The Cowles it Boiler.—The Cowles boiler (Pig. 13) is one of a numerous class of boilers recently designed to combine great steaming capacity, at the highest steam pressures, with the minimum weight of structure and water contained, and minimum space occupied. Obviously this combination can be obtained to the highest degree in what is known as a coil boiler, which consists of simply a mass of coils of iron or copper tubes of small diameter, and a furnace underneath them. Such coil boilers, however, arc usually defective in durability, and are apt to produce steam of varying quality, sometimes wet and sometimes superheated to a higher degree than is desirable. 'The coil boiler has therefore been modified in the direc tion of the water-tube boiler, supplying it with one or snore water and steam drums; and while retaining the small diameter of tubes. they are not made into continuous coils, but are made in separate short lengths, each of which is connected with the water-drums, and is easily replace able in case of burning out. The chief field for boilers of this kind is in marine work, where high speeds and light weight are required, especially in torpedo-boats and in racing yachts. Several varieties of this type of boiler have been built, as the Thornycroft, Herreshoff, Ward, Mosher, and Cowles. Detail drawings of some of them, and records of tests made by engineers of the U. S. Navy, are given in the Report of the Chief of the Bureau of Steam-} ngineering for 1S90. The Cowles boiler is selected here as a representative of the general type. It is de scribed as follows by its patentee, Mr. William Cowles, of Brooklyn, N. Y.. and consists of a rectangular grate and ash-pan, over which is set horizontally a cylindrical shell for steam and water; from the back part of this shell a steam-drum projects hack horizontally• from its front end large "downcast" pipes extend down to large side pipes at each side and below the furnace; these side pipes connect at their hack ends with the water-drnms lying horizontally back of the furnace and below or at its level ; numerous bent water-tubes, with ends expanded in, extend vertically and connect between the water and steam drums and between the side pipes and shell. The whole is inclosed in /l ellitably lined casing for marine use and in masonry for stationary work.
14, 15, 16. and 17 illustrate the boiler designed by Mr. C. It. Mosher for the fast steatn-lanuch Norwood, owned by N. L. Munro. of New York city. It has several novel features. For the power the boiler has to furnish, it occupies but a very small space, and its center of gravity is very low. It has ;20 sq. ft. of grate surface, and about 1,000 sq. ft. of heat ing surface. The tubes are made of steel, I in. diameter, solid drawn. The weight of the boiler and water is ;2i tons; its length is 7 ft. 8 in.; breadth, 0 ft.; total height, 3 ft. 6 in. Fig. 14 represents an end elevation of the boiler ; a portion of the easing is removed to show the interior. Fig. 15 represents a horizontal section taken on line 2, 16. Fig. 16 represents a transverse section on line 3, 3, Fig. 14. Fig. 16 represents a vertical section on line 4, 4, Fig. 16. The same letters of reference indicate the same parts in all the figures. In these illustrations a a represent two horizontal water-drums, which are arranged parallel with each other at opposite sides of the furnace b ; these drums arc placed just ;hove the grates c. The furnace, as will be seen by referring to Figs. 14 and 15, is divided into two sections by an interme diate water-drum a', and a row of tubes, f extending upwardly from the drum a', and arranged so that above their bent ends they form a close wall extending lengthwise of the furnace ; the upper portions of the tubes are curved outwardly ; every alternate tube extends over to the steam-drum at the one side of the furnace, and the remaining tubes over to the steam-drum at the other side of the furnace. The intermediate drum
a' is connected by transverse pipes a' with the outside water-drum a a, so that water from the drums a a enters the drum a', and passes upwardly therefrom through the tuebs f'. The tubes f 3 are connected with the transverse tribes a': they extend up ward. and are bent at their upper ends. and joined to the steam-drums d d. These tubes, spring from the pipes a' in two rows. Those of the outer row are bent in wardly, us shown at 14, Fig. 17, so that the tubes constitute closed vertical end-walls, the front one being interrupted by the spaces for the fire-doors. The steam-drums d d are placed above the water-drums is a, and are practically outside the space which constitutes the furnace. They asre arranged to bring their outer sides in a vertical plane with the outer sides of the water-drums to accommodate the casing e, which incloses the whole apparatus. Each water-drum is connected with the steam-drum by a series of bent steam-generating tubes, f, From the points of connection witri the water-drums, these tubes are bent wardly and upwardly toward the center and upper portion of the furnace. They are then bent outwardly until they juin the inner sides of the steam-drutns.
It will be seen that the tubes f, f, ffi, are formed and arranged to expose their contents in a favorable manner to the heat of the furnace, and at the muse time enable the steam drums d to be located at a minimum height above the water-drums a, thus giving the gener ator a low center of gravity. and making it its this respect desira ble for steam launches and yachts, in which economy of vertical space is desirable. The arrange ment of the inner tubes!' is such that these tubes along the for wanl portion of the furnace, or fire-door end. nearly to the oppo site end. constitute a practically closed wall, made up of the in clined portions of the tubes. The lower end of every alternate tube f is bent, as shown at 8, Fig. 16, so that the whole form two inner rows at the points where they join the water-drums, and come in close contact with each other just above the bend J. The object of arranging the tubes to form a close wall, as described, is to cause the heated products of combus tion to pass from the front toward the rear end of the furnace be fore passing to the outside of these tubes. To enable the pro ducts of combustion to pass to the outside of the tubes, a number of these tubes at the rear end of the furnace are made straight, as shown in Figs. 14, 16. and 17, creating the spaces 10 between the tubes)" and the intermediate tubes f. The spaces 10 permit the products of combustion to pass out wardly, as indicated by the arrows in Fig. 17, into the rear portion of the space between the walls 'composed of the tubes f and an outer wall composed of the tubes f placed next to the inner easing k. The lower ends of the tubes are marked 12, 13. in Fig. 1G. The wall composed of the tubes extends the entire length of the furnace. The spaces between the inner and outer walls of tubes contain the tubes which are of the same general form as the tubes f and ft but are separated, so that the products of combustion pass freely around each tube. With this arrangement the steam-drums are protected from the direct action of the fire by the interposed tubes, and um be affected only by the radiation of heat from the hot gases that pass through the spaces 10 at the rear portion of the firebox; hence, the liability of burning or injur ing the drums by overheating is re duced to a- minimum. As an addition al protection to the steam-drums, the partitions k k. previously referred to, are interposed between the lower por tions of the steam-drums and the fur nace; these partitions lie close to the wall formed by the tubes ft as shown in Fig. 16.