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8
It may not, perhaps, be out of place in this Report
to give a brief description of the Lamp Meter in use.
It is a well-known fact to Gas Engineers and Gas
Manufacturers, that ordinary Consumers' Meters of
small capacity are very unreliable in their registration
when applied to Street Lamps, and should not on any
account be used for such purposes, hence the necessity
of having a Meter specially constructed, in order that
the friction may be reduced to a minimum. In the
Meter used scarcely half-a-tenth pressure is absorbed
by friction. It must not be expected from this that
any Meter will supply Gas for ordinary lighting purposes
at this low pressure ; but supposing the pressure
on the inlet-pipe to equal a column of water one inch
in height, the pressure at which the Gas would be
indicated on the outlet pipe, after passing the measuring
drum, would be nine-and-a-half-tenths, showing that
only half a tenth has been absorbed by friction in
working the Meter. This result is arrived at by the
increased diameter of the measuring wheel, which is
equal to a five-light Meter, and diminished in depth of
rim to nearly equal the capacity of a three-light
ordinary Meter, and the quantity passed per revolution
being .125 of a cubic foot, or 12 cubic feet per hour.
This extra diameter assists in distributing the pressure
further away from the central axis, thereby increasing
the leverage of the measuring drum, and of course
greatly reducing the friction. This class of Meter
cannot by any chance be overtaxed, or even worked
up to its maximum power, having only one light of
five cubic feet per hour to supply, and that controlled
by a governor at the burner.