A packing-gland is a sort of flanged tube, which so fits a slide-valve rod or a piston rod that it can be easily slid along the rod. Glands are made of either gun-metal or cast-iron, and are employed to squeeze the packing tight around their respective rods, and to maintain it in this condition during the to-and-fro motion of the rods while at work ; by which means a steam-tight joint or a water-tight joint is secured. The packing is a pliable material, consisting of hemp or india-rubber; and it is this which grips the rod, but not the gland, which is always loose. The simplest mode of using packing consists in placing it between the extremity or bottom of a gland and the bottom of the packing-box, nothing being put between the packing and the bottom of the box.

In Plate 80 several classes of packing-glands and other packing apparatus are represented. The simplest class of glands are those denoted by Fig. 984; these are used for small engines, pumps, and other machines having rods not more than about an inch in diameter. The flange portion of the gland is hexagonal, and fits a spanner, by means of which it is screwed into its place in contact with the packing. The portion which is screwed is named the stem, and in Fig. 985 the extremity of the stem is shown, which is the surface to be in close contact with the packing. The gland denoted by Fig. 986 is employed for both small rods and large ones. This is furnished with an oblong flange having a hole at each end. These holes admit two studs, which are the means of squeezing the packing around the rod, instead of screwing the gland in with a spanner on the flange. The stem and dish-shaped extremity of the gland is shown by Fig. 987, which is analogous to that seen in Fig. 985, and acts in the same manner. A circular flange is sometimes adopted, instead of an oblong one, as indicated in Fig. 988 ; such being furnished with three or four holes for the packing-studs.

Plate 80

All flanges of glands should be curved at their corners or junctions with their stems, to obtain strength without making the flanges too thick. A curved corner of this shape is shown in Fig. 989.

The glands denoted by Figs. 985, 987, and 988, are situated in their packing-boxes in the positions denoted in Figs. 990, 991, and 998. The packing-box is a tubular portion that extends from the cylinder-lid, or other lid, and is cast solid with it. In the bottom of the box is a hole to admit the piston-rod, and above is a larger space, the diameter of which is about the same as that of the stem belonging to the gland. In this space is situate the packing wrapped around the rod, the dish-end of the stem being in contact. If a screwed gland like Fig. 985 is to be used, the hole in the packing-box is screwed to fit; but nearly all glands for rods an inch in diameter, or larger, are provided with plain cylindrical stems; and are consequently forced into their packing-boxes by means of screw studs. A gland with two studs is shown by Fig. 991, the studs being screwed tight in the flange of the packing-box, and of suitable length to allow them to extend a short distance beyond the flange at the time the stem enters the mouth of the box.

Fig. 998 represents a mode of forcing the gland into the box by means of loop-bolts instead of studs. In this arrangement a flange solid with the box similar to that of the gland is not admissible, room being required for the bolts. The loops of the bolts are connected by being placed upon short studs extending from the box; or they may be connected by short screw-bolts having plain parts adjoining the heads to fit the loop-holes, and having short screwed ends to screw into the packing-box. To obtain a proper amount of metal around these bolt-screws a couple of small bosses may be cast solid with the box similar to that shown in Fig. 999.

In Fig. 998, the situation of a rod in the gland and packing-box is also shown, being indicated by dotted lines. A packing-bush or garnisher, is also shown by dotted lines. This is of gun-metal, and situate at the bottom of the box and around the rod, the flange of the bush being in contact with the bottom and its stem extending through the hole. By this means the india-rubber or other packing is prevented from touching the bottom, and is caused to rest on the flange of the garnisher, a surface of gun-metal being thus provided for the friction surface of the rod, because the stem of the bush fits the hole in the bottom, which hole is larger in diameter than that of the rod. The diameter of the flange of a packing-bush is the same as the diameter of the stem belonging to the gland, both being made to loosely fit the hole in the box.

Figs. 996 and 997 are comparative large sketches of a gland-stem and its accompanjdng bush, the bush being shown by Fig. 997. In each Figure the dished or cup-shaped extremity is shown, by which it may be seen that the thin rims of metal around the dishes are of suitable shape to be wedged between the packing and the sides of the packing-box; consequently, when the gland is forced upon the packing, it is not only squeezed together, but also, to some extent, wedged away from the side of the box, and into close contact with the rod, by which the desired steam-tight joint, or water-tight joint is obtained.

For some varieties of very small rods, glands are made without any cup-shaped ends, the extremities which bear upon the packing, being flat and square to the stems. These flat surfaces require a comparative great amount of forcing with the gland-nuts, or with the six-sided flanges, and therefore involve a large amount of squeezing together of the packing to obtain the necessary grip around the rod; consequently, glands having flat bottoms are never used for rods which are more than about half an inch in diameter.