The Locomotive Of Today

20 1 he Boiler : Tube Ends and Materials, Serve Tubes. of the latter, they frequently have a length of brass or copper, about 6-in. or g-in. long, brazed on to them at the firebox end in order to make a better joint in the copper tube plate. With copper, brass, or compound tubes, the joint in the firebox tube plate is made by expanding the tube in the hole prepared for it, beading the end over and driving in a Steel or malleable cast iron ferrule to protect the end of the tube from the action of the fire (G). A-Vhen the tubes areof steel or iron through- out, it is usual to swage down the firebox end to a less diameter than that of the length of the tube, and expand them in the holes, which will, of course, be of smaller size than in the last case, and bead them over, the ferrule being dispensed with (H). The smokebox end of the tubes is belled out to about 1-in. larger than the tube for about 3-in. of its length; it is expanded in the tube plate, but is not ferruled or beaded over (I). The enlargement is made in orcler to get the tubes in easier, and to facilitate removal when coated with scale; it necessitates the tubes being spaced slightly different at this end than the other. The tubes generally project about T3^-in. through the tube plate at each end before beading clown. Carefully conducted experiments and the results of actual practice show that after a few week’s work, with ordinary impure water, there is but little difference in the evaporative power of copper, brass, iron, or steel tubes, although their relative conducting powers are 74, 24, 12 and 13. Tubes of the more expensive metals keep cleaner on their external surfaces than iron or steel, due probably to their more rapid expansion and contraction throwing off the scale ; but when of copper, they are too soft to resist for long the abrading action of small cinders. As the hot gases pass through the tubes it follows that the layers of them that are on the outside will give out most of their heat, but through the middle of the tubes a considerable portion of the heat will pass to the smokebox unused ; several means of utilising this heat have been devised, and most notable of these is the “ Serve ” tube, which having- longi- tudinal internal ribs, increases the internal heated surface some 90 per cent., slices up the gases, and abstracts the heat from the centre. K gives a section of this tube. Good results have been obtained with these, although the use of them means a reduction in the number of tubes, as they are made larger than ordinary plain tubes, being 2-in. and more in outside diameter; further, the spaces between the ribs afford a good lodgment for soot, and consequently there is difficulty in keeping them clean.