The amount of the taper varies considerably in practice. When the tapered part is long, the taper or variation in the diameter may be 1 in 24. When the tapered part is short, the taper may be as much as 1 in 4. The smaller the taper the more firmly can the piston, but it is the more difficult to remove. method of securing a piston-rod to a steel piston. FIG. 570. rod be secured to the Fig. 570 shows Kirk's CHAPTER XIX. STUFFING-BOXES. 265. A Stuffing-Box is used where a sliding or rotating piece passes through the end or side of a vessel containing a fluid under pressure. A The stuffing-box allows the sliding or rotating piece to move freely, without allowing any leakage of the fluid. Applications of the stuffing-box are found in the steam-engine where the piston-rod passes through the cylinder cover, and where the valve spindle passes through the valve casing; also at the trunnions of the cylinder in an oscillating engine, and where the shaft of a centrifugal pump passes through the pump casing. Stuffing-boxes are also used to permit of the expansion and contraction of steam pipes. Fig. 571 shows an ordinary form of stuffing-box for the piston-rod of a vertical engine. AB is the piston-rod, CD a portion of the cylinder cover, and EF the stuffing-box. Fitting into the bottom of the stuffingbox is a brass bush, H. The space around the rod AB is filled with packing, of which there are a great many kinds, the simplest being greased hempen rope. The packing is compressed by screwing down the gland LM by means of the bolts P. When more than two bolts are used, the gland flange is generally circular, as shown in the lower part of Fig. 571, but for three bolts it is sometimes triangular, and for four bolts it is sometimes square, the bolt holes being near the corners of the triangle or square. For two bolts the gland flange is generally of the form shown at (a) Fig. 572. When the gland is made of cast-iron, it is lined with a brass bush as shown in Fig. 571. When the gland is made of brass, no liner is necessary, and it then has the form shown at (b) Fig. 572. When heavy glands are made of brass, they may be lightened in the manner shown at (c) Fig. 572. 266. Proportions of Ordinary Stuffing-Boxes and Glands.—From the examination of a large number of stuffing-boxes and glands, we find that their proportions vary very much, even in cases where the conditions under which they work are the same. We believe, however, that the following rules will be useful, as they are based on the averages of a great many examples from actual practice. The letters refer to Figs. 571, 572. =d+ 1. l3 = '75l,= '75d + ·75. in. t='04d + 2, but not to exceed d = diameter of bolts = 12d + ·5 when two are used. For n bolts da (·12d + ·5), where n is greater than two. 1.6 In 267. Example of a Large Inverted Stuffing-Box. Fig. 573 shows an example of a stuffing-box used on a large marine engine with inverted cylinders of the type to be found in large ocean steamers. The stuffingbox is cast separate from the cylinder cover, to which it is afterwards bolted. The lubricant is first introduced to the oil-boxes, from which it passes to the recess underneath, where it comes in contact with the piston-rod. To prevent the lubricant from being wasted by running down the rod, the main gland is provided with a shallow gland and stuffing-box, which is filled with soft cotton packing, which soaks up the lubricant. The main gland is screwed up by means of six bolts, and to prevent the gland from locking itself in the stuffing-box, it is necessary that the nuts should be turned together. This is done in a simple and ingenious manner. One-half of each nut is provided with teeth, and these gear with a toothed wheel which has a rim only; this rim is held up by a ring secured to the main gland as shown. When one nut is turned, all the rest follow in the same direction. 268. Stuffing-Box for Oscillating Cylinder. In ordinary cases the lateral pressure of the piston-rod on the gland and stuffing-box is comparatively small, but in oscillating engines the swinging of the piston-rod is communicated to the cylinder through the gland and stuffing-box, and when the cylinder is large and consequently heavy, there is considerable lateral pressure on the gland and stuffing-box. This necessitates a greater depth of stuffing-box and gland to give sufficient bearing surface. An example of a stuffing-box for a large oscillating engine made by the Q |