The Locomotive Of Today

104 Ihe Engine: Joy s A'alve Gear. the top end for the attachment of the valve rod end, and the other close to it for the pin, which carries upon its ends the quadrant blocks, which are fitted to sliding- curved guides fixed to the reversing shaft. It will be seen that the vibration of the connecting rod when the engine is running moves the quadrant blocks up and clown in the curved guides, compelling the valve rod to take a course dependent upon the position of the guides; thus, in the sketch the guides benig- vertical, the valve rod, and with it the valve, will have least movement horizontally, and the engine is in mid-gear.” When it is desired to run for- ward, the reversing shaft has a partial revolution given to it, tilting the top of the guides over towards the cylinders; this causes the block to move in the required direction and gear. When the engine is reversed to full back gear, the shaft is partially turned, so that the tops of the guides lay over towards thefirebox; the points of cut-off between mid-gear and full gear are settled by giving the guides more or less inclination as required. lo determine the several dimensions and positions ot attachment of the various rods, etc., it is necessary to take into account all the arrangements of the engine. The position of the pin hole in the connecting rod for attachment of the correctmg link is found by drawing lines from the points in the crank circle which the centre of the crank pin occupies when the piston is at half stroke to the centre of the small end pin, and taking a point in the leng'th of the connecting- rod which has a vertical vibration equal to at least twice the full stroke of the valve, so as to avoid too great an inclination upon the guides when the engine is put over into full forward or back- ward gear. This point being fixed, mark off upon the centre line of the rod the position it will occupy when the crank is upon its front and back centres respectively, and draw a vertical line vertical to the centre line of the motion—through a point exactly central between them. The length of the correcting- link can now be found; its end, which is attached to the anchor link, must be sufficiently far away to allow of the angle between its two extreme positions being less than a riø'ht angle. & Ihe anchor link should be made as long as convenient, so as to allow the end of the correcting link to rise and fali as nearly as possible in a vertical line, it will not affect the dis- tribution of steam which end of the engine its end is fixed, but it is usually found more convenient in locomotives to fix it forward of the crank.