(143.)

That part of Cartwright's piston which in the common piston is occupied by the packing of gasket, already explained (141.), was filled by a number of rings, one placed within and above another, and divided into three or four [Pg248] segments. Two rings of brass were made of the full size of the cylinder, and so ground as to fit the cylinder nearly steam-tight. These were cut into several segments A A A ( fig. 67.), and were placed one above the other, so as to fill the space between the top and bottom plates of the piston. The divisions of the segments of the one ring were made to fit between the divisions of the other. Within these another series of rings, B B B, were placed, similarly constructed, so as to fit within the first series in the same manner as the first series were made to fit within the cylinder. The joints of the upper series of each set of rings are exhibited in the plan ( fig. 67.); the places of the joints of the lower series are shown by dotted lines; the position of the rings of each series one above the other is shown in the section ( fig. 68.). The joints of the inner series of rings are so placed as to lie between those of the outer series, to prevent the escape of steam which would take place by one continued joint from top to bottom of the packing. The segments into which the rings are divided are pressed outwards by steel springs in the form of the letter V, the springs which act upon the outer series of segments abutting upon the inner series, and those which act on the inner series abutting upon the solid centre of the piston: these springs are represented in fig. 67.

Fig. 69.