3. The first of these (D) depends upon the movements of a
flexible diaphragm. A vessel (_a_) of any convenient size and shape
is divided into two portions by a thin sheet of metal, leather,
caoutchouc, or the like. At its centre the diaphragm is attached by some
air-tight joint to the rod _c_, which, held in position by suitable
guides, is free to move longitudinally in sympathy with the diaphragm,
and is connected at its lower extremity with a water-supply cock or a
carbide-feed gear. The tube _e_ opens at its base into the gas space
of the generator, so that the pressure below the diaphragm in _a_ is
the same as that elsewhere in the apparatus, while the pressure in
_a_ above the diaphragm is that of the atmosphere. Being flexible
and but slightly stretched, the diaphragm is normally depressed by the
weight of _c_ until it occupies the position _b_; but if the
pressure in the generator (_i.e._, in _e_) rises, it lifts the
diaphragm to somewhat about the position _b'_--the extent of
movement being, as usual, exaggerated in the sketch. The movement of the
diaphragm is accompanied by a movement of the rod _c_, which can be
employed in any desirable way.
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