New England Water-Works Association. It should be borne in mind
that there is no water-hammer on this line. In 8,700 joints, 198,000 lb.
of lead and 3,200 lb. of oakum were used, or 22.76 and 0.37 lb. per
joint.
Leadite was tested in competition with lead, but it leaked at 100 lb. and
failed under a sustained pressure of 300 lb. It is a friable material, and
cannot be caulked successfully. Its principal ingredient appears to be
sulphur. The failure was by slow creeping out of the joints. It is melted
and poured, but not caulked. It has attractive features for low pressures
and for lines not subject to movement or heavy jarring.
_Air-Cushions_.--To prevent water-hammer on the pumping main, all
pumps are provided with large air-chambers. In addition, and as the
special feature for absorbing the shock of pumping under high pressure
through a pipe 21 miles long, a large air-chamber in the form of a
closed steel cylinder, 5 ft. in diameter and 15 ft. long, is mounted on the
pumping main outside of the pump-house. This cylinder is set on its
side, in concrete collars, directly over the pipe beneath, to which it is
connected by a 12-in. tee, in which a 12-in. gate-valve is set. The
cylinder is provided with a glass gauge, cocks, etc. It was designed for
a working pressure of 300 lb., and, at each pumping plant, it has proved
to be entirely air-and water-tight. As indicated by sensitive gauges on
the pump main, just beyond these large air-chambers, the latter absorb
all the water-hammer which gets beyond the air-chamber on the pumps.
_Air-Pumps_.--Each pumping plant is provided with four automatic
air-charging devices, connecting to all air-chambers of the pumps and
to the air-chamber on the pumping main. They are of the Nordberg type,
and have proved very efficient. They are operated only a part of the
time; otherwise, they accumulate too much air in the chambers.
_Air-Valves_.--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.
Safety Valves.--To prevent rupture of the pipe or injury to the pumps, in
case the pumping mains should become obstructed, a 6-in. pop safety
valve is mounted on the main just beyond the large air-chamber already
described. These valves are set to release at the maximum working
pressure of the pumps when the regular quantity of water is being
pumped, and they are piped to the adjacent reservoir, so that there is no
loss from them.
_Check-Valves_.--Check-valves are placed in the pumping main to
prevent the backward flow of water. There is one near the pumps, and
one at the upper end and outside of the reservoir into which the main
discharges.
_Blow-Off Valves_.--These valves are located in all material valleys or
depressions.
_Stand-Pipes_.--Between the gate-valves, at certain points where the
maximum hydraulic grade is not more than 60 ft. above the surface of
the ground, open stand-pipes are erected. If the grade line is too high,
relief-valves are used, as stated. Also at two points, where a steep grade
ends near the ground surface and is followed by a flatter grade,
stand-pipes are erected.
These stand-pipes are of 6-in. iron pipe standing in a special casting in
the pipe line and enclosed in a concrete base. They are, of course, open
at the top, and vary in height from 15 to 60 ft., depending on the
elevation of the hydraulic
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