The Locomotive Of Today

172 The Tender, Brakes, etc. : Brake Gear, Brake Blocks. new ones may be fitted and the nut slacked back to its original position. At A and B the arrangement and positions of the various parts may be traced, being shown in elevation and plan. O wing to the faet of the firebox being direetly above the shaft in this example, it is not possible to place the hånd gear there, so an arrangement of beil cranks and levers is shown, by means of which it can be moveel further back to a convenient position in the cab. On some engines the shaft itself is carried well back, and the pull rods lengthened to suit; on others the brake blocks are made to bear upon the couplecl wheels opposite each other —that is, the leading couplecl wheels will have blocks upon their front, while those upon the next couplecl wheels may be upon the back, or the hangers and blocks are in some cases both between the wheels, the blocks being pressed outwards away from each other. Neither of these methods are to be preferred to that shown as they both tend to throw stresses upon the coupling rodswhen applied, the former by compression, the latter by tension. In many other designs blocks bear upon both sides of the wheels at the same time, but this is not always necessary, as one block well applied is sufficient. Slotted holes are provided in the pull rods from both the power cylinder and the hånd gear, so that when one of these is used to apply the brake the pin of the other lever simply travels in the slot; all the wrought iron wearing surfaces are well case-hardened to reduce the wear as mueh as possible, and split pins or cotters are used to prevent the pins, etc., from slacking back. Brake blocks are usually of cast iron and being of softer metal than the Steel of the tyres, they therefore take most of the wear, being easier to replace when worn out. The proper length of block is between i -ft. and i-ft. 6-in.; if made less, it is liable to get very hot when applied hard. No advantage is secured by exceeding this length, as blocks which are too long and are applied at the centre have a tendency to bend, only bearing hard opposite the point where the pin is situated. To use softer cast iron, which alone would not have sufficient cohesion to stand the rough wear for long, blocks are now extensively made of iron cast upon inserts formed of several layers of expanded Steel closely packed and interlaced with each other. These hold the particles of iron up to their work, and greatly inerease the life of the blocks as well as the friction and consequent retarding power. They are known as the Sargent patent diamond brake blocks. Compositions of various kinds are also being triecl, forced