_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_.
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