It must therefore both
cheek the pressure anterior to it whenever that is above the determined
limit to which it is set, and deliver to the efferent service-pipe
acetylene at a constant pressure whether all or any number of the burners
down to one only are in use. Moreover, when the pressure anterior to the
governor falls to or below the determined limit, the governor should
offer no resistance--entailing a loss of pressure to the passage of the
acetylene. These conditions, which a perfect governor should fulfil, are
not absolutely met by any simple apparatus at present in use, but so far
as practical utility is concerned service governors which are readily
obtainable are sufficiently good. They are broadly of two types, viz.,
those having a bell floating in a mercury seal, and those having a
diaphragm of gas-tight leather or similar material, either the bell or
the diaphragm being raised by the pressure of the gas. The action is
essentially the same in both cases: the bell or the diaphragm is so
weighted that when the pressure of the gas exceeds the predetermined
limit the diaphragm or bell is lifted, and, through an attached rod and
valve, brings about a partial closure of the orifice by which the gas
flows into the bell or the diaphragm chamber.
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