Appleton's dictionary of machines, mechanics, engine-work, and engineering . is yielded by the box-link; the block may be shifted to a position levelwith the point of attachment at which it may transmit the whole throw of the eccentric. The over-hung nature of this knuckle-jointed sort of link, and its peculiarly irregular movements in consequence,render it a more ticklish variety than the others; as, however, it combines the advantage of the box-link in respect of the transmission of the whole motion, with the simplicity of the other link, it is nowmost commonly employed, at least in locomoti
Appleton's dictionary of machines, mechanics, engine-work, and engineering . is yielded by the box-link; the block may be shifted to a position levelwith the point of attachment at which it may transmit the whole throw of the eccentric. The over-hung nature of this knuckle-jointed sort of link, and its peculiarly irregular movements in consequence,render it a more ticklish variety than the others; as, however, it combines the advantage of the box-link in respect of the transmission of the whole motion, with the simplicity of the other link, it is nowmost commonly employed, at least in locomotives, where vertical clearance is limited. The first qualifications of expansion gear are to insure for every variation of expansive action, a freeadmission and free release for the steam; to render the periods of admission equal for the front and back LINK-MOTION. 231 strokes, and to promote the expansive action of the steam sufficiently to extract the most if not the whol«of its works for propulsion, excepting a per centage required for the purposes of the hlast. Lead. In the stationary link-motions, a constant lead throughout the forward and hackward geaiis ohtained by circling the link to the radius of the valve-rod link, and the same lead may he for thefront and hack strokes. In the shifting link motion, the lead essentially varies with the expansion, thegreater the degree of expansion—that is, the less the admission the greater also is the lead; the leadis thus least in full gear, and attains its maximum in the mid gear; it may however always he made thesame for the front and back strokes, and thus equality is obtained by circling the link to the radius ofthe eccentric rod. Thus the conditions of constant lead and varying admission which are incompatiblewith the nature of the shifting link, motion are obtainable by the stationary link with a single longer the eccentric-rod, and the shorter the link, the less is the variation of lead in the shifting-link
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Keywords: ., bookcentury1800, booksubjectmechanicalengineering, bookyear1861
