o 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