The gas
evolved follows the course shown by the arrows in the figure into the
gasholder, and raises the bell, thereby reversing the action of the
levers and allowing the valve to fall of its own weight and so cut off
the delivery of carbide. The outer stopper of the valve descends before
the inner plunger and so leaves the conical delivery mouth of the hopper
free from carbide. The inner plunger, which is capped at its lower end
with rubber, then falls and seats itself moisture-tight on the clear
delivery mouth of the hopper. The weight of the carbide in the hopper is
taken by its sides and a projecting flange of the valve casing, so that
the pressure of the carbide at the delivery point is slight and uniform.
The outside of the delivery mouth is finished by a drip collar with
double lip to prevent condensed moisture creeping upwards to the carbide
in the hopper. A float in the generating tank, by its descent when the
water falls below a certain level, automatically draws a cut off across
the delivery mouth of the carbide hopper and so prevents the delivery of
carbide either automatically or by hand until the water in the generating
tank has been restored to its proper level.
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