet iron, about 5 feet long and gen- erally 12 to 14 inches wide, suitable for admission through the manhole opening into the boiler. In the case illustrated the pan is curved to a radius 2 inches less than the radius of the sheet of the boiler;this curvature being made the narrow way of the pan. The sides are flanged up for a width of about. 2 inches in order to slightly stiffen the pan, and to this flange are riveted two or three legs on each side, the legs being 2 inches long below the bottom of the pan and attached to the flange | of the pan with one rivet, so that they may be turned to lie with the flange on the pan, thus facilitating removal or return through the man hole opening. 'he legs are made of No. 14 sheet iron, and only about 114 inches wide, so that the amount of area in the end of the leg coming in contact with the sheet of the boiler is incon- siderable. ; ; The placing of this pan as described will prevent scale ac- cumulations on the sheet, but will cause accumulations within y 900000000000 \ | OOCOQ0CO000 | D(OOOOO0000000 | D0OOOO00O000000 0000000000000 00000000000 \, 2909900 the pan itself. Indeed if a punched washer or other foreign substance be placed onthe boiler sheet under the pan, before the boiler is closed and filled with water, it will invariably be found within the pan upon the opening of the boiler after use. One peculiar fact noted in the use of these pans, is that more scale in weight seems to be taken from the boiler with the pan than from the same boiler, performing, as nearly as can be the same evaporation, without the pan, which brings the query: What becomes of the scale and other matter received by the boiler? It is not the intention at this time to enter into an ex-. haustive discussion as to how or why the washer or scale goes into the pan; that will be taken up later. There is no patent on the "scale pan," and anyone troubled with bagged boilers will find it a boon indeed. fc The St. Clair Tunnel Company is considering the advisa- bility of adopting electric transit through the tunnel, and have~ secured estimates for such an equipment. 'The smoke from the engines is having a most serious effect upon the interior of the tunnel, and Chief Engineer Hobson is greatly concerned over the matter. The question of cost, however, is yet to be over- come before any definite action is taken. : The Deep Waterway Question. Editor MARINE Review: Referring to your editorial in the MARINE Review of August 24, I wish to state that the paper on "A Waterway from the Lakes to Tidewater,' although discussed by the delegates at the Water Commerce Congress, was written for and printed in the Railroad Gazette of July 7. In regard to the result that will probably be obtained on the comple- tion of the present contracts for deepening the channels of the lake waterways, the statement quoted in your editorial is simply a fact that may be easily veri- fied by any one who will take the trouble to investigate the matter. Details were not given for the reason that the subject was quite fully discussed ina paper printed in the Railroad Gazette of Feb. 3, and to which reference was made, The facts of the matter are that the present contracts are for channels 20 feet deep at mean lake level; that during seasons of low water the lake sur- face is from one to two feet below mean level, and that, owing to the shallow- ness of the water at the head of Lake Erie, strong westerly winds cause a lowering of the surface there of from one to six feet. It is therefore quite evident that during low water seasons the ayerage depth will be from 18 feet to 19 feet, and that during periods of westerly winds vessels of more than 16 feet draft will be very likely to have trouble in navigating the channel. This trouble is not noticeable in the present channel, for the reason that the depth at the head of Lake Erie, for mean level, is 3 feet greater than that in Lake St. Clair. When the channels across Lake St, Clair, however, are deepened to 20 feet, the fluctuation of the water surface at the head of Lake Erie will, without question, become a source of great annoyance to vessel interests. Detroit, Aug. 25, 1893. Gro. Y. WISNER. Subscribe for the official report of the Engineering Congress through the Marine Review. Price $10.