On the Importance of Cleaning Steam-Boilers when Cold. (Bulletin de la Société Industrielle de Mulhouse, April-May, 1898, p. 66.) It is a bad system to empty boilers under steam pressure, when they have to be cleaned, to remove the deposit adhering to the boiler plates. This is the usual method with stokers, but there are two great inconveniences connected with it. The internal surfaces of the boiler plates are exposed to radiation from the hot surrounding brickwork, and the deposit during the process of emptying adheres to them and cannot be removed except by hammering. In the second place the riveted joints, affected by the radiation, and no longer covered with water, soon have a tendency to leak. Boilers should never be emptied until the steam pressure has fallen to about 1 atmosphere, or even less, and should be allowed if possible to become quite cold. The process of cleaning them thus, by means of a hose and water-jets, after carefully drawing off the water, is due to Mr. Savreuse of Amiens. Since 1886 it has been used for many boilers in France, and they have always been found very clean inside afterwards, the deposit comes away easily, and there is no necessity for chipping. To cool a boiler completely, when surrounded by brickwork, takes about 8 days altogether. After 3 days the flues can be cleared of the cinders and soot, and this helps to cool the water. A small steel scraper will be found useful to remove the harder deposit. B. D. Accidents to Steam-Boilers. (Annales des Ponts et Chaussées, 1898, p. 265.) A tabulated résumé, taken from the official reports, of the whole of the accidents occurring to steam boilers in France during the year 1896. The information given comprises the date and situation of the accident, details of each boiler, the circumstances attending the accident, and the consequences and presumed cause of each accident. In eighteen cases defective design and workmanship was the cause of the accident, the principal defects being: (1) parts made inaccessible to complete inspection; (2) tubes of too large diameter and too thin; (3) copper fire-box above the level of the water, and unprovided with safety appliances; (4) copper of too thin a gauge; (5) fire-door opening too weak; (6) supply-pipes not provided with expansion joints; (7) stay-bolts badly made; (8) cast-iron parts of bad design, or subject to unequal expansion; (9) plates of too low a grade for the strains to which they were submitted. Defective maintenance was the cause of fourteen accidents through: (1) corrosion of plates and other parts; (2) wear and deterioration of brass smoke-tubes; (3) wear and defective repair of a copper fire-box; (4) overstraining of a stay-bolt; (5) defective making of joints. Careless working caused fifteen accidents, viz., in five cases through shortness of water, and in seven cases through want of cleaning, in one case through an excess of pressure, and in two cases through tightening joints while under steam. In five cases the causes of the explosion were not ascertained. Further Tables classify the accidents according to: (1) the class of work for which the boiler was employed; (2) the type of boiler; (3) the presumed cause of the accident. The total number of accidents dealt with was forty-four, which resulted in injuries to twenty-five men and death to sixteen. Three Plates with fifty-four figures, showing details of failures, illustrate the Paper. H. I. J. The Application of Graphical Interpolation in Machine Design. A. S. OSTREICHER. (The Engineer, 28 October, 1898, p. 412.) In making graphical tables for machine elements it has been found expedient to sketch, roughly, the two extreme sizes and check the principal dimensions by calculation, correcting the designs accordingly. The principal dimensions of a size midway between the extremes can be readily checked by calculations; if these are not the mean of those of the extremes, the range between the limits is too large and is reduced till this is so. Then, all other intermediates can be found as follows: Draw out the design of the largest size, and draw a series of equidistant parallel lines to the axes of the drawing-as many as the number of consecutive sizes required. Project the important points on to the first of the parallels, and on the last lay down the corresponding dimensions of the smallest size. Join the similar points by straight lines, then the intersections of the latter with the other parallels give the dimensions of intermediate sizes. A. W. B. Tests of a Triple-Expansion Steam-Pump at the St. Gall Waterworks. A. STODOLA. (Schweizerische Bauzeitung, 1898, p. 54. 3 Figs.) The new pumping-station of St. Gall was set to work in the spring of 1895. The town being insufficiently supplied with water, a new source in the Bodensee was chosen, at a distance of 6.2 miles and a difference of level of 984 feet. In order to avoid impurities, the suction-pipe is carried out 436 yards from the shore into a depth of 130 feet to 150 feet of water. The whole plant was built by Sulzer Brothers, of Winterthur. The water is pumped through a pipe 446 yards long and 20 inches diameter, and delivered to the filters, whence it passes by gravity to the reservoirs. There is also a pump used for compressing air. These pumps are driven by a triple-expansion steam-engine, and space is left for an electrically-driven plant, which will be supplied with current from the waterfall at Goldach; this current will only be used for pumping from 10 p.m. to 6 a.m., while during the day it will be employed for the electric tramways of St. Gall. The tests referred to took place from the 25th to 30th March, 1898. The boilers were fired with coke