e governing valve D; a
gage I must consequently be placed between the valve, preferably on the
valve itself, and the turbine. Returning to Fig. 74, the gages shown are
A, B, C, D, and E, connected to the first, second, third, fourth, and
fifth expansions; also F in the turbine and exhaust space, where there
are no blades, G in the exhaust pipe immediately before the main exhaust
valve E (see Fig. 73), and H connected to the condenser. On condensing
full load it is probable that A, B, and C will all register pressures
above the atmosphere, while gages D, E, F, and G will register pressures
below the atmosphere, being for this purpose vacuum gages. On the other
hand, with a varying load, and consequently varying initial pressures,
one or two of the gages may register pressure at one moment and vacuum
at another. It will therefore be necessary to place at these points
compound gages capable of registering both pressure and vacuum. With the
pressures in the various stages constantly varying, however, a gage is
not by any means the most reliable instrument for recording such
variations. The constant swinging of the finger not only renders
accurate reading at any particular moment both difficult and, to an
extent, unreliable, but, in addition, the accompanying sudden changes of
condition, both of temperature and pressure, occurring inside the gage
tube, in a comparatively short time permanently warp this part, and thus
altogether destroy the accuracy of the gage. It is well known that even
with the best steel-tube gages, registering comparatively steady
pressures, this warping of the tube inevitably takes place. The quicker
deterioration of such gage tubes, when the gage is registering quickly
changing pressures, can therefore readily be conceived, and for this
reason alone it is desirable to have all gages, whatever the conditions
under which they work, carefully tested and adjusted at short intervals.
If it is desired to obtain reliable registration of the several
pressures in the different expansions of a turbine running on a varying
load, it would therefore seem advisable to obtain these by some type of
external spring gage (an ordinary indicator has been found to serve well
for this purpose) which the sudden internal variations in pressure and
temperature cannot deleteriously affect.

In view of the great importance he must attach to his gage readings, the
tester would do well to test and calibrate and adjust where necess