Example of piston fitted with segmental ring

Example of piston fitted with segmental ring and wedge packing 8 1/2" diam.

This is a piston fitted with a modern form of the metallic packing patented by John Barton in 1816; it embodies improvements patented by Messrs. R. and C. H. Allen and W. J. Wakefield in 1900. The piston has two grooves turned in it, and in each of these a ring, formed of three cast-iron segments, is placed. The adjacent ends of the segments are bevelled, and between them are placed wedge pieces, which have turned stems fitting into holes in the piston, and are pressed outward by helical springs so as to expand the rings. The wedge stems are of larger diameter than the width of the rings, and they are carried up on each side of the inclines, level with the apex, so that a large surface is presented to the cylinder and scoring is prevented. A shallow groove is turned on the surface of each ring, and the segments in the two rings are arranged to break joint; the wedges have an angle of 125 deg. The example shown is 8.5 in. diam.