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.

[Illustration: FIG. 43]

[Illustration: FIG. 44]

The water should come to the glands under a head of about 10 feet, or a
pressure of about 5 pounds, and be connected in such a way that this
pressure may be uninterruptedly maintained. Its temperature must be
lower than the temperature due to the vacuum within the turbine, or it
will evaporate readily and find its way into the turbine in the form of
steam.

[Illustration: FIG. 45]

In any case a small amount of the steaming water will pass by the gland
collars into the turbine, so that if the condensed steam is to be
returned to the boilers the water used in the glands must be of such
character that it may be safely used for feed water. But whether the
water so used is to be returned to the boilers or not it should never
contain an excessive amount of lime or solid matter, as a certain amount
of evaporation is continually going on in the glands which will result
in the deposit of scale and require frequent taking apart for cleaning.

[Illus