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Hydraulic calculation
Hydraulic calculation can facilitate the selection of pump head and appropriate pipe diameter. Therefore,
hydraulic calculation must be carried out for verification after main pipeline selection and then adjust pump
head and pipe diameter based on the actual hydraulic calculation results.
Please refer to professional literature and design codes for hydraulic calculation.
Demonstration is made below by the calculation of fractional head loss and local resistance loss.
■ Fractional head loss calculation
Unit pipeline resistance loss can be calculated by Hazen-Williams formula according to the "Code for Design
of Building Water Supply and Drainage" (GB50015-2003):
I=10.5C
-1.85
d
j
-4.87
Q
1.85
Formula (13)
I— head loss of the unit pipeline, mH
2
O/m;
Q— flow rate, m
3
/s;
d
j
— pipeline inner diameter, m;
C— Hazen-William coefficient (see the table below).
Flow rate Q can be determined in actual engineering design process. Pipe diameter d
j
will be determined
as per the method specified below. Identify value C based on pipe material and then work out resistance
loss I of unit pipeline by Hazen-William formula. Therefore, supposing that the length of pipeline at a certain
diameter is L, the fractional head loss of the section of pipeline will be P=IL. Work out fractional head loss of
various sections of pipeline by the foresaid method. The total fractional head loss P
y
should be the sum of
fractional head loss of various pipeline sections, that is P
y
=ΣP=ΣIL.
The pipe diameter is determined based on the following:
The water speed should be determined by the recommendations in the first table and design the water pipe
diameters accordingly, or you can determine the water pipe diameter based on water flow in the second
table.
Table 1: Recommended water speed (m/s)
m
w
: water flow m
3
/s
v: water speed m/s
Pipeline All kinds of plastic pipes and
lined (coated) plastic pipes
Steel pipe,
stainless steel pipe
Cast iron pipe lined
with cement, resin
Ordinary steel pipe,
cast iron pipe
C
140
130
130
100
v
m
d
w
14
.
3
4
=
Diameter (mm)
12
20
25
32
40
50
65
80
Closed water
system
0.4 - 0.5
0.5 - 0.6
0.6 - 0.7
0.7 - 0.9
0.8 - 1.0
0.9 - 1.2
1.1 - 1.4
1.2 - 1.6
Open water
system
0.3 - 0.4
0.4 - 0.5
0.5 - 0.6
0.6 - 0.8
0.7 - 0.9
0.9 - 1.0
0.9 - 1.2
1.1 - 1.4
Diameter (mm)
100
125
150
200
250
300
350
400
Closed water
system
1.3 - 1.8
1.5 - 2.0
1.6 - 2.2
1.8 - 2.5
1.8 - 2.6
1.9 - 2.9
1.6 - 2.5
1.8 - 2.6
Open water
system
1.2 - 1.6
1.4 - 1.8
1.5 - 2.0
1.6 - 2.3
1.7 - 2.4
1.7 - 2.4
1.6 - 2.1
1.8 - 2.3
