FIG. 42A
FIG. 42B
Packing Glands
Where the shaft passes through the casing at either end it issues from a chamber in which there exists a vacuum. It is necessary to pack the shaft at these points, therefore, against the atmospheric pressure, and this is done by means of a water-gland packing W W (Fig. [34]). Upon the shaft in Fig. [35], just in front of the dummy pistons, will be seen a runner of this packing gland, which runner is shown upon a larger scale and from a different direction in Fig. [43]. To get into the casing the air would have to enter the guard at A (Fig. [44]), pass over the projecting rings B, the function of which is to throw off any water which may be creeping along the shaft by centrifugal force into the surrounding space C, whence it escapes by the drip pipe D, hence over the five rings of the labyrinth packing E and thence over the top of the revolving blade wheel, it being apparent from Fig. [43] that there is no way for the air to pass by without going up over the top of the blades; but water is admitted to the centrally grooved space through the pipe shown, and is revolved with the wheel at such velocity that the pressure due to centrifugal force exceeds that of the atmosphere, so that it is impossible for the air to force the water aside and leak in over the tips of the blades, while the action of the runner in throwing the water out would relieve the pressure at the shafts and avoid the tendency of the water to leak outward through the labyrinth packing either into the vacuum or the atmosphere.
FIG. 43