some other non-corrosive metal. The spraying cone must be
thoroughly clean in every channel, to insure a well-distributed stream
of water. Nor is it less important that careful attention be given to
the setting and operation of the relief valve, as will be seen later.
The obvious object of such a valve is to prevent the internal condenser
pressure ever being maintained much higher than the atmospheric
pressure. A number of carefully designed rubber flap valves, or one
large one, have been found to act successfully for this purpose,
although a balanced valve of more substantial construction would appear
to be more desirable.

Importance of Relief Valves

The question of relief valves in turbine installations is an important
one, and it seems desirable at this point to draw attention to another
necessary relief valve and its function, namely the turbine atmospheric
valve. As generally understood, this is placed between the turbine and
condenser, and, should the pressure in the latter, owing to any cause,
rise above that of the atmosphere, it opens automatically and allows the
exhaust steam to flow through it into the atmosphere, or into another
condenser.

A general diagrammatic arrangement of a steam turbine, condenser, and
exhaust piping is shown in Fig. 73. Connected to the exhaust pipe B,
near to the condenser, is the automatic atmospheric valve D, from which
leads the exhaust piping E to the atmosphere. The turbine relief valve
is shown at F, and the condenser relief valve at G. The main exhaust
valve between turbine and condenser is seen at H. We have here three
separate relief valves: one, F, to prevent excessive pressure in the
turbine: the second, D, an atmospheric valve opening a path to the air,
and, in addition to preventing excessive pressure accumulating, also
helping to keep the temperature of the condenser body and tubes low; the
third, the condenser relief valve G, which in itself ought to be capable
of exhausting all steam from the turbine, should occasion demand it.

[Illustration: FIG. 73]

Assuming a plant of this description to be operating favorably, the
conditions would of necessity be as follows: The valves F, D, and G, all
closed; the valve H open. Suppose that, owing to sudden loss of
circulating water, the vacuum fell to zero. The condenser would at once
fill with steam, a slight pressure would be set up, and whichever of the
three valves happened to be set to blow off at the lowest pre