ed in Fig. 71, which shows a turbine
spindle projecting through the casing. The gland box is let into the
casing as shown. Brass rings A calked into the gland box encircle the
shaft on either side of the annular steam space S. As the clearance
between the turbine spindle and the rings A is in a measure instrumental
in determining the amount of steam required to maintain a required
pressure inside the chamber, it is obvious that this clearance should be
minimum. An unnecessarily large clearance means a proportionally large
increase in gland steam consumption and _vice versa_.

[Illustration: FIG. 71]

When the turbine glands are sealed with water, all water leakage which
takes place into the turbine, and ultimately to the condenser hot-well,
must be measured and subtracted from the hot-well contents at the end of
a test.

The foregoing remarks would not apply to those cases in which the gland
supply is drawn from and returned to the hot-well, or a pipe leading
from the hot-well. Then no correction would be necessary, as all water
used for gland purposes might be assumed as being taken from the
measuring tanks and returned again in time for same or next weighing or
measurement.

General Considerations

There are a few principal elementary points which it is necessary always
to keep in mind during the conduct of a test. Among these are the
effects of variation in vacuum, superheat, initial steam pressure, and,
as already indicated, in load. There exist many rules for determining
the corrections necessitated by this variation. For example, it is often
assumed that 9 degrees Fahrenheit, excess or otherwise, above or below
that specified, represents an increase or reduction in efficiency of
about 1 per cent. It is probable that the percentage increase or
decrease in steam consumption, in the case of superheat, can be more
reliably calculated than in other cases, as, for example, vacuum; but
the increase cannot be said to be due solely to the variation in
superheat. In other words, the individuality of the particular turbine
being tested always contributes something, however small this something
may be, to the results obtained.

These remarks are particularly applicable where vacuum is concerned.
Here again rules exist, one of these being that every additional inch of
vacuum increases the economy of the turbine by something slightly under
half a pound of steam per kilowatt-hour. But a moment's consideration
convinces