Such breakage would be
followed by an escape of gas, and might lead to an accident. Fixed
pressure gauges, however, connected with every item of a plant are
extremely useful, and should be employed in all large installations, as
they afford great aid in observing and controlling the working, and in
locating the exact position of any block. All danger attending their use
can be obviated by having a stopcock between the gauge inlet and the
portion of the plant to which it is attached; the said stopcock being
kept closed except when it is momentarily opened to allow of a reading
being taken. As an additional precaution against its being left open, the
stopcock may be provided with a weight or spring which automatically
closes the gas-way directly the observer's hand is removed from the tap.
In the best practice all the gauges will be collected together on a board
fastened in some convenient spot on the wall of the generator-house, each
gauge being connected with its respective item of the plant by means of a
permanent metallic tube. The gauges must be filled with pure water, or
with a liquid which does not differ appreciably in specific gravity from
pure water, or the readings will be incorrect.
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