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.