LOCOMOTIVE ENGINES.
59 1
notice the eccentrics are of cast iron, and the strap and rod ofwrought iron. The link is of the double description, rivettedtogether and suspended with two hanging links from a bracketsecured to the boiler. The
connecting link is forked atone end, taking a crosshead,
which works in suitableguides. The sliding block isof course double, made inone piece, with a part cut outat the middle for the end ofthe connecting lever held in
Position with a pin passingthrough the block. There is
a boss on the lifting link, a
short distance from the end that takes the sliding block for securingthe link for the up and downward motion. In some examples ofvalve gear it may be necessary to bend the valve rods and eccentricrods to clear the axles; this may be arranged as delineated.
A modification of the link motion more recently introduced isillustrated by Fig. 452. The expansive link is straight; the sliding
T
E D
Fig. 452.—Straight Link Motion.
a, Eccentrics. b b, Eccentric rods. c, Straight link, d, Connecting link.F., Connecting link, f, Radius rod.
block is carried on a radius link, placed between the main link andthe valve rod; both are connected to a long and short lever onthe weigh shaft, so arranged that the one travels up and the otherdown, and vice versa, meeting each other at half lift, the greatestvertical motion of each being only about half of that given to otherlink motions. Single eccentrics have been used for each valve,the reversing and expansion motion being obtained by means ofspirals and wedges. Figs. 453 and 454 give a general idea of thearrangements; the angular position of the eccentrics being al-