e._, a fall in pressure, as
a gas travels along a pipe; and, as will be shown in Chapter VII., it is
the fall in pressure in a pipe rather than the initial pressure at which
a gas enters a pipe that governs the volume of gas passing through that
pipe. The proper behaviour and economic working of a burner (acetylene or
other, luminous or incandescent) naturally depend upon the pressure in
the pipe to which the burner is immediately attached being exactly suited
to the design of that burner, and have nothing to do with the fall in
pressure occurring in the delivery pipes. It is therefore necessary to
keep entirely separate the ideas of proper burner pressure and of maximum
desirable fall in pressure within the service due to friction.] and
(d) to give at the points of combustion a pressure which is
required by the particular burners adopted. In all except village or
district installations, (_c_) may be virtually neglected. When the
holder has a rising bell, (_a_) represents only an inch or so of
water; but if a displacement holder is employed the pressure needed to
work it is entirely indeterminate, being governed by the size and shape
of the said holder.
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