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15 1 4 Calculation example 2 for suction head (US)
Assumptions
Atmospheric pressure:
Suction pipe diameter:
Suction pipe length:
Fittings:
Valves:
Max. flow rate:
Calculation factor:
Safety margin:
Calculation
Step 1: Reading the NPSH graph
The NPSH curves for the corresponding pump type can be found in COMPASS, cf. "Figure
32: Reading NPSH graph, example 2" below. For a max. flow rate of 230 US GPM the NPSH
value is 9.5 ft.
Step 2: Determination of the friction losses
H
= H
/ 100 . (l
+ l
+ l
)
f
f,pipe
pipe
elbow
valve
The friction losses of the fitting and the valve can be read off from "Table 12: Friction loss
for valves and fittings – equivalent length of straight pipe" on page 31, as equivalent
length of straight pipe. For a pipe diameter of 4"the following applies:
ƒ l
= 7 ft
elbow
ƒ l
= 26 ft
valve
H
can be read from "Table 10: Friction loss in Schedule 40 steel pipe with Standard
f,pipe
Inside Diameter (SIDR)" on page 30. Since the max. flow rate is Q = 230 US GPM, H
must be interpolated with formula A.3
From the table, the following value can be read:
Q
= 200 US GPM H
= 2.27 ft
0
f0
H
(Q) = 3.06 ft
f,pipe
H
= 3.06 ft / 100 . (30 + 7 + 26) ft
f
H
= 1.93 m head
f
BERNT LORENTZ GmbH & Co. KG Kroegerskoppel 7, 24558 Henstedt-Ulzburg, Germany, Tel. +49 (0) 4193 7548 - 0, Fax - 29, www.lorentz.de
All specifi cations and information are given with good intent, errors are possible and products may be subject to change without notice. Pictures may
differ from actual products depending on local market requirements and regulations.
p
= 1.0 bar
0
4"
30 ft
1x long radius 90° pipe
1x check valve (swing)
Q = 230 US GPM
a = 33.5 ft (constant for all applications)
H
= 2 ft (minimum margin for all applications)
s
Q
= 300 US GPM H
= 4.91 ft
1
f1
Step 3: Determination of the vapor pressure
The value for Hv can be read from "Table 11: Vapour pressure" on page 30. At a temper-
ature of 104 °F the allowed suction head is reduced by 2.48 ft.
ƒ H
: 2.48 ft head
v
Step 4: Determination of the suction head
H = p
. a – NPSH – H
– H
0
f
H = 1.0 ∙ 33.5 ft – 9.5 ft – 1.93 ft – 2.48 ft – 2 ft
H = 17.59 ft head
Result
The result means that the pump can operate at a maximum suction lift of
H = 17.59 m head at 1 bar atmosphere pressure.
f,pipe
A.3
Figure 32: Reading NPSH graph, example 2
NPSH [ft]
12
3
9,5
9
6
3
0
0
25
50
33
– H
v
s
75
100
125
150
175
Sun. Water.
2
1
200
225
250
230
[US GPM]
Life.
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