298

DETAILS OF SCKEW ENGINES.

Messrs. Napier adopt, in some cases, thevalve and link nearly as those by Messrs.Fenn, at least if not in design, the same in

an elevation of the link and of eccentric rod,adjusting handle and quadrant. The con-necting rod is also shown at half stroke

Fig. 153.

MESSES. PENN’s EXPANSION VALVE AND GEAR.

principle of effect and arrangement. Thisanalogy will be better understood by alludingto Plate 28, where the gridiron valve, eccentric,and link, are all shown in sectional and com-plete views.

The firm next to be alluded to, who adoptthe arrangement under notice, is the Messrs.Rennie; but in the place of a gridiron valve,a circular, or rather tubular, perforated valveis preferred, with a seating to correspond.This example is illustrated by Fig. 154, andshows that two tubes—one within the other—comprise the valve and seating, and the differ-ence in the widths of the openings and solidportions between, produce the cut off requisite.The valve slides and derives its motion froman ordinary eccentric, and the change of thegrade of expansion is effected by a link andconnecting rod attached to the valve rod.Readily to understand the utility of thesedetails, will be to refer to Fig. 155, which is

within the slot in the link—the dotted lineson the quadrant depicting the utmost move-

Fig. 154.

v—

messes, rennie’s expansion valve and casing.

ment, effective or neutral, as required. Thelever, projecting above the link, is key®^