[Illustration: PLATE XIX.--DIAGRAM OF THE MAIN WATER PIPES OF MONTERREY.]
The distribution system was begun in September, 1906, but the general
lay-out of the mains was modified in July, 1907, in view of the division
of the system into two services, for high and low pressure. Plate XIX
shows in skeleton form the lines of the cast-iron mains. These are laid
at the present time along routes containing houses (excluding wooden
shacks) which can be served immediately. The distribution system is
arranged to serve as follows:
Estanzuela supply 4,150 houses.
San Geronimo supply 8,600 "
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Total 12,750 houses.
This represents, at the present time, a division of the city of 32-1/2%
for the Estanzuela, and 67-1/2% for the San Geronimo supply. Of the area
of the supply district north of Santa Catarina River, 57% will be
supplied from San Geronimo and 43% from Estanzuela. The real development
of the city, however, is northward in the area of the low-pressure
supply.
The static pressure over the city in the two sections varies as follows:
Estanzuela supply 85 to 50 lb.
San Geronimo supply 55 to 29 lb.
The main supply pipe from the South Reservoir is 61 cm. (24 in.) in
internal diameter, and this size allows ample provision for future
extensions. The supply pipe from the Obispado Reservoir is 76 cm. (30
in.) in internal diameter. On this main, in Calle de Cinco de Mayo, at a
distance of 320 m. from the reservoir, has been placed a 76-cm. (30-in.)
Venturi meter, the recording apparatus being in the house on the side of
the road. Both these supply pipes are carried well into the city, and
from them the distribution mains are laid; these are 45.7 and 30 cm. (18
and 12 in.) in internal diameter, with intermediate sections of 15 and
10 cm. (6 in. and 4 in.). Along Calle de Cinco de Mayo, where the
division between the two services takes place, two lines are laid, a
30-cm. for high pressure and a 38-cm. (15-in.) for the low pressure. A
duplicate pipe, 30 cm. (12 in.) in diameter, is also laid in Calle de
Dr. Coss. On Calle de Alvarez the low-pressure pipe is 61 cm. (24 in.),
and the high-pressure, 45.7 cm. (18 in.) in diameter. Provision is also
made for extending the range of the two services to other districts.
Practically every block is provided with gate-valves to cut off the
supply in any direction. On the 76-cm. main, 61-cm. (24-in.) valves are
used, and are connected by tapers to the pipe. On the 61-cm. mains,
45.7-cm. (18-in.) valves are used. The actual frictional loss by
reducing the valve being small, this method permitted the use of valves
of a more convenient size. On all the larger valves there are 15-cm.
by-passes fitted with independent gate-valves.
[Illustration: FIG. 15.--CONNECTION BETWEEN HIGH-AND LOW-PRESSURE AREAS
AND THE INTERSECTION OF CINCO DE MAYO AND ALVAREZ STREETS.]
Scour-out pipes, 10 cm. (4 in.) and 15 cm. (6 in.) in diameter, are
placed in various parts of the system, draining to the sewers.
Air-valves, both double and single, are also placed at high points in
different parts of the system.
_Reducing Valves._--At four points in the system the mains are arranged
so that the supply can be interchangeable. Fig. 15 shows the arrangement
of the mains at the junction of Cinco de Mayo and Alvarez Streets, and
is typical of the arrangement at the other points.
Each reducing valve is placed on a 30-cm. (12-in.) branch main between
the two services. These valves adjust themselves automatically to the
pressure required, after they have been properly regulated to the
different pressures on either side. To allow repairs to be easily made,
there are ordinary gate-valves at each end enclosed in the same pit. If
necessary, as in case of fire, any part of the system can be changed
into high pressure temporarily by closing the valves against the San
Geronimo supply.
Table 9 gives the length of the mains as laid, and the number of valves.