use. For high-pressure Lancashire boilers they are frequently used in combination with gusset stays, but in good practice they are, as a rule, applied to act more as a “stand by," to take their share of the strain in the event of any of the other stays failing. Longitudinal stays in all cases should be secured at the ends by substantial nuts and washers, both internally and externally, and except in very short boilers they should be supported by suitable rods or brackets rivetted to top of shell. Diagonal bar stays are inferior to gusset-plate stays, inasmuch as they do not support the ends in the same uniform manner, and are not so well adapted to resist the upsetting action due to the indirectness of the strain. Figs. 24, 25, 26, and 27 are illustrations of the ends of a Lancashire boiler fitted with gusset-plate stays suitable for a working pressure of 80 lbs. per square inch, and Fig. 28 represents the area supported by each stay. It will be seen that three of the stays are carried back to the second ring of shell plates, which adds considerably to their efficiency without interfering with accessibility to any great extent. The portion of the end plates above the flues requiring to be stayed is (as is usual) about one-third of the total surface, and the shell being 7 feet 6 inches diameter, there is thus an area of 2,120 square inches over which the stays have to be distributed. The strength due to the plates and their edge attachments is left out of consideration, and the stay section in this case has been made ample for the pressure to which the segment of the plates above the flue is exposed. The actual load on the plate is found by multiplying the pressure in pounds per square inch by the number of square inches in the area—viz., 80 × 2,120=169,600 lbs.; and as the strains to which stays are exposed should not exceed 5,000 lbs. per square inch of sectional area for iron, and 7,000 lbs. for steel, the total sectional area required by these stays is found by dividing 169,600 by 5,000 and 7,000 for iron and steel, which gives 34 and 24 square inches respectively. It will of course be understood that the rivet section at each end of the stay is greater than the gusset plates section at their weakest parts, marked N on Fig. 24. inch. In the illustrations the proportions are made out for steel, the thickness of the gusset plates being Stay A at narrowest part of web is 15 inches net. are 13 Areas for each Stay Stay A supports an area of 528 square inches. A x P where Pressure per square inch of stay section = A area to be supported, P = pressure, D pressure, D = depth of stay at weakest part, and t = thickness of stay plate. Then =6,332 lbs. per sq. in. of stay A plate section, 528 × 80 15 × 1 445 x 80 =6,260 13x Total area supported by gusset stays above the internal tubes is 528+ (445 × 2) + (350 x 2) = 2,118 square inches, or nearly of the whole area of end plate. Total sectional area of stays-A, 15.25 × 4375 6·67 B, 13 x 2 x 4375=11:37 As will be seen from the foregoing, the proportions of these stays are ample, the greatest strain being considerably under the allowable stress of 7,000 lbs. per square inch of section at the weakest parts. It may be argued that the outer stays, C, cannot support effectively the irregular area shown on the diagram, but the portions of the plate which might be considered outside the influence of these stays, are well supported by the shell and flue attachments, and are stiffened by the feed- and scum-pipe blocks which are usually rivetted at these parts. The gusset stays below the flues are proportioned somewhat similarly to the others; but owing to the man-hole opening, those at the front end cannot be placed so advantageously as at the back end. The plate, however, is stiffened by the compensating frame round the edge of the man-hole, and there being no necessity for a breathing space at bottom, such as there is at the upper sides, the angle irons can be carried much nearer the flues, and by this means the gusset plates can be made of sufficient depth. Gusset stays are often very imperfectly applied, the angleirons connecting them to shell and ends being slovenly fitted with bolts, and frequently set so as to leave more or less of an open space when the plates are inserted between them; the plates may also be found warped and bent into various forms owing to the stays not being arranged radially; and in addition to such defects in design and workmanship, instances are not wanting where the strength of stays, even if adequately fitted, is considerably under what is required, the result being that the attachments to shell and flues groove rapidly by the excessive springing of the plates. Grooving will also be caused by too rigid staying, such as occurs when the gusset angle-irons on the end plates are brought down close to the flue attachments. Referring to Figs. 25 and 26, it will be seen that there is a distance of 9 inches between the bottom rivets of the gusset stays, and the rivets at upper sides of furnace angle-irons. This space (commonly termed the "breathing space") admits of the plates springing to a moderate extent, and thereby prevents undue straining, such as is liable to occur through the greater expansion of the furnace tubes over that of the shell. With boilers carrying moderate pressures, the ordinary practice is to fit the gusset plates into the angle-irons after the end plates have been rivetted up-this method being |