from the municipal gasworks, and as the coke was largely in the form of dust, separate tests were made with the sifted and unsifted fuel. Details are given as to the methods of observation employed. An analysis of the coke showed combustible matter to be from 71.7 per cent. to 89.6 per cent., and ash 7.2 per cent. to 17.5 per cent. Analysis of the flue gases in three cases showed no CO, in one case traces, and in one 4.1 per cent. The general results are given in the form of a very complete table, from which the following details are taken: High-pressure cylinder, 14.1 inches diameter; intermediate cylinder, 23.75 inches diameter; low-pressure cylinder, 34.5 inches diameter; stroke, 39 37 inches; speed, 60 revolutions per minute. Boilers of the Sulzer tubular type, and Green's economiser, and a tubular superheater are used. The temperature of water from the economiser was 132° F.; flue gases before reaching economiser, 387° F.; after leaving it, 180° F.; steampressure, 150 lbs. per square inch; power developed, 210-5 I.HP.; work in water pumped, 169.88 HP.; steam consumed, 12.1 lbs. per I.HP. hour; coke consumed per pump-HP. hour, 1.6 lbs.; commercial efficiency, or the relation of pump-HP. to indicated HP., 81 per cent. E. R. D. Recent Progress in the Development of Pneumatic Dispatch Tubes. B. C. BATCHELLER. (Journal of the Franklin Institute, vol. cxlvi., 1898, p. 81.) After a short historical account of the introduction of pneumatic dispatch-tubes, the Author proceeds to describe the 6-inch and 8-inch tubes now in use in America for the carriage of mail. In these large sizes the weight of a carrier and its contents is considerable, and necessitates arrangements to stop it gradually. Small tubes, up to 3 inches in diameter, in use in London and elsewhere, are operated both by currents of compressed or by currents of rarefied air, but the American 6-inch and 8-inch lines are all worked by compressed air. If compressed air is used, and the pipes are laid underground, water will be kept out and not drawn in through any leaks. Air-cushions for checking the speed of the carriers at the stations are more efficient, and the gear operating the sending and receiving apparatus may be made smaller when compressed air is used. Owing to the reduction in temperature of the air, as it expands in the tubes, moisture is deposited, and in order to avoid this, as far as possible, the same air is used over and over again. The sending and receiving apparatus are to a large extent automatic, and in connection with the former a dash-pot is used to prevent the too rapid dispatch of carriers; the period varies from 6 seconds to 15 seconds, depending on the length of the line. Intermediate stations are arranged to automatically discharge carriers intended for them, but to allow all others to pass on. This is effected electrically, with the aid of different-sized disks, in the end of the carriers. The straight tubes are of cast-iron, accurately bored, and the bends of brass bent to a radius of twelve times their diameter. The speed of the carriers is very great, a line 3,000 feet long being traversed in less than a minute. The article is illustrated, and details of the location of a stoppage by measuring the time between the sound of an explosion and the ccho are given. W. B. Temperature in Deep Mines. J. STERLING. (Transactions of the Australasian Institute of Mining Engineers, 1898, p. 94.) The following results, showing the rate of increase of rock temperature, were obtained at Lansell's 180 Mine, Bendigo, Australia : The mean result of these ratios shows that the ratio of 1° F. for every 137 feet in depth is the record of the Silurian rocks of Bendigo. B. H. B. Results obtained in Driving the Sea Adit of the Bouches du Rhône Coalfield. (Comptes Rendus mensuels de la Société de l'Industrie Minérale, 1898, p. 179.) In the long drainage gallery which has been undertaken to connect the mines of Trets and Fuveau with the sea, near Marseilles, driving by means of electric boring machinery has been very successfully adopted. The rock traversed is Urgonian (lower cretaceous) limestone, sufficiently uniform and compact in character to admit of the use of rotatory boring machines, without requiring timbering or walling. The Bornet electric boring machine is used, taking the current from a dynamo driven by a turbine, the power being derived from a feeder of water encountered in the workings giving a pressure of 120 lbs. The same dynamo works a Mortier ventilating fan and the lamps for lighting the workings. The material broken in the face, which in June 1898 was 5 kilometres from the level mouth, is carried out by an endless rope haulage. The work is done in three shifts of 8 hours, seventy-six shifts, or 26 days having been worked in the month in question. The results obtained were Two volleys or rounds of shots are fired as a rule in each shift (178 in 78 shifts). The average time for each volley is 4 hours 4 minutes 42 seconds, divided as follows: Adjusting the machine in position Loading and firing. Time lost for smoke to clear : Removal of broken stuff Time actually lost. 0 21 1 0 36 0 2 33 The 153 volleys, in June 1898, required the boring of 1,791 holes, of a total length of 1828.7 metres. The average number per volley was 11.7 of 1.021 metre depth. Five hundred and thirty-two borers were blunted, or an average of three and a half per volley. The work is done by each shift independently; the distance driven is measured up, settled between the men at each change (any points in dispute being settled by the respective foremen), and premiums are awarded daily to the men who have realized the maximum quantity of work. H. B. |