TABLE OF CONTENTS Pages Symposium 1 - the National Sea ...

Recirculation systems generally utilize pumps for moving water from the tank through
filters or from a sump through a filtering system. Four items are needed to correctly size a
pump:
(1) Desired flow rate (gpm or lpm)
(2) Friction loss from the piping and fittings (suction & discharge side)
(3) Vertical distance in which the water is to be pumped
(4) Pressure required by filters (1 psi = 2.31 head feet)
Creswell (1993) and Lawson (1997) gathered information on friction losses for selected
valves and fittings as “equivalent length of pipe”. Using this information, the total length
of all fittings is added to the length of straight pipe needed to give a total length of pipe
which is then used in the Hazen-Williams Formula. Major pipe sizes and their
corresponding friction losses are shown in Table 2. Lawson (1997) recommends using a
C-value of 100 for permanent installations of PVC piping due to future biofouling; new
PVC pipe has a C-value of 150. This calculation along with vertical lift and pressures
required by any filters will give the total dynamic head (ft or m). This information along
with the desired flow rate and a manufacturers pump graph will present the correct size
pump for the system.
Table 2.0
Losses are given in head feet per 100’ pipe using the Hazen-Williams formula. A C-value
of 130 is used as the coefficient using Schd. 40 PVC pipe. Velocities (v) are given in
ft/sec.
0.75 1
Pipe Size (in)
1.5 2 3
Loss v Loss v Loss v Loss v Loss v
GPM
5 10.17 3.63 9.05 2.04
10 36.73 7.26 32.67 4.09 1.26 1.82 0.31 1.02
20 132.58 14.52 69.21 8.17 4.53 3.63 1.12 2.04
30 117.9 12.26 9.61 5.45 2.37 3.06 0.33 1.36
40 178.24 16.34 16.37 7.26 4.03 4.09 0.56 1.82
50 24.75 9.08 6.10 5.11 0.84 2.27
60 34.68 10.89 8.54 6.13 1.19 2.72
70 10.99 7.15 1.58 3.18
80 13.43 8.17 2.02 3.63
90 15.89 9.19 2.51 4.09
100 18.37 10.21 3.05 4.54
110 3.64 4.99
120 4.28 5.45
130 4.97 5.90
140 5.70 6.35
150 6.47 6.81
Note: Generally 5 ft/sec is considered to be safe. Higher velocities may be used in cases where the
operating characteristics are known and that sudden changes in flow velocity can be controlled.
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