The valve of the governor,
therefore, automatically throttles the gas-way more or less according to
the difference in pressure before and after the apparatus, until at any
moment the gas-way is just sufficient in area to pass the quantity of gas
which any indefinite number of burners require at their fixed working
pressure; passing it always at that fixed working pressure irrespective
of the number of burners, and maintaining it constant irrespective of the
amount of pressure anterior to the governor, or of any variations in that
anterior pressure. In most patterns of service governor weights may be
added when it is desired to increase the pressure of the effluent gas. It
is necessary, in ordering a governor for an acetylene-supply, to state
the maximum number of cubic feet per hour it will be required to pass,
and approximately the pressure at which it will be required to deliver
the gas to the service-pipe. This will usually be between 3 and 5 inches
(instead of about 1 inch in the case of coal-gas), and if the anterior
pressure is likely to exceed 10 inches, this fact should be stated also.
The mercury-seal governors are usually the more trustworthy and durable,
but they are more costly than those with leather diaphragms.
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