The Locomotive Of Today

The Boiler: Stays. 11 extreme end of the round stay, or with an ordin ary tap wrench taking a square head, made on the stay for this operation and afterwards cut off. When screwed in the stay should stand with about of an inch projecting through both plates, inner and outer ; this projection is hammered down to form a head and to ensure a good steam tight joint. The above methods refer chiefly to copper stays, as shown at A, Fig. 2, or to wrought iron when used; with the Steel ones, now adopted on several English railways, it is customary to drill a hole of say f-in. diameter into both ends of the stay about i-in. or 1 j-in. deep, as shown at B, so that the ends can be expanded in the plates by hammering a hard Steel drift into these holes. With Steel stays the screwed threads are turned off the middle portion and the diameter reduced to secure greater flexibility; copper stays are usually screwed their entire length, but under- cut along the middle portion to ease the threacl. Recently stay bolts of phosphor bronze, with longitudinal saw cuts at right angles down the central part to secure flexibility, have been introduced with success. The stays may be -J-in. or i-in. diameter, and if pitched 4-in. apart, each will support 16 sq. in. of plate at each end. Some makers drill a small hole through the longitudinal centre of the stay, so that should one break the steam and water will escape through it and give warning; without this hole the stay breakages can only be detected by tapping with a hånd hammer on the ends and carefully noting the sound. Examiners accustomed to this work get so skilful that they rarely pass a defective stay. When it becomes n^cessary to take out the inner firebox all the stays must be removed, either by drilling, punching, or tearing out with pneumatic or hydraulic tools ; in any case the screwed holes, especially in the copper plates, are liable to damage and require re-tapping, it is thus seldom possible to use stays again of the original diameter, and they are usually replaced by new ones of larger size. In renewing broken stays with the boiler in position, it is not possible to get at the outside ends of those immediately behind the frames or tanks to rivet them over, and the stays must therefore be screwed in a very good fit to get a steam right joint. In screwing in, this tightness imparts an initial torsional strain to the stay, which may prove detrimental to its life. Copper stays possess many advantages over their wrought iron and Steel rivals, as not only are they admirably suited to the various twisting strains that the expansion and contraction of the two fireboxes subject them to, but the superior heat-conducting properties of copper are greatly in its favour when used for this purpose.