252

MODERN STEAM PRACTICE.

plate is laid down on the top of the foundation, having fittingstrips for correctly adjusting the vertical line of the cylinder, cor-responding strips being left on its base for that purpose. Thismakes a thoroughly good fixture, as these foundation plates spreadover a large surface of the stone or brick work, and the action ofthe steam in the cylinder and motion of the working parts havenot so much tendency to abrade the stone and loosen the founda-tions. The cylinder cover is generally an open casting, and shouldbe turned on the face; the surface is made steam tight by scrapingthe faces on the cover and cylinder, and interposing a thin coatingof red lead at the joint. A brass bush is fitted at the bottom ofthe stuffing box, and also in the cast-iron gland. The flange ofthe stuffing box has a raised part round the edge, to prevent theoil or other lubricant from flowing over and dirtying the cover.The cover is turned all over the exterior, and should be finishedbright, as it is then much more easily kept clean. The bolts forthe gland should be cut with a square thread, and have square nuts,as hexagonal nuts are not nearly so good for parts requiring suchfrequent adjustment.

The piston is of the usual description, and made very heavy;

Fig. 153.—Piston for Steam Cylinder.

A, Coned part for the piston rod. b, Junk ring, c, Metallic packing ring.

indeed, some engineers cast the body solid, with a view to balancethe large blowing piston at the other end of the beam. The pack-ing ring should be in one piece; some use two rings, but this is notrequired, and is decidedly objectionable, from the fact that there arethen four faces to be kept steam tight, whereas with one ring thereare only two. The narrow junk ring is accurately turned on thefitting strips and corresponding parts on the piston, and is madesteam tight by scraping the surfaces. The holding-down bolts arescrewed into nuts recessed into the body of the piston in the usualmanner. The piston rod is secured to the piston by means of aconed part turned on the former, with a corresponding cone on thelatter, through which a cotter passes and tightly forces the pistonon the coned part of the rod. A better plan is to fit a nut on the