404

MODERN STEAM PRACTICE.

distinguished from all other pistons of this dass by effecting theendwise and outward pressures by separate springs, each exactlysuited for the work they have to perform. As I have shown, thepressure of the packing rings endwise should be strong, and theirpressure outward against the cylinder light, or exactly the reverseof what occurs in all other double packing ring pistons.

“ The springs are extremely simple in their character and con-struction. They are made from light hoop spring Steel, varying inbreadth and thickness to suit the diameter of the piston. Breadthsfrom inch to 2 inches, and thicknesses from T V inch to T V inch,will serve for pistons from I to 6 feet in diameter. To oneseeing them for the first time these springs look quite inadequate toaccomplish the ends proposed. It is surprising to see a spring of

Fig-s. 287 a, 287B.— a, Junk ring, b b, Packing rings. C, Spring, d, Flange on piston.e, Part where the packing rings are cut.

a few pounds weight in a large piston accomplishing an effectto obtain which in other pistons continuous springs weighing severalhundredweights are used.

“The spring for pressing the packing rings against the junk ringand piston flange is bent round on its flat to the required diameter,and may have projections on either side alternately at definitedistances apart, or the projections may be similarly placed on thecontiguous faces of the packing rings, between which these springsare placed. The preferable mode, however, and that usuallyadopted, is to have the projections on the spring itself in the formof waves, as shown in Figs. 287A and 287B, and where they areshown in position between the two packing rings. It is found thatsprings made in this manner to definite proportions of height andlength of waves, now fully ascertained for all dimensions, can bemade to give an almost unlimited pressure when screwed to re-quired position, and the elasticity remains good for years.