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The minimum inlet pressure “H” in metres
head required to avoid cavitation in the
pumps can be calculated as follows:
H = pb x 10,2 - NPSH - Hf - Hv - Hs
pb = Barometric pressure in bar.
(Barometric pressure can be set to
1 bar.)
In closed systems, pb indicates the
system pressure in bar.
NPSH = Net Positive Suction Head in metres
head (to be read from the NPSH curves
in the installation and operating instruc-
tions for the pumps).
Hf = Friction loss in suction manifold in
metres head at the highest flow the
individual pump will be delivering.
Note:
If a non-return valve is installed
on the suction side of the pump, the
friction loss in the valve must be added.
See the manufacturer’s data
Hv = Vapour pressure in metres head.
(
Appendix B
)
tm = liquid temperature.
Hs = Safety margin = minimum 0.5 metres
head
If the calculated “H” is positive, the individual
pump can operate at a suction lift of maxi-
mum “H” metres head.
If the calculated “H” is negative, a minimum
suction head of “H” metres is required during
operation.
4.6 Minimum inlet pressure
ComBo systems with HP-E pumps require a positive inlet pressure during startup
and operation.
96202601_00
H
H
f
p
b
H
v
NPSH
Biral AG
Massstab
Zeichnungsnummer
I
II
Datum
Änd.Index
Visum
Ersatz f�r:
Änd.Index
Freigabe
gepr�ft
gezeichnet
PDM_Nr
Ersetzt durch:
®
CH-3110 M�nsingen
96202601
00
ComBo
Parameter Mindestzulaufdruck
Berechnung
%
13.04.2017 ts
13.04.2017 ts
13.04.2017 ts
TD-0036213
Example
pb =1 bar.
Pump type: HPE 18.
Flow rate: 15 m³/h.
NPSH (See catalog HPE): 1.4 m.
Hf = 3.0 m.
Liquid temperature: +60 °C.
Hv (Read from Appendix B): 2.1 m.
H = pb x 10.2 - NPSH - Hf - Hv - Hs [m].
H = 1 x 10.2 - 1.4 - 3.0 - 2.1 - 0.5 = 3.2 m.
This means that each pump can operate at a
suction lift of maximum 3.2 metres head.
Pressure calculated in bar:
3.2 x 0.0981 = 0.314 bar.
Pressure calculated in kPa:
3.2 x 9.81 = 31.4 kPa.
