STATIONARY ENGINES.

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steam-cylinder end being quite plain. The parallel bars are fittedto the crosshead and to the cross bars on the back links, the brassesbeing adjusted with a single key;the radius rods are similar, andwork on a pin fitted to a bracketwhich is secured to the springbeam at the cylinder end, andthe other eye takes the cross barfor the back links. In setting outthis parallel motion, the lengthof the links from centre to centreis one-half of the piston stroke;the centre for the back links on the beam is equidistant from the

Fig. 176.—Bracket for Parallel Motion.a, Bracket. B, Pin secured with nut.

The parallel and

end of the beam and the centre of Vibration,radius rods are exactly this lengthfrom centre to centre, or the dis-tance from the back-link centre tothe end centre of the beam; thetrue line of the piston rods beingone-half of the versed sine of thechord contained by the full arcdelineated by the travel of thebeam, taking the distance from theend centre to the centre of Vibra-tion as the radius.

The cold-water pump is a plainopen barrel, fitted with a suctionvalve of leather, stiffened withwrought-iron plates at the topand bottom, rivetted through andthrough, and hinged on a separateconical valve seat. A cross bar,having an eye at the top, is fittedfor holding down the leather, andfor drawing out the valve andseating; this is secured to thelatter by a cotter passing throughthe shank forged on the cross bar,the cotter bearing on the under side of the web cast along withthe seating. The bücket is fitted with a valve of a similar descrip-

Fig. 177.—Parallel and Radius Rods for ParallelMotion. — a, Parallel rod. b, Radius rod.