REGULATION OF STEAM.

US

quite flat, while the other is circular. The' former is simply a flatplate, having a number of slots or openings, strengthened with ribscast on the back; the valve is of brass, as likewise is the face it worksupon. It is placed as near to the main slide-valve as possible. Thereis a considerable steam pressure on the flat type, and to obviate that

f

Fig. 62.—Expansion Valve Gear.

a b, Line of crank, c, Valve ehest . d e, The radius of expansion link. f, Lever end for ditto.

G, Centre of eccentric at the begirming of the stroke.

defect circular valves have been introduced, one species being inequilibrio, consisting simply of a series of rings and openings cast allin one piece, and having a central boss with ribs radiating from thecentre. These ribs hold all the rings together, the openings beingI inch broad for large valves; five of these openings have beenadopted, giving ample area. This valve is accurately turned to fit asimilar cylinder of brass, with openings to correspond, held togetherwith vertical ties, cast all in one piece—the whole being encased in acast-iron valve box, having an annular space all round. The steamfrom the boiler passes down through the hollow valve, and then roundthe annular space into the slide-valve ehest on the cylinder. At thecommencement of each stroke the ports are full open, and the valvegear is so arranged as to cut off up to a little more than one-half ofthe stroke; at least, practically speaking, this is attained (while theslide-valve for the engine is arranged to cut off at five-eighths of thestroke of the pistori). The valve gear consists of an eccentric,having a throw of 2 inches, the eccentric rod taking a lever 4 inchesin -length. This lever vibrates on a short shaft, on which is fitted aslot link with a movable sliding block, to which is attached the con-