Dome and Safety Valve Seating. The dome L (Fig. 2), is formed of a small plate bent into a ring, the joint being either riveted or welded. It is flanged at the bottom in a press by means of blocks made to suitable shape. The flanged portion fits on to the circular barrel plate of the boiler, in which a circular hole has been made, and is riveted to it. The dome cover is a dished plate which is pressed into shape between blocks in a press, or sometimes under a steam hammer. The cover is secured to the dome, which has a faced flange or angle iron ring for the purpose, studs with nuts being used so that the cover can be removed when required. The safety valve seating and cover M are made in a similar manner.
After the boiler has been riveted up, the seams or joints are caulked. This is a process for making the joints thoroughly steamtight and preventing leakage, and consists in burring up the edges of the plates with a tool in the form of a chisel with a broad blunt edge. Care must be taken not to use a thin or sharp edge on the chisel or the plates will be injured and their edges forced apart. Caulking which was formerly done by hand, is now done by pneumatic hammers.
Inside Firebox: and Stays. The inside firebox N (Fig. 2) is of copper plates. These are planed at the edges, and the rivet and stay holes are marked off and drilled in the same manner as in the steel plates of the boiler and firebox shell. The
