1.659 | 1.576 | 18 13 3 | 17 14 7 |
_____________________________________________________________________

The great thing to guard against is leakage. If the pipes were simply
buried in the ground, it would be almost impossible to trace leakage, or
even to know of its existence. The income of the company might be
wasting away, and the loss never suspected until the quarterly returns
from the meters were obtained from the inspectors. Only then would it be
discovered that there must be a great leak (or it might be several
leaks) somewhere. But how would it be possible to trace them among 20 or
30 miles of buried pipes? We cannot break up the public streets. The
very existence of the concern depends upon (1) the _daily_ checking of
the meter returns, and comparison with the output from the air
compressors, so as to ascertain the amount of leakage; (2) facility for
tracing the locality of a leak; and (3) easy access to the mains with
the minimum of disturbance to the streets. It will be readily
understood, from the drawings, how this is effected. First, the pipes
are laid in concrete troughs, near the surface of the road, with
removable concrete covers strong enough to stand any overhead traffic.
At intervals there are junctions for service connections, with street
boxes and covers serving as inspection chambers. These chambers are also
provided over the ball-valves, which serve as stop-valves in case of
necessity, and are so arranged that in case of a serious breach in the
portion of main between any two of them, the rush of air to the breach
will blow them up to the corresponding seats and block off the broken
portion of main. The air space around the pipe in the concrete trough
will convey for a long distance the whistling noise of a leak; and the
inspectors, by listening at the inspection openings, will thus be
enabled to rapidly trace their way almost to the exact spot where there
is an escape. They have then only to remove the top surface of road
metal and the concrete cover in order to expose the pipe and get at the
breach. Leaks would mostly be found at joints; and, by measuring from
the nearest street opening, the inspectors would know where to break
open the road to arrive at the probable locality of the leak. A very
slight leak can be heard a long way off by its peculiar whistling sound.

[Illustration: COMPRESSED AIR POWER]

The next point is to obtain a daily report of the condition of the mains