--On the entire line there are 144 automatic air-valves
made by the United States Metal Manufacturing Company, of Berwick, Pa.
They are working satisfactorily.
_Gate-Valves_.--In addition to the customary gate-and check-valves at
the reservoirs and pumping stations, gate-valves are located at
necessary points and elevations in the line to control the flow of water
and keep the pipe full, even to the extent of closing all such valves
tight and holding the line full without flow. This is for the purpose of
delivering through a full pipe any desired quantity of water less than
that required to keep the open pipe full. This, of course, is on account
of the wood pipe. As the differences of elevations are very great on the
gravity sections of the line, and as any one valve might inadvertently
become closed tight when other valves above would be open, the bursting
of the pipe under such conditions is prevented either by a pressure
relief valve attached to and immediately above the gate-valve, or by an
open stand-pipe erected on some suitable elevation between the valves.
This is more clearly shown on the profile, Plate V, of the ground line
and the hydraulic grades of the pipe line. An inspection of this profile
will show that these controlling valves are located so that, when
closed, the pressure against them does not rise above the maximum
pressure on the section above, due to the hydraulic grade of the line
when carrying its full capacity.
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