assure the designer there will be no
adequate pressure will be available
point
along
the
line
where
the
even when a facility is drawing its
hydraulic gradient will fall below the
maximum
flow
(peak
demand).
At
required head at the outlet.
In the
military
installations
there
are
theater of operations, construction
essentially three times each day when
lines are normally located adjacent to
the peak demand will be approached.
roadways with a minimum number of
These times are in the morning when
crossings so that repair of the lines
the troops arise and breakfast is
will not affect traffic.
prepared, at midday when troops have
returned to the barracks for the noon
14. CHECK FOR EXCESS PRESSURE
meal, and in the late afternoon, at
the end of the duty day.
Unless the
For
standard
pipe,
the
maximum
population exceeds 1,000 men, the flow
pressure allowed anywhere in the line
rates in the mains and branches are
is 100 psi.
A check must be made at
found by summing the peak demands of
low points in a water line to insure
the facilities serviced by the line
that the pressure does not exceed 100
under
consideration.
If
the
psi.
If the pressure does exceed 100
population exceeds 1,000 men and there
psi, stronger pipe must be used or a
are large users, this simple addition
different layout determined.
The
of peak demands may be too high since
pressure at any point in the system
the peak demands may not occur at the
can
be
found
by
the
following
same time. In such a case, savings in
construction requirements can be made
by determining when the peaks occur
Pressure = 0.433 (E1Tk - El of point).
and using an adjusted peak demand
E1Tk is the elevation of the storage
based on engineering judgment and
tank.
experience.
El of point is the elevation of the
b. The peak demand of a facility
point in question.
depends on the number of outlets and
showers (fig 13).
(Any water fixture
For the pressure to be greater than
other than a shower is considered an
100 psi, the difference in elevation
outlet.)
If there are no showers in
must be as follows:
the facility, only the left column in
figure 13 need be used.
The peak
100 = 0.433 (E1Tk - El of point).
demand, in this case, is found on the
right side of the column opposite the
number of outlets found on the left
side.
If there are both showers and
Therefore, any pace where the line is
outlets, the peak demand is found by
more than 231 feet below the tank, the
connecting the number of outlets on
pressure, discounting friction losses,
the left column and the number of
will exceed 100 psi.
This type of
showers on the right column with a
static pressure check must be made for
straight line.
The peak demand is
every system to insure that the static
read
at
the
intersection
of
the
pressure in the line does not exceed
straight line and the center column.
the safe working pressure of the pipe.
16.
ALLOWABLE HEADLOSS
15.
PEAK DEMAND
a. Definition.
As
the
name
a. The source size and storage size
implies, allowable headloss is the
were
computed
using
the
average
maximum amount of head which may be
demand.
The
design
of
the
lost to friction between the storage
distribution system, however, is based
tank
and
the
facility
under
on the peak demand to insure that
consideration.
Thus, pipe sizes must
3-15
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