ssure would
do so. Now it is desirable that the first valve to open under such
circumstances should be the atmospheric valve D. This being so, the
condenser would remain full of steam at atmospheric pressure until the
attendant had had time to close the main hand-or motor-operated exhaust
valve H, which he would naturally do before attempting to regain the
circulation of the condensing water. Again, assume the installation to
be running under the initial conditions, with the atmospheric valve D
and all remaining valves except H closed.

Suppose the vacuum again fell to zero from a similar cause, and,
further, suppose the atmospheric valve D failed to operate
automatically. The only valves now capable of passing the exhaust steam
are the turbine and condenser relief valves F and G. Inasmuch as the
pressures at exhaust in the turbine proper, on varying load, vary over a
considerably greater range than the small fairly constant absolute
pressures inside the condenser, it is obviously necessary to allow for
this factor in the respective setting of these two relief valves. In
other words, the obvious deduction is to set the turbine relief valve to
blow off at a higher pressure than the condenser relief valve, even
when considering the question with respect to condensing conditions
only. In this second hypothetical case, then, with a closed and disabled
atmospheric valve, the exhaust must take place through the condenser,
until the turbine can be shut down, or the circulating water regained
without the former course being found necessary.

There is one other remote case which may be assumed, namely, the
simultaneous refusal of both atmospheric and condenser relief valves to
open, upon the vacuum inside the condenser being entirely lost. The
exhaust would then be blown through the turbine relief valve F, until
the plant could be closed down.

Although the conditions just cited are highly improbable in actual
practice, it can at once be seen that to insure the safety of the
condenser, absolutely, the turbine relief valve must be set to open at a
comparatively low pressure, say 40 pounds by gage, or thereabouts. To
set it much lower than this would create a possibility of its leaking
when the turbine was making a non-condensing run, and when the pressure
at the turbine exhaust end is often above that of the atmosphere. From
every point of view, therefore, it is advisable to make a minute
examination of all relief valves in a