206

DETAILS OP (PADDLE-WHEEL)

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ing gear.” The requisition of this gear is toraise or lower the slide valves without themotion of the cranks, or steam pistons. Now,with the motion as arranged, this is attainedby moving the link forward or backward asmay be required, and the fixed points of theeccentrics cause the valves to move simulta-neously. Many arrangements are made and

device, it is noticed, accomplishes the samefinal result, although the mechanical contri-vances are different.

In the example under especial notice andillustration, the arrangement is unlike anyother alluded to. The principle of the motionis a direct action, this being attained by arevolving screw and sliding cross bar. The

Fig. 46.

UHL

MESSES. WATT’S LINK MOTION AND STAETING GEAE FOE OSCILLATING ENGINES.

carried out to meet the requirements nowalluded to. In some cases the shifting rod isconnected to a lever, the latter being keyed ona weigh shaft, and motion imparted by a wormand toothed quadrant. In other instances, apinion and wheel have been preferred ; whilea third example dispenses with the wheel, andthe rod is connected to a shifting rack, thelatter being worked by the pinion. Each

side elevation shows the screw supportedin a frame at each end, with the startingwheel beyond the outer bearing. The crossbar is also shown, but more clearly in theplan of the gear. The connection with thelinks is attained by flat rods hung at eachend of the bar. In order to counteract thespiral action of the screw, and preserve adirect motion for the bar, two side guides are