The Locomotive Of Today

106 The Engine : Joy’s Valve Gear. In some small locomotives with outside cylinders, where it would not be possible to find room for the anchor link in the position shown in the illustration, the correcting links are cut off at the point of attachment of the valve levers, and the anchor link, coupled to them there, and at its other end to small return cranks upon the crank pin—the stroke of which must, of course, equal the distance travelled by the other end of the anchor link. Deviations from the above positions and proportions maybe made without materially altering the correctness of the results. The metals employed are usually wrought iron for the links, rods, pins, etc., the wearing portions being well case- hardened. The quadrant block guides too are of wrouglit iron, being usually turned up and cut from a large ring of the necessary radius and case-hardened. Ihe quadrant blocks are of bronze or cast iron, if of the latter, to prevent wear they are cast in chilis and ground up to shape. The reversing shaft is of cast Steel, and the bushes in the connecting rods of phosphor bronze. For the “ Joy ” gear many advantages are claimed—it is simple in construction and maintenance, the dead weight of the whole is less, and it is generally more correct in working, as, if the centre lines of the various levers, etc., are properly set out, a valve path diagram is given, in which the lead and cut-off are exaetly equal for both ends of the cylinders, and they remain so for all grades of expansion to mid gear. Ihe. valve opens more rapidly than when actuated by link motions, the cut-off being prompt and the release of the exhaust quick, whilst it moves slowly during the expanding and exhausting periods. These qualities are very desirable for a locomotive slide valve, when obtained without any undue lead, compression, or too early exhaust. Ihe cut-off point is not limited by the throw ofeccentrics, etc., but the reversing depends upon the angle to which the quadrant block guides are inelined, so that it would be only necessary to allow these to be carried over past the point usual for a full gear cut-off of, say, 75 per cent, to obtain a cut-off of 80 or 90 per cent. ; thus the starting power of the engine can be greatly inereased, and the trouble sometimes necessary of reversing to get it into a more favourable position dispensed with. lo set the valves in the shop, the four dead centres of the crank are found in the same way as for link motions, as also are the cut-off points for each port. Then setting the engine upon one dead centre, the rods being coupled up, the motion is reversed from one full gear to the other, if the valve spindle