Therefore _p_ becomes = (35.333 x 389.1) / 48^2 = 5.97 inches,
instead of 6.07 inches.]
The value of _p_ for any position of the bell can thus be arrived
at, and if the difference between its values for the highest and for the
lowest positions of the bell exceeds 0.25 inch, [Footnote: This figure is
given as an example merely. The maximum variation in pressure must be
less than one capable of sensibly affecting the silence, steadiness, and
economy of the burners and stoves, &c., connected with the installation.]
a governor should be inserted in the main leading from the holder to the
burners, or one of the more or less complicated devices for equalising
the pressure thrown by a holder as it rises and falls should be added to
the holder. Several such devices were at one time used in connexion with
coal-gas holders, and it is unnecessary to describe them in this work,
especially as the governor is practically the better means of securing
uniform pressure at the burners.
It is frequently necessary to add weight to the bell of a small gasholder
in order to obtain a sufficiently high pressure for the distribution of
acetylene. It is best, having regard to the steadiness of the bell, that
any necessary weighting of it should be done near its bottom rim, which
moreover is usually stiffened by riveting to it a flange or curb of
heavier gauge metal.
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