The Locomotive Of Today

16 The Boiler: Belpaire Firebox, Stijfening Rings, &c. As the bosses on girder stays hamper the rising of the steam bubbles, as well as take up a large portion of the heat- ing surface of the top of the box, and as direct stays, when connecting the flat top of the inner box to the semi-circular wrapper plate, are not always satisfactory, a form of box has been largely used in which these objections are removed. It is called the “ Belpaire ” from its originator, and is illustrated in Fig. 3; the outer wrapper plate is made flat on the top, and the inner one parallel to it, these are tied together by direct stays similar in character to those employed at the sides of the box, excepting that these top stays are usually of iron. The first two rows have means by which greater vertical flexibility is given to the front of the box, as before described for direct stays. Cross stays are also necessary for the flat sides of the outer wrapper above the inner box. Another advantage this box has is the greater facility afforded for cleansing the top of it, since side washing holes, as well as those at the back, can be put in if required. In good practice, on the inside of the boiler, a stiffening- ring or plate is rivetted round the holes cut in the barrel for the reception of the dorne and safety valve seating, as the cutting of the plate interrupts the true circular form, and weakens the boiler at these places. The chief features in the design of locomotive boilers are to make every part as easily accessible as possible, to facilitate the periodical cleansings such a boiler necessarily requires, and to provide for repairs being executed as cheaply and expeditiously as possible. The mode of fixing the boiler in the frames of the loco- motive next requires consideration. The front tube plate is continued down below the barrel, and rests on and is bolted to the back of the cylinder casting in inside cylinder engines, and to a distance casting and frame stay in outside cylinder engines, thus holding the boiler rigid at this end; but as the barrel necessarily expands when heated, the firebox end is carried by some arrangement of expansion links or brackets. The most common form of “expansion bracket” consists of an angle piece rivetted or bolted to the outer firebox shell about the level of the top of the frame. This angle rests and is permitted to slide on a level bed provided for it; it is kept in place and prevented from rising by a grooved block bearing lightly on its upper surface. The boiler is thus free to expand longitudinally; to steady it laterally, a plate may be secured to the back plate of the firebox with a stout pin projecting and engaging in a suitable socket prepared for it in the foot plate casting of the engine. Another method of securing- the