ulated by a small motor wired to the switchboard. This spring should
be used only to correct slight changes in speed. Any marked change
should be corrected by the use of the large hexagonal nut in the upper
plate of the governor frame. This nut is screwed down to increase the
speed, and upward to decrease it.

[Illustration: FIG. 19]

The Stage Valves

Fig. 20 represents one of the several designs of stage valve, sometimes
called the overload valve, the office of which is to prevent too high
pressure in the first stage in case of a sudden overload, and to
transfer a part of the steam to a special set of expanding nozzles over
the second-stage wheel. This valve is balanced by a spring of adjustable
tension, and is, or can be, set to open and close within a very small
predetermined range of first-stage pressure. The valve is _intended_ to
open and close instantly, and to supply or cut off steam from the second
stage, without affecting the speed regulation or economy of operation.
If any leaking occurs past the valve it is taken care of by a drip-pipe
to the third stage.

[Illustration: FIG. 20]

The steam which passes through the automatic stage valves and is
admitted to the extra set of nozzles above the second-stage wheel acts
upon this wheel just the same as the steam which passes through the
regular second-stage nozzles; i.e., all the steam which goes through the
machine tends to hasten its speed, or, more accurately, does work and
_maintains_ the speed of the machine.

II. SETTING THE VALVES OF THE CURTIS TURBINE[2]

[2] Contributed to _Power_ by F. L. Johnson.

Under some conditions of service the stage valve in the Curtis turbine
will not do what it is designed to do. It is usually attached to the
machine in such manner that it will operate with, or a little behind, in
the matter of time, the sixth valve. The machine is intended to carry
full load with only the first bank of five valves in operation, with
proper steam pressure and vacuum. If the steam pressure is under 150
pounds, or the vacuum is less than 28 inches, the sixth valve may
operate at or near full load, and also open the stage valve and allow
steam to pass to the second-stage nozzles at a much higher rate of speed
than the steam which has already done some work in the first-stage
wheel. The tendency is to accelerate unduly the speed of the machine.
This is corrected by the governor, but the correction is usually carried
too far and