The Locomotive Of Today

The Engine.- Reversing I^evers and Serews. 113 <equal to the travel of the nut, from which a pointer projects up and indicates upon a scale marked upon the face of the guard, the point of cut-off the gear is in. Another method of applying the screw is represented at C, in which the lever is dispensed with altogether, and the reversing rod coupled direetly to the nut upon the screw. The screw is cut with a coarse thread, as before, and carried in a pair of brackets, but instead of a wheel a pair of arms with handles set opposite to each other are employed. The handle at the top, in the illustration, is fixed to its arm and used to turn the screw, but that shown at the bottom is hinged and attached to a catch which it raises or lowers into notehes in a ring fixed to the screw bracket casting, to enable the gear to be secured in any position. A cover and index is fitted as in the last case. Many engines have an arrangement exaetly the reverse of the above, the screw being attached direetly to the reversing rod, whilst the nut, forming one with the boss of the wheel and being revolved with it, pulis or pushes the screw and reverses the motion from one gear to another. The lever has the advantage of being quickly moved from one full gear to the other, and, therefore, is especially suitable for shunting engines; its disadvantage is that the notehes, which have to be spaced widely for strength, frequently cause too great a difference in the rate of expansion when the catch is moved from one notch to the next, so that expedients are often resorted to by drivers to give a less difference, a common one being that of placing a piece of metal across the notehes so that the catch will bear against it and hold the lever in a. mid-way position. In the Norris lever, mueh used in the U.S.A., two catches are employed, one on either side of the lever, spaced to half a notch, and the catches being made with tapered ends, one or the other will always engage in the sector plate at half the travel of the plain lever. The advantages of the screw are the ease with which the engine can be reversed with steam on, and the great range of positions which it has. In order to quickly and easily reverse the valve motion many arrangements of reversing gears, working by steam or compressed air, have been devised. One of these, operated by steam, is shown at D. Upon the top of the trailing splasher, inside the cab, two cylinders, each about 5-in. diameter by 9-in. stroke are fixed, with pistons both secured to the same rod, so that they move togetlier. The cylinder shown on the right is for steam, and has the usual ports, one to each end of the cylinder and one to exhaust between them. Upon the port face is a flat bottom disc valve, revolved by 8