and the third column the headloss per
storage to a point on the main where a
1,000 feet of pipe.
Knowing any two
branch is connected, is subtracted
of these, the third can be found by
from the allowable headloss to the
drawing a straight line through the
service connection at the end of the
two knowns.
As an example, assume
branch.
This will give the allowable
100gpm is flowing through a 1,000 foot
headloss
in
the
branch.
Then,
long pipe of 4-inch diameter.
Draw a
entering
the
nomograph
with
this
line passing through 100 gpm on the
headloss and the peak demand (flow) at
left column and 4 inches on the second
the service connection, the diameter
column.
Extending
the
line,
a
of pipe required can be obtained.
As
headloss of about 12-1/4 feet per
stated before, the nomograph gives
1,000 feet of pipe is obtained.
This
headloss per 1,000 feet of pipe, so
compares
very
well
with
values
conversions between the actual length
obtained by calculation.
of pipe and these values must be made.
If the pipe size obtained is one which
c. Headloss by use of figure 15.
is not available, use the next larger
Figure 15 gives the headloss per 1,000
size
which
is
available.
Then,
feet of pipe for any C from 70 to 160.
entering the nomograph with the flow
The left column is the coefficient of
rate and the selected pipe size, find
the
second
column
is
the actual headloss per 1,000 feet.
headloss per 1,000 feet of pipe, the
Convert this loss to the loss for the
third column is a pivot line, the
length of the branch. The headloss in
fourth column gives the pipe diameter,
the branch, plus the headloss in mains
and the right column gives the flow
to the point where the branch connects
rate.
The chart is used by drawing
to the main, will give the cumulative
two straight lines intersecting at the
headloss from storage to the service
pivot
line.
One
of
the
lines
connection.
This cumulative headloss
intersects the two columns to the left
must
not
exceed
the
allowable
of the pivot line, while the other
headloss.
intersects the two columns to the
18. SYSTEM DESIGN PROBLEM
right. The same example will be used.
100 gpm flows in a 1,000 foot long
pipe
of
4
inch
diameter.
The
To illustrate the application of the
coefficient of friction is 100.
The
design steps explained above, a sample
values of the two right columns are
water distribution system will be
known, so a straight line is drawn
designed for the following situation:
through 100 gpm and 4-inch diameter
A QM depot in a theater of operations
pipe.
This line is extended to
must have a water distribution system.
intersect the pivot line.
The second
Preliminary
studies
indicate
the
line must pass through this point, so
following:
the second line is drawn through the
intersection point on the pivot line
a. A troop strength of 50 officers
and through C = 100 on the left
and 700 EM.
column.
The headloss per 1,000 feet
of
pipe
can
be
read
at
the
b. Average
water
demand:
25
intersection of the second line with
gpd/man.
the headloss column.
A value of 12-
1/4 is obtained. This is shown by the
c. Laundry
water
requirements:
solid line on the figure.
A second
47,000 gpd.
example of the use of this nomograph
is given with the figure.
The
d. Sketch of system layout is shown
headloss in the mains can be found by
in figure 16.
use of any one of the above methods.
After having determined the actual
Numbers underlined are lengths of lines,
headlosses in the various sections of
numbers in parentheses ( ) are service
the mains, the actual headloss, from
3-20
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