21. SAMPLE
PROBLEM
-
ALLOWABLE
feet.
In
the
same
HEADLOSS
manner, the head loss is determined
a. Requirement.
Determine
the
for the 2-, 3-, and 6-inch diameter
allowable headloss Hf in the lines Al
pipes.
and A2 to provide at least 20 psi at
(1) Main AB.
Flow
=
100
gpm,
the latrine service connection and at
length = 1,400 feet.
least 30 psi at the laundry service
connection.
b. Solution.
In paragraph 16b the
allowable
headloss
was
given
as
Allowable Hf = E1Tk - (E1Sc + Hreq)
where the required head is equal to
the required pressure in psi times
2.31,
for
water.
The
allowable
headloss to each building is then
calculated as follows:
Hf Al = 200-[140' + (2.31 x 20 psi)] =
13.8'
Hf A2= 200[110'+ (2.31 x 30 psi)] =
20.7'
The allowable headloss is determined
for the service connection only, and
not points on the main.
22. SAMPLE PROBLEM
-
PIPE
SIZE
AND
The 2- and 3-inch pipes can be
ACTUAL HEADLOSS
eliminated at this point, as the
headlosses
produced
at
peak
flow
a. Requirement.
Select the pipe
exceed the maximum allowable from
sizes
and
determine
the
actual
point A to any point in the system.
headloss for the system.
Assume that
The 4-inch pipe can be eliminated as
C = 100, and that pipe is available in
the headloss from A to B is greater
2-, 3-, 4-, 6-, 8-, 10-, and 12-inch
than the maximum allowed from A to
diameter sizes.
building one.
b. Solution.
First
the
(2) Branch
B1.
The
actual
section of main from A to B will be
headloss to point B is now known for
considered.
The flow is 100 gpm; the
the size of pipe under consideration.
length 1,400 feet. From paragraph 17,
The pipe size for the branch line B1
the pipe size for the mains must be
can now be found. The total allowable
assumed.
Two, three, four, and six-
headloss from point A to building 1 was
inch pipe will be tried.
On figure
computed as 13.8 feet.
The actual
14, 100 gpm in the left column is
headloss from A to B was found to be
connected to 4 inches in the second
2.4 feet if 6-inch pipe is used. This
column.
The line is extended to
leaves 13.8 - 2.4 = 11.4 feet as the
intersect the third column as shown on
maximum that can be lost from point B
the figure.
From the intersection of
to building No. 1 if 6-inch pipe is
this
line
and
column
three,
the
used on the main AB. The length of the
headloss per 1,000 feet of pipe is
branch B1 is 400 feet. If 11.4 feet is
read as 12.5 feet.
Since the length
the largest allowable loss for 400
of
this
section
is
1,400
feet,
the
actual
headless
HfAB
is
3-22
